Pascal Casari

Laurent Gornet

Characterization of residual stresses in a composite curved sandwich beam

Keywords: Sandwich structure, B. Residual stress, C. Finite element analysis, D. Mechanical testing

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Introduction

The aim of this study is to investigate the thermomechanical response of a sandwich composite shell, which exhibits a double curvature. In this kind of heterogeneous structure, the skins and the core play very different roles. The skins are stiff and their coefficient of thermal expansion (noted CTE) is low. The foam core has stiffness 1000 times lower than the stiffness of the layers in the direction of the fibers and expands 10 times more. Residual stress control is required to ensure the geometrical stability of the structure, and for this reason it is important to measure the order of magnitude of these stresses. For single laminates, it has been shown in [START_REF] Bogetti | Process-induced stress and deformation in thick-section thermoset composite laminates[END_REF][START_REF] White | Process modeling of composite materials: residual stress development during cure. Part II. Experimental validation[END_REF][START_REF] Ridgard | Accuracy and distortion of composite parts and tools: causes and solutions[END_REF][START_REF] Radford | Measurement of manufacturing distortion in flat composite laminates[END_REF][START_REF] Johnston | A plane strain model for process induced deformation of laminated composite structures[END_REF][START_REF] Fernlund | Experimental and numerical study of the effect of cure cycle, tool surface, aspect ratio, and the lay-up on the dimensional stability of autoclave-processed composite parts[END_REF][START_REF] Gigliotti | Development of curvature during the cure of AS4/8552 [0/90] unsymmetric composite plates[END_REF] that the significant phenomena responsible for residual strain are chemical and thermal shrinkage, and frictional effects in combination with moulds whose constitutive materials have different coefficients of thermal expansion to the manufactured composites. In those published studies, modelling of residual stresses has progressed, but they concern mostly laminates. Only a few studies have been performed on sandwich structures, and essentially on flat panels [START_REF] Matsunaga | Assessment of a global higher-order deformation theory for laminated composite and sandwich plates[END_REF][START_REF] Matsunaga | Interlaminar stress analysis of laminated composite and sandwich circular arches subjected to thermal/mechanical loading[END_REF][START_REF] Matsunaga | A comparison between 2-D single-layer and 3-D layerwise theories for computing interlaminar stresses of laminated composite and sandwich plates subjected to thermal loadings[END_REF]. In the present work, a set of experiments has been performed going from the scale of the structure down to the scale of its constitutive parts. First, tests carried out on the sandwich structure provide an order of magnitude of residual stresses. Then curved beams, easier to test, are cut from the sandwich shell, and are subjected to the removal of edges and outer skin. Thus, materials or structures can be characterized in the range of thermal and mechanical loadings encountered in the structure's life. Once material properties have been identified (or collected from datasheets), a thermo-mechanical finite element model (noted FEMo) has been built and is used to simulate the heating of a beam simply supported at the ends.

Measurement of residual stresses and materials properties

Sandwich panel

The sandwich shell under consideration is part of a radar antenna (see Fig. 1), It has been designed mostly with process constraints, and no calculations were run before manufacture. It has a double curvature and is approximately 2 m wide, 0.9 m high and 50 mm thick. After manufacturing, this structure shows a slight twist, and a residual deflection, which tends to hollow out the panel. This effect can be attributed to the thermal shrinkage of both skins and core during polymerization and to the difference of coefficients of thermal expansion of skins and core when cooling down from 80 8C to room temperature. The cure cycle of the structure is 8 h at 80 8C. The initial state of the structure can be considered as the non-stressed state at curing temperature. From then on, residual stresses remain in the constituents. The main idea proposed in this study is to give an order of magnitude of residual stresses by cutting a piece from the sandwich panel (Fig. 2). Strains released from the cutting are measured by means of triaxial strain gages bonded on both faces. Under elastic hypotheses, the corresponding stresses are given in Fig. 3 (Table 1 for the description of the skin stacking sequence). The first remark is that strains remain low but significant. On both sides, the plies are predominantly in tension in the width direction of the panel. An opposite global shear deformation appears between the two skins, which leads to the confirmation of a global twist which has been observed on the shell. Regarding stresses in each ply, they are low and match the global equilibrium, so that the core is consequently in compression in the width direction. Shear in the plies is much lower than tensions or compressions in the fiber directions. This means that the stacking sequence seems convenient for storing energy in the principal directions of the plies and not in shear. In fact, the symmetry of the structure associated with the viscoelasticity of the matrix tends to reduce the residual stresses. In addition to this first step of characterization, a finite element model has been constructed with NISAe. It consists in modelling the panel with linear rectangular shell elements for the skins and three-dimensional elements for the core as detailed in Fig. 4. The inputs are both mechanical and thermal properties, measured on coupons and presented later. The predicted maximum deflection of the panel is 2.6 mm but the geometrical report on the shape of a manufactured panel gave a value of 0.6 mm. This measurement of deflection had been completed several days after curing. Numerical and experimental results were not comparable: a significant mismatch was appearing in the strains, stresses and deflection results. This led to the need of accurate modelling and characterization of each component of the sandwich material in order to explain this gap.

Sandwich beam

A second set of experiments has been conducted on a sandwich beam extracted from the structure. The aim was to find out which components of the sandwich are responsible for the residual stresses. The removal operations are illustrated in Fig. 5. The beam is 50 mm wide. The displacement field is then measured by means of a testing device, which simply supports the beam (Fig. 6) on both ends. The first step consists of cutting the beam from the panel. The residual stress field then becomes unidirectional. Through the second step, the effect of the edges on the shape of the beam is analyzed. This stems from a study conducted in [START_REF] Cheng | Reduction of the concentrated residual stress on the edges of a sandwich plate[END_REF] in which some sharp corners in the sandwich have been found to cause very high stress concentrations at the beam's tips. Here, the removal of the edges has no significant effect in terms of deflection of the beam. The last step is the removal of the outer skin in order to release residual stresses included in this component. Deflection variations (Fig. 7) are taken in a regular 300 mm-long part of the beam (Fig. 6). The graph in Fig. 7 shows that the most important effect is due to the skin removal: the beam tends to flatten out. This leads to the conclusion that internal stresses probably remain in tension and in compression in the skins and in shear in the foam core. A possible interpretation of the curvature is to calculate the corresponding bending moment that must be applied in order to return to the initial shape (before cutting). The result is presented in Table 2. In addition, it may be noted that the sandwich structure is not symmetrical through the thickness. The beam deflection due to heating will be compared to the Fig. 5. Removal operations on a sandwich beam in order to release residual stresses.

response of FEMo in the 'finite element modelling' section below.

Material properties

Thermal expansion and mechanical tests have been conducted on the constitutive parts of the sandwich in order to quantify the properties required for the FEMo analysis. The identification has been made on the two different plies used in the lamination of the sandwich shell. These are a twill woven carbon fabric and a stitched [G45] made of two unidirectional plies. The properties of the core have been taken from the manufacturer's datasheet. The estimated material properties required for modelling are listed in Table 3. The 08 direction of the panel and of the laminates is the x axis plotted in Fig. 5.

Skins

In order to characterize the constitutive plies of the skins, two specific plates (called twill and stitched) have been manufactured with the same process as that used for the sandwich shell. The twill plate is made of a twill balanced fabric and has a [0,G30] S stacking sequence. This ensures a mirror symmetry and produces a quasi-isotropic composite laminate. In the stitched plate, six layers have been stacked in the 08 direction. A mirror symmetry cannot be exactly used here, and the direction of maximum stiffness is 458. From each plate, seven coupons have been cut every 158 from 0 to 908 (Fig. 8).

From the stress-strain curves obtained, the elastic modulus, the Poisson's ratios and the coefficients of thermal expansion could be measured. Results confirm that the twill laminate can be considered as a quasiisotropic material. For the stitched laminate, these properties are plotted in Fig. 9 and show that the behaviour cannot be considered as quasi-isotropic. Moreover, classical laminate theory cannot match completely these results because, due to its constitution, the laminate should have the same properties in the directions (q), (Kq), and (p/2Kq). A compromise has been found in the choice of the properties of this layer: the evolution of elastic and thermal parameters versus angle is plotted in addition to experimental results. The discrepancy is probably due to movement of the stitched layers during lamination: dry layers are very deformable and the specific angle of 458 can vary rapidly by 5-108 under a stretching action. Nevertheless, elastic properties are well simulated. Only the evolution of the coefficient of thermal expansion is not satisfactory because the variations around the average vary from negative to positive values.

Core

The foam core is a very soft material compared to the skins. Its properties are recalled in Table 3 from the manufacturer's datasheet. A special feature of the core properties is the difference in stiffness from tension to compression. This particularity could not be taken into account in modelling, but it may have a significant effect on the stress and strain fields in the sandwich shell and beam. The core is considered here as a linear elastic and isotropic material, and its behaviour has to be included as three-dimensional in modelling with tensile Young's modulus. Indeed, because of the sandwich curvature, the thermal expansion of the core through the thickness leads to a variation of this curvature.

Modelling of the sandwich beam

Modelling is now focused on the behaviour of the beam extracted from the shell in order to simulate a heating experiment applied on the beam. In this test, the beam is simply supported at the ends and heated with a temperature-controlled airflow. The upper and lower displacements in the mid-section are recorded. Deflection and thickness variation of the beam can be deduced a f t e ra ni n c r e a s eo f6 08C, representing the heating of the structure from room to curing temperature.

Thermo-mechanical analysis

After heating, the core has forced the curved composite shell to expand through the thickness and the skins have also expanded; this leads to a new internal equilibrium and the existence of internal stresses. This effect can be taken into account in the finite element calculations if the core is modelled with three-dimensional elements. The skins are considered in a plane stress state with the same stacking sequence as for the panel (Table 1). The finite element code Cast3M capability for coupled thermo-mechanical heat transfer analysis is used in order to model heat conduction in the multi-layer composite sandwich structure and to determine the elastic strain and stress induced by temperature variations. Both steady-state and transient heat transfer finite element capabilities have been used for computations, but here only the first one is taken into consideration. Predictions are made with both composite shell and second order tetrahedral and full Lagrange heat conduction brick elements (Fig. 10). Classical thermal boundary conditions such as the surface heat flux or the properties of the surface convection must be specified. In order to model the experimental facilities, only surface convection boundary conditions are used.

Results

At first, deflection results have been calculated versus the CTE value of the stitched layers, varying from K1!10 K6 to 7!10 K6 8C K1 as mentioned in Fig. 9. Resulting deflection and thickness variation of the beam are plotted in Fig. 11 and compared to experimental values. The calculated deflection is sensitive to this parameter, and the value of CTE for the stitched layers which fits the experiment is close to 4.7!10 K6 8C K1 . This choice of a constant CTE must be done because its evolution shown in Fig. 9 cannot be reproduced in numerical simulations. Thickness variation from the test and the simulation are very close, which indicates that t h eC T Eo ft h ec o r ei ss a t i s f a c t o r y .R e s u l t si nt e r m so f stresses in the skins are calculated from the model with the above-mentioned CTE value and given in Table 4. A significant stress level (maximum of 28.1 MPa in a twill layer of the outer skin) is created by the internal equilibrium and shows that the highest stresses are located in the outer skin and due to the difference of CTE between the four constitutive layers.

Compared to the stress level measured on the panel from strain analysis (maximum of 7 MPa in one of the stitched plies), it seems that this increase of 60 8C generates more stresses than the ones remaining in the structure after manufacturing. These stress levels are not completely comparable, but this order of magnitude is a typical one that may create creep deformations and affect the geometrical stability of the structure.

Conclusion

The approach presented in this article is based on a procedure of characterization of residual stresses that can be applied to any sandwich structure for which destructive tests are possible. Data collected among displacements, curvatures or strains have been selected and consistently compared with calculations. These specific results have given some orders of magnitude of residual stresses, but have also underlined the need for accurate mechanical and thermal material properties. Indeed, some parameters like the evolution of the CTE of the stitched layers are not explained by classical laminate theory, and require more accurate investigations. This approach is not comprehensive yet, because only a few data and measurements are available for the core. Moreover, there is no up-to-date measurement technique for stress analysis and thermal characterization and only the thickness variation of the beam with temperature could be validated. Work on the thermomechanical and viscous properties of the core are probably the next aspects to study.

Fig. 1 .

 1 Fig. 1. Sandwich panel and mismatch between theoretical and manufactured shapes.

Fig. 2 .Fig. 3 .

 23 Fig. 2. Piece of sandwich cut out from the structure, and direction of the strain gages.

Fig. 4 .

 4 Fig. 4. FEMo of the panel and transverse displacement field.

Fig. 6 .

 6 Fig. 6. Test device for curvature evolution on sandwich beams.

Fig. 7 .

 7 Fig. 7. Deflection of the beam after part removal.

Fig. 8 .

 8 Fig. 8. Geometry and direction of the tensile coupons.

Fig. 10 .

 10 Fig. 10. FEMo of the sandwich beam.

Fig. 11 .

 11 Fig. 11. Deflection of the beam and thickness variation vs CTE of the stitched layer.

Table 1

 1 Properties of the sandwich panel

	Component	Thickness (mm)	Stacking sequence
	Outer skin	1.6	1 Twill fabric K308
			2 Stitched fabrics 08
			1 Twill fabric C308
	Inner skin	0.7	1 Twill fabric K308
			1 Twill fabric 08
			1 Twill fabric C308
	Core	50

Table 3

 3 Thickness 0.23 mm E x ZE y Z40 GPa, n xy Z0.1, G xy Z3 GPa 3 Stitched ply Carbon T300, 2 layers at [G45] 440 g/m 2 , Thickness 0.45 mm E x ZE y Z56 GPa, n xy Z0.04, G xy Z3.3 GPa

	Material properties
	Constitutive materials properties of the sandwich	Geometric	Mechanical	CTE!10 6 m/m
	Twill fabric	Carbon T300, [0;90]	220 g/m 2 , 3
	Resin	Aralditee LY5052-HY5052	Fiber volume fraction:
			40!V f !46
	Core	Klegecelle R55	55 kg/m 3	E

compression Z77 MPa, E tension Z51 MPa, GZ27 MPa, nZ0.32 35 Fig. 9. Mechanical and thermal behaviour of the stitched layers.

Table 4

 4 FEMo results of stress-state in the plies of the beam after 60 8C heating

		Thickness (mm)	Stiffness matrix		Stresses (MPa) (in the coordinate system of each ply)
						Ply	s xx	s yy	s xy
	Inner skin	0.7	0 B @	3:28 1:16 0 1:16 3:28 0 001 :06	1 C A !10 4	Twill [K30] Twill [0] Twill [30]	7.3 6.1 4.6	4.4 0.7 K2.9	0.1 K0.1 0.1
	Outer skin	1.6	0 B @	3:06 2:16 0 2:16 3:06 0 002 :20	1 C A !10 4	Twill [K30] Stitched [45] Stitched [45] Twill [K30]	26.2 K5.5 K6.4 23.1	28.1 K6.5 K8.6 19.6	K1.2 0.1 0.1 1.0


Hicham Ait Laasri
email: hicham.aitlaasri@univ-tours.fr

Eliane Bsaibess

Fabian Delorme

Guillaume F Nataf

Fabien Giovannelli
email: fabien.giovannelli@univ-tours.fr

Ultra-low lattice thermal conductivity in tungsten-based scheelite ceramics

Keywords: Tungsten-based scheelites, Defect scheelite-type, Low thermal conductivity, Solidstate synthesis

BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 polycrystalline ceramics were synthesized by conventional solid-state reaction route. The effect of cation-deficiency on the crystallographic structure, microstructure and thermal properties of these scheelite-type compounds were investigated. X-ray diffraction was used to identify the single-phase scheelite structure of the studied ceramics. Scanning Electron Microscopy technique has revealed a homogenous and dense microstructure with a few micro-cracks. The thermal conductivity of BaWO4 scheelite decreases from 1.3±0.2 to 1.0±0.1 W m -1 K -1 in the range 373 K -673 K. The cation-deficient scheelites Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics display an ultra-low thermal conductivity of 0.3±0.04 W m -1 K -1 and 0.2±0.03 W m -1 K -1 at 673 K, respectively. These materials exhibit among the lowest known values of thermal conductivity in crystalline oxides, in this temperature range. Therefore, they appear as very attractive for thermal barrier coating and thermoelectric applications.

Introduction

The discovery of materials with low thermal conductivity offers great opportunities for many applications [START_REF] Zheng | Advances in thermal conductivity for energy applications: A review[END_REF] such as thermal barrier coatings (TBCs) [START_REF] Clarke | Thermal-barrier coatings for more efficient gasturbine engines[END_REF][START_REF] Padture | Advanced structural ceramics in aerospace propulsion[END_REF][START_REF] Fergus | Zirconia and pyrochlore oxides for thermal barrier coatings in gas turbine engines[END_REF][START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF] and solid-state thermoelectric converters [START_REF] Poudel | High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys[END_REF][START_REF] Tan | Rationally Designing High-performance bulk thermoelectric materials[END_REF]. With the extensive demand for more efficient and powerful aero-engines, the development of advanced thermal barrier coatings has attracted impressive attention to find suitable thin oxide-ceramics (1µm -5µm), particularly useful for gas turbine blades to thermally insulate air-cooled metallic components from hot gases in the engine, enhancing their combustion efficiency, performance, and longevity [START_REF] Clarke | Thermal-barrier coatings for more efficient gasturbine engines[END_REF]. Nowadays, 7-8 wt. % yttria-stabilized zirconia (YSZ) is the main successful ceramic oxide used as thermal barrier coating due to its impact resistance, low thermal conductivity (∼1.5-3 W m -1 K -1 ) [START_REF] Fergus | Zirconia and pyrochlore oxides for thermal barrier coatings in gas turbine engines[END_REF], high thermal expansion, high melting point and excellent chemical stability [START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF].

Nevertheless, its structural phase transition at temperatures above 1473 K increases the risk of crack propagation [START_REF] Vagge Atul | Synthesis and processing of thermal barrier coatings with the use of YSZ, LTA and LTA/YSZ[END_REF][START_REF] Shen | Thermal shock life and failure behaviors of La2Zr2O7/YSZ, La2Ce2O7/YSZ and Gd2Zr2O7/YSZ DCL TBCs by EB-PVD[END_REF]. To improve the performances of TBCs, several scientific and technical approaches have been adopted to discover material with low thermal conductivity. Previous studies have reported that some inorganic materials, such as rare earth zirconates [START_REF] Cheng | Prolong the durability of La2Zr2O7/YSZ TBCs by decreasing the cracking driving force in ceramic coatings[END_REF], pyrochlore oxides [START_REF] Feng | Thermal expansion and conductivity of RE2Sn2O7 (RE = La, Nd, Sm, Gd, Er and Yb) pyrochlores[END_REF] or La2Mo2O9-based compounds [START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF][START_REF] Sabarthes | Reducing the thermal conductivity of La2Mo2O9 with a trivalent praseodymium substitution for its potential use as a thermal barrier coating[END_REF] exhibit a lower thermal conductivity than YSZ [START_REF] Fergus | Zirconia and pyrochlore oxides for thermal barrier coatings in gas turbine engines[END_REF]. Recently, low thermal conductivity has been reported in high entropy oxides [START_REF] Wright | Size disorder as a descriptor for predicting reduced thermal conductivity in medium-and high-entropy pyrochlore oxides[END_REF][START_REF] Song | Glass-like thermal conductivity in mass-disordered high-entropy (Y, Yb)2(Ti, Zr, Hf)2O7 for thermal barrier material[END_REF][START_REF] Vayer | New entropy-stabilized oxide with pyrochlore structure: Dy2(Ti0.2Zr0.2Hf0[END_REF] or guided by probe structure and machine learning [START_REF] Collins | Discovery of a low thermal conductivity oxide guided by probe structure prediction and machine learning-Angew[END_REF]. Besides, due to the development of global economy, the demand for energy is considerably increasing for industrial production and human life.

Thermoelectric materials, which can directly convert waste heat into electricity, are the subject of numerous studies [START_REF] Wu | Thermoelectric converter: Strategies from materials to device application[END_REF]. High thermoelectric performance can be achieved by increasing the power factor and reducing the thermal conductivity of materials [START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF][START_REF] Poudel | High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys[END_REF][START_REF] Qian | Phonon-engineered extreme thermal conductivity materials[END_REF][START_REF] Kanatzidis | Nanostructured thermoelectrics: the new paradigm[END_REF]. In this research field, many different routes have been explored to decrease the thermal conductivity of promising materials such as alloying, nano-structuring, composites, microcracking approaches or improving electrical properties of intrinsic low thermal conductivity materials [START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF][START_REF] Poudel | High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys[END_REF][START_REF] Qian | Phonon-engineered extreme thermal conductivity materials[END_REF][START_REF] Kanatzidis | Nanostructured thermoelectrics: the new paradigm[END_REF][START_REF] Giovannelli | Thermal conductivity and stability of Al-doped ZnO nanostructured ceramics[END_REF][START_REF] Chen | Thermopower and chemical stability of Na0.77CoO2/Ca3Co4O9 composites[END_REF][START_REF] Delorme | Thermoelectric properties of Ca3Co4O9-Co3O4 composites[END_REF][START_REF] Delorme | Nanostructuring of dense SnO2 ceramics by Spark Plasma Sintering[END_REF][START_REF] Chen | Thermoelectric properties of Fe2(Ti1-xNbx)O5 pseudobrookite ceramics with low thermal conductivity[END_REF][START_REF] Yin | A Review of Strategies for Developing Promising Thermoelectric Materials by Controlling Thermal Conduction[END_REF][START_REF] Zhao | Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals[END_REF]. Increasing crystal complexity is one of these approaches to obtain ultra-low lattice thermal conductivity in inorganic materials [START_REF] Sabarthes | Reducing the thermal conductivity of La2Mo2O9 with a trivalent praseodymium substitution for its potential use as a thermal barrier coating[END_REF][START_REF] Qian | Phonon-engineered extreme thermal conductivity materials[END_REF][START_REF] Li | Crystal structure induced ultralow lattice thermal conductivity in thermoelectric Ag9AlSe6[END_REF][START_REF] Cherniushok | Crystal structure and thermoelectric properties of novel quaternary Cu2MHf3S8 (M-Mn, Fe, Co, and Ni) thiospinels with low thermal conductivity[END_REF]. Previous studies focused on complex crystal structures and materials that have a large unit cell volume and a large molecular weight, due to the large population of diffuson-like modes [START_REF] Sabarthes | Reducing the thermal conductivity of La2Mo2O9 with a trivalent praseodymium substitution for its potential use as a thermal barrier coating[END_REF][START_REF] Qian | Phonon-engineered extreme thermal conductivity materials[END_REF][START_REF] Li | Crystal structure induced ultralow lattice thermal conductivity in thermoelectric Ag9AlSe6[END_REF][START_REF] Cherniushok | Crystal structure and thermoelectric properties of novel quaternary Cu2MHf3S8 (M-Mn, Fe, Co, and Ni) thiospinels with low thermal conductivity[END_REF]. Another promising approach to reduce the thermal conductivity is to introduce cation vacancies [START_REF] Popuri | Glass-like thermal conductivity in SrTiO3 thermoelectrics induced by A-site vacancies[END_REF][START_REF] Lu | High-Figure-of-Merit Thermoelectric La-Doped A-Site-Deficient SrTiO3 Ceramics[END_REF][START_REF] Kovalevsky | Effect of A-Site Cation Deficiency on the Thermoelectric Performance of Donor-Substituted Strontium Titanate[END_REF][START_REF] Delorme | Low intrinsic thermal conductivity of Spark Plasma Sintered dense KNbO3 and NaNbO3 perovskite ceramics[END_REF][START_REF] Azough | Concurrent La and A-Site Vacancy Doping Modulates the Thermoelectric Response of SrTiO3: Experimental and Computational Evidence[END_REF][START_REF] Wang | Large thermal conductivity reduction induced by La/O vacancies in the thermoelectric LaCoO3 system[END_REF]. For example, in perovskites (ABO3), the introduction of La-site vacancies in SrTiO3 decreases the thermal conductivity from 10 W m -1 K -1 to ~2 W m -1 K -1 and results in a glass-like behavior [START_REF] Popuri | Glass-like thermal conductivity in SrTiO3 thermoelectrics induced by A-site vacancies[END_REF][START_REF] Azough | Concurrent La and A-Site Vacancy Doping Modulates the Thermoelectric Response of SrTiO3: Experimental and Computational Evidence[END_REF].

Searching for novel thermally insulating materials, first principles calculations and highthroughput calculations have predicted an ultra-low thermal conductivity of ABO4 scheelitetype structure, composed into the stacking of weak units [AO8] and strong units [BO4] [START_REF] Najafvandzadeh | Firstprinciples study of elastic and thermal properties of scheelite-type molybdates and tungstates[END_REF][START_REF] Liu | Discovery of ABO4 scheelites with the extra low thermal conductivity through high-throughput calculations[END_REF].

In addition, the strong bonds favour a high temperature stability, while the weak bonds lead to large thermal expansion coefficients [START_REF] Ge | The thermal and optical properties of BaWO4 single crystal[END_REF] and good damage tolerance [START_REF] Najafvandzadeh | Firstprinciples study of elastic and thermal properties of scheelite-type molybdates and tungstates[END_REF][START_REF] Liu | Discovery of ABO4 scheelites with the extra low thermal conductivity through high-throughput calculations[END_REF][START_REF] Liu | Advances on strategies for searching for next generation thermal barrier coating materials[END_REF]. In particular, the low Pugh's ratio of scheelites indicate that they are quasi-ductiles [START_REF] Najafvandzadeh | Firstprinciples study of elastic and thermal properties of scheelite-type molybdates and tungstates[END_REF][START_REF] Liu | Discovery of ABO4 scheelites with the extra low thermal conductivity through high-throughput calculations[END_REF]. They are thus good candidates as TBCs.

Recently, the predictions of ultra-low thermal conductivities have been confirmed by Bsaibess et al. [START_REF] Bsaibess | Ultra-low thermal conductivity in scheelite and A-deficient scheelite ceramics[END_REF], who have reported a value around 1 W m -1 K -1 from 400 to 1000 K in BaMoO4. They have also demonstrated that the presence of vacancies on the A-site, in the La2/3□1/3MoO4 molybdate scheelite, leads to even lower thermal conductivity values of about 0.6 W m -1 K -1 over the entire temperature range [400 -1000 K] [START_REF] Bsaibess | Ultra-low thermal conductivity in scheelite and A-deficient scheelite ceramics[END_REF], in agreement with theoretical findings [START_REF] Liu | Discovery of ABO4 scheelites with the extra low thermal conductivity through high-throughput calculations[END_REF]. Based on the same calculation approach, BaWO4 should exhibit a lower thermal conductivity (0.8 W m -1 K -1 ) than BaMoO4 (1 W m -1 K -1 ) [START_REF] Liu | Discovery of ABO4 scheelites with the extra low thermal conductivity through high-throughput calculations[END_REF]. Therefore, in this study, we investigate the sintering and thermal properties of BaWO4 ceramics and A-site deficient scheelites Ce2/3□1/3WO4 and La2/3□1/3WO4.

Experimental procedure

BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics were synthesized by conventional solidstate reaction method using a stoichiometric amount of high purity precursors of BaCO3 (99.9%), WO3 (99.9%), CeO2 (99,9%) from Sigma Aldrich and La2O3 (99.9%) from ChemPur.

La2O3 was pre-heated at 1000 °C for 10 hours to remove water from this very hygroscopic precursor. Appropriate amounts of these precursors were then weighed and ground in planetary tungsten carbide ball mill at 300 rpm for 1 hour (Retsch PM 100). The obtained powders were subsequently calcined in air using alumina crucibles in a muffle furnace at 1173 K during 4 h for BaWO4 and Ce2/3□1/3WO4, and 1273 K during 10 h for La2/3□1/3WO4. The calcined powders were then ground with few drops of polyvinyl alcohol (PVA) solution (2 wt. % in water) and pressed into pellets of 10 mm in diameter and about 2 mm in thickness under a pressure of 125 MPa. The obtained pellets were heated thereafter on zirconia beads in an alumina crucible at a heating rate of 3 K min -1 , up to 773 K and then a heating rate of 1 K min -1 , up to 873 K to drive off the PVA, and sintered for 4 hours at 1573 K, 1273 K and 1323 K for BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4, respectively. Relative densities were calculated from the pellets by both geometrical measurements (mass and dimensions) and the Archimedes method using a MS204TS/00 analytical balance (Mettler Toledo) and the theoretical density values obtained by structural refinement.

X-ray diffraction (XRD) analysis was performed at room temperature on the ceramic pellets using a Bruker D8 Advance diffractometer system, with λ=1.5418 Å powered at 40 kV × 40 mA, and a scanning step of 0.02° (2θ) per second. The obtained XRD patterns were refined using JANA software in order to confirm the single-phase scheelite-structure.

Microstructures were inspected by Scanning Electron Microscopy (TESCAN MIRA 3 SEM), employing secondary electrons (SE) with an acceleration voltage of 5 kV on the fracture of ceramics covered with an ultra-thin layer of gold to avoid charging effects. The average grain size of ceramics is estimated by the linear intercept method using the image J software.

Elementary compositions were analysed by Energy Dispersive X-ray (EDX) spectroscopy, using the scanning electron microscopy (Tescan Mira 3 SEM). The homogeneity of ceramics was confirmed by back-scattering electron (BSE) analyses. Specific heat capacity (Cp) of all samples was measured by Differential Scanning Calorimetry (DSC, Netzsch STA 449 F3 Jupiter) technique. The crushed ceramics (about 50 mg) were placed in a platinum crucible and heated continuously up to 900 K under nitrogen atmosphere with a heating rate of 20 K min -1 .

Thermal diffusivity measurements of ceramics were performed by the Laser Flash method (Netzsch LFA 457 instrument), under vacuum (10 -2 mbar). All obtained samples were previously coated with a thin-layer of graphite to improve absorption of the laser light and avoid emissivity errors.

Results and discussion

The XRD patterns at room temperature of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics are presented in Fig. 1a. All the obtained peaks can be attributed to the pure scheelite-type phase of tungsten oxides. The diffraction peaks of BaWO4 reveal a tetragonal symmetry with the space group I41/a, indexed according to ICDD files (PDF cards 01-072-0746). The Ce2/3□1/3WO4 and La2/3□1/3WO4 diffractograms crystallize in a monoclinic symmetry with the space group C2/c [START_REF] Dos Passos | Structural and electrical properties of cerium tungstate: Application to methane conversion[END_REF][START_REF] Jeong | Photoluminescence features of greenemitting sol-gel synthesized La2W3O12 doped with Tb 3+ phosphor for PDP applications[END_REF]. The collected data of both compounds are in good agreement with ICDD files (PDF cards 01-085-0143 and 01-082-2068, respectively). Fig. 1b, 1c and1d show the experimental and calculated XRD patterns of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4, respectively, as well as their difference. The lattice parameters, volumes of the unit cell, theoretical and experimental densities are presented in table 1.

The Archimedes relative densities of the sintered ceramics are ≈ 97% for BaWO4 and ≈ 93% for Ce2/3□1/3WO4 and La2/3□1/3WO4. Relative densities obtained from the mass and dimensions of the sintered ceramics are ≈93%, and ≈ 90% for Ce2/3□1/3WO4 and La2/3□1/3WO4. The difference between both methods arises from the open porosity of the ceramics. Microstructure study and grain size distribution of fractured surfaces of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramic pellets imaged by Scanning Electron Microscopy are shown in Fig. 2.

The micrographs show a homogeneous microstructure and a well-developed grain morphology for all specimens. This is consistent with the measured relative density of about 97% for BaWO4 and 93% for Ce2/3□1/3WO4 and La2/3□1/3WO4. Distinct grain boundaries are observed in all samples. From histograms, the grain size of the scheelite ceramics is distributed in the range of ~ 5-50 µm. SEM images reveal average grain sizes of ~24 µm for BaWO4 ceramic and ~20 µm for Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics. Moreover, for the three ceramics, both pores and cracks are observed. The EDX analysis gives cation composition ratios of 0.98 (Ba/W) in BaWO4 and 0.68 (Ce/W and La/W) in Ce2/3□1/3WO4 and La2/3□1/3WO4. EDX measurements confirm thus the expected compositions for the three studied ceramics, within a 2% accuracy.

Back-scattering electron images show that there is no chemical contrast for the three ceramics, confirming the good homogeneity and distribution of elements. Fig. 3 shows the measurements of specific heat capacity for BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 crushed ceramics as a function of temperature, from 330 to 900 K. The specific heat of BaWO4 increases with increasing temperature from 0.34 J g -1 K -1 at 330 K to 0.46 J g -1 K -1 at 900 K. Ran et al. reported similar specific heat capacity for a BaWO4 single crystal: from 0.32±0.01 J g -1 K -1 to 0.36±0.01 J g -1 K -1 between 336 K and 573 K [START_REF] Ran | Thermal conductivity of BaWO4 single crystal[END_REF]. Specific heat capacity of Ce2/3□1/3WO4 and La2/3□1/3WO4 have been measured for the first time. Cp of Ce2/3□1/3WO4 varies from 0.34±0.01 J g -1 K -1 at 330 K to 0.46±0.02 J g -1 K -1 at 900 K. Cp of La2/3□1/3WO4 varies from 0.32±0.01 J g -1 K -1 at 330 K to 0.42±0.02 J g -1 K -1 at 900 K. They are thus similar to the values found for BaWO4, within the ±4% precision of heat capacity measurements.

The thermal diffusivity (λ) measurements of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics are shown in Fig. 4a. The thermal diffusivity of the three samples decreases when the temperature is increased from 0.588, 0.166 and 0.109 mm 2 s -1 at 373 K to 0.369, 0.106 and 0.081 mm 2 s -1 at 773 K for BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4, respectively. This decrease is due to the Umklapp scattering [START_REF] Ziman | Electrons and Phonons[END_REF]. The thermal diffusivity is slightly increasing at 873 K by 18% for Ce2/3□1/3WO4 and 15% for La2/3□1/3WO4, while it is constant for BaWO4. This is attributed to an increase of the radiative contribution at high temperatures, as reported in previous studies using the laser flash method [START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF]. Overall, it can still be seen that the A-deficient scheelites Ce2/3□1/3WO4 and La2/3□1/3WO4 exhibit very low thermal diffusivity values in the temperature range.

The thermal conductivities (κ) of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics are shown in Fig. 4b. Thermal conductivity is determined from measurements of thermal diffusivity (λ), specific heat (Cp) and density (ρ) through the following formula:

𝜅 = 𝜆 . 𝜌 . 𝐶 𝑝 (1)
The measurement of thermal conductivity was carried out three times on each studied ceramics to confirm repeatability of the results. The standard deviation has been calculated, which is

about 0.02 W m -1 K -1 .
The thermal conductivity of all samples diminishes with increasing temperature between 373 K and 673 K. It then slightly increases, most likely because of an enhanced radiative contribution that is known to play a role in laser flash measurements [START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF]. BaWO4 thermal conductivity decreases from 1.3±0.2 W m -1 K -1 to 1.0±0.1 W m -1 K -1 , which corresponds to the theoretical prediction of Liu et al. [START_REF] Liu | Discovery of ABO4 scheelites with the extra low thermal conductivity through high-throughput calculations[END_REF]. However, these values are lower than those reported by Ran et al. on a BaWO4 single crystal, which are 2.1 and 1.6 W m -1 K -1 at respectively 373 and 550 K [START_REF] Ran | Thermal conductivity of BaWO4 single crystal[END_REF]. This difference could be linked to the porosity and to the presence of microcracks and grain boundaries in the sample. To consider the impact of porosity, thermal conductivity values were normalized to represent values for 100% dense materials (κdense) using Maxwell's relation [START_REF] Winter | Oxide Materials with Low Thermal Conductivity[END_REF] as follow:

κ 100% 𝑑𝑒𝑛𝑠𝑒 = κ 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 ⨯ 1 1-1.5Ф (2)
Where Ф is the porosity.

In Fig. 4b, these corrected values are plotted for BaWO4 ceramic and still show a decrease of about 30% as compared to the single crystal. The thermal conductivity is 1.4±0.2 and 1.1±0.1 W m -1 K -1 at 373 and 550 K, respectively. This difference is attributed to the presence of grain boundaries that introduce an interface thermal resistance.

The thermal conductivity of Ce2/3□1/3WO4 decreases from 0.37±0.05 W m -1 K -1 to 0.30±0.04 W m -1 K -1 and that of La2/3□1/3WO4 is almost constant at about 0.2±0.03 W m -1 K -1 between 373 K and 673 K. These values are lower than in BaWO4 and even lower than the calculated minimum thermal conductivity (κmin) of BaWO4 [START_REF] Najafvandzadeh | Firstprinciples study of elastic and thermal properties of scheelite-type molybdates and tungstates[END_REF]. The minimum thermal conductivity can be expressed as a function of the number density of atoms and the average sound velocity, with three different models that relate to each other's as follow:

𝜅 𝑑𝑖𝑓𝑓 = 0.72 𝜅 𝐶𝑙𝑎𝑟𝑘𝑒 = 0.63 𝜅 𝐶𝑎ℎ𝑖𝑙𝑙 (3)
The main difference between these three models is that Clarke and Cahill assume propagating phonon-like vibrations, while κdiff is based on diffuson-like vibrations [START_REF] Agne | Minimum thermal conductivity in the context of: Diffuson-mediated thermal transport[END_REF]. For BaWO4, κClarke and κCahill, have been already calculated based on first-principle calculations in ref. [START_REF] Najafvandzadeh | Firstprinciples study of elastic and thermal properties of scheelite-type molybdates and tungstates[END_REF]: κClarke = 0.61 W m -1 K -1 , κCahill = 0.69 W m -1 K -1 . These values lead to κdiff = 0.44 W m -1 K -1 . The thermal conductivity experimentally measured for Ce2/3□1/3WO4 and La2/3□1/3WO4 scheelites are lower than the κmin calculated for BaWO4 whatever the model used. However, a major difference with respect to BaWO4 is the presence of a large amount of cation vacancy in these compounds that can strongly reduce the thermal conductivity, as shown previously for La2/3□1/3MoO4 deficient scheelite [START_REF] Bsaibess | Ultra-low thermal conductivity in scheelite and A-deficient scheelite ceramics[END_REF] and A-deficient ABO3 perovskites [START_REF] Popuri | Glass-like thermal conductivity in SrTiO3 thermoelectrics induced by A-site vacancies[END_REF][START_REF] Delorme | Low intrinsic thermal conductivity of Spark Plasma Sintered dense KNbO3 and NaNbO3 perovskite ceramics[END_REF][START_REF] Wang | Large thermal conductivity reduction induced by La/O vacancies in the thermoelectric LaCoO3 system[END_REF].

Another approach consists thus in modelling the impact of vacancies. Indeed, the influence of vacancies on the thermal conductivity can be estimated by considering mass-difference scattering [START_REF] Gurunathan | Analytical Models of Phonon-Point-Defect Scattering[END_REF][START_REF] Gurunathan | Alloy scattering of phonons[END_REF][START_REF] Hanus | Thermal transport in defective and disordered materials[END_REF]. We consider here a fictive material Ba2/3□1/3WO4 and calculate the change in mass on the A-site induced by vacancies, such that:

𝛥𝑀 𝐴 2 ̅̅̅̅̅̅̅ = 2 3 (𝑀 𝐵𝑎 -𝑀 𝐴 ̅̅̅̅ ) 2 + 1 3 (𝑀 𝐵𝑎 + 2 < 𝑀 ̅ >) 2 = 22306 g 2 mol -2 (4)
With < 𝑀 ̅ > the average mass of the compound, 𝑀 𝐴 ̅̅̅̅ the stoichiometry weighted average of Asite average mass, and MBa the molar mass of barium. This fictive material is close to La2/3□1/3WO4 and Ce2/3□1/3WO4 as molar masses of Ba, La and Ce are respectively 137.3, 138.9 and 140.1 g mol -1 . This leads to the average mass variance in the system < 𝛥𝑀 2 ̅̅̅̅̅̅ > normalized by the squared average atomic mass < 𝑀 ̅ > 2 equal to 1.16. It is then possible to calculate the ratio of the defective solid's thermal conductivity (Ba2/3□1/3WO4) to that of a reference pure solid (BaWO4) through Klemens model [START_REF] Klemens | The scattering of low-frequency lattice waves by static imperfections[END_REF][START_REF] Klemens | Thermal resistance due to point defects at high temperatures[END_REF]. In our case, using values from first-principle calculations for the speed of sound and the volume per atom [START_REF] Najafvandzadeh | Firstprinciples study of elastic and thermal properties of scheelite-type molybdates and tungstates[END_REF], and considering as a reference the thermal conductivity of BaWO4 we measured at room temperature (1.3 W m -1 K -1 ), we find that the thermal conductivity of the compound with vacancies would be 0.50 W m -1 K -1 , i.e.

two times less than the thermal conductivity of the sample without vacancies. Following the same reasoning, we expect the thermal conductivity of Ce2/3□1/3WO4 and La2/3□1/3WO4 scheelites to be ultra-low. In this considered mass-difference scattering model, only kinetic perturbation due to mass difference is considered for the scattering parameter. However, vacancies lead also to a force constant difference and radius difference. In addition, in some cationic deficient oxides, it has been shown that the experimental thermal conductivity is lower than the one predicted by the mass-difference scattering only, and that the influence of force constant difference and radius difference must be taken into account as well [START_REF] Gurunathan | Analytical Models of Phonon-Point-Defect Scattering[END_REF]. In the case of La1-xCoO3-x, a value of ~0.6 W m -1 K -1 is measured for x = 0.1 [START_REF] Wang | Large thermal conductivity reduction induced by La/O vacancies in the thermoelectric LaCoO3 system[END_REF]. The model with only massdifference scattering gives a thermal conductivity of 1.6 W m -1 K -1 , whereas the model with mass-difference and virial-theorem treatment for broken bonds, gives a thermal conductivity of 0.7 W m -1 K -1 which is very close to the measured one. If we assume that in scheelites, the rate of decrease is similar, it leads to a thermal conductivity of 0.2 W m -1 K -1 which is very closed to the measured thermal conductivity.

The thermal conductivity that we report for La2/3□1/3WO4 is among the lowest lattice thermal conductivity values reported for a dense crystalline oxide ceramic. As already mentioned, in the case of BaWO4, the influence of the microstructure accounts for about 30% of the decrease in thermal conductivity between the single crystal and the ceramic. If we assume a similar impact of the microstructure in La2/3□1/3WO4, this leads to an ultra-low thermal conductivity around 0.3 W m -1 K -1 for a single crystal.

Conclusions

BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 dense crystalline ceramics were prepared using the conventional solid-state reaction route. Dense ceramics have been obtained (97% for BaWO4 and 93% for Ce2/3□1/3WO4 and La2/3□1/3WO4). XRD analysis revealed a single-phase scheelitetype structure for all ceramics. The crystal structure transformed from tetragonal for BaWO4 to monoclinic for Ce2/3□1/3WO4 and La2/3□1/3WO4. The thermal measurements showed a low thermal conductivity for BaWO4, below 1 W m

Figure 1 .

 1 Figure 1. a) XRD patterns of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics at room temperature. Experimental and calculated XRD patterns of b) BaWO4 c) Ce2/3□1/3WO4 and d) La2/3□1/3WO4.

Figure 2 .

 2 Figure 2. SEM micrographs and grain size distribution of a) BaWO4, b) Ce2/3□1/3WO4 and c) La2/3□1/3WO4.

Figure 3 .

 3 Figure 3. Temperature dependence of specific heat capacity Cp of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4. Dashed lines indicate the ±4% precision of heat capacity measurements.

Figure 4 .

 4 Figure 4. Temperature dependence of a) thermal diffusivity and b) thermal conductivity of BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 ceramics. Values for 100% are corrected for the influence of the porosity. Error bars indicate the ±8% precision of thermal diffusivity measurements and ±14% precision on thermal conductivity data.

Table 1 .

 1 -1 K -1 in the investigated temperature range [373 -900 K]. In this work, ultra-low thermal conductivity values of 0.3±0.04 and 0.2±0.03 W m -1K -1 at 673 K are reported for Ce2/3□1/3WO4 and La2/3□1/3WO4, respectively. These values are among the lowest thermal conductivities reported for crystalline oxides. The results of this study confirm that such A-deficiency is an efficient approach for lowering the thermal conductivity in scheelites. Combined with chemical doping to increase the electrical conductivity, it could lead to high-performance thermoelectric materials. Refined lattice parameters, volume of the unit cell, theoretical and relative densities of sintered BaWO4, Ce2/3□1/3WO4 and La2/3□1/3WO4 scheelite ceramics.

	Compound	BaWO4	Ce2/3□1/3WO4	La2/3□1/3WO4
	a (Å 3 )	5.6288	7.8298	7.8757
	b (Å 3 )	5.6288	11.7408	11.8359
	c (Å 3 )	12.7281	11.6043	11.6539
	Cell volume (Å 3 )	403	1006	1025
	Theoretical density (g.cm -3 )	6.3	6.75	6.61
	Geometrical relative density (%)	93	90	90
	Archimedes relative density (%)	97	93	93

Acknowledgement

The authors are grateful to Tatiana Chartier for technical support.

Conflicts of Competing Interest

The authors declare that they have no conflicts of interest.


Daeyeol Kim
email: dkim@inalco.fr

d'une nouvelle société basée sur l'idéologie néo-confucéenne et d'un nouveau gouvernement, sur le modèle chinois à un grand besoin d'importation • En dehors de commerce diplomatique, l'interdiction générale par les Ming de l'exportation des ouvrages chinois

La politique d'importation

des ouvrages en chinois du roi Chŏngjo (r. 1776-1800)

Yŏngjo 英祖 (r. 1724-1776) Chŏngjo 正祖 (r. 1776-1800)

	La 1 ère moitié du 16 e siècle • Les conflits intenses entre les lettrés-fonctionnaires • La retraite des lettrés dans des régions • Le lecture des 四書 mise en valeur avec la priorité donnée à la quête de la Voie et de la culture de soi 17/05/2023 La 1 ère moitié du 17 e siècle • Les invasions manchous -Nouvelle dynastie de Qing • Une nouvelle identité : pro-Ming et anti-Qing, Chosŏn héritier de la civilisation chinoise • L'orthodoxie coréenne de l'école de Zhu Xi renforcée • L'importation croissante des ouvrages occidentaux en chinois 17/05/2023 Diversité de courants intellectuels La 2 ème moitié du 16 e siècle • Les « lettrés des forêts » devenus une force majeure de la scène politique • Le division en diverses factions des lettrés • Les guerres avec le Japon -un rapprochement avec la Chine de Ming La 2 ème moitié du 17 e siècle • Après 1683, la cour impériale Qing rassurée et confiante • Un dégel relatif entre Qing et Chosŏn au 17 e siècle • « L'idéologie était mal appliquée » à • « Il y a un problème, une révision est nécessaire » à • « Il faut aller voir ailleurs » à Evolution politique et culturelle Differences de deux rois Une circulation Les facteurs principaux Moyens/réseaux d'acquisition de la institutionnelle déterminant la nature des cour royale • L'idéologie devenue plus radicale et rigide • Le dogmatisme de 性理學 mise en cause et le retour aux 五經 et à Zhu Xi non-dogmatisé • L'Intérêt porté en dehors du confucianisme La 1 ère moitié du 18 e siècle • Les conséquences palpables des réformes et les changements dans les domaines économiques • La politique d'impartialité de roi Yŏngjo (r. 1724-1776) La 2 ème moitié du 18 e siècle • La politique d'impartialité de roi Chŏngjo (r. 1776-1800) • L'apparition des communautés chrétiennes • De nouvelles tendances dans la lecture et l'écriture littéraire confucianisme primitif 17/05/2023 7 17/05/2023 17/05/2023 • Chercher à construire dominer les discours sur les Classiques • Critiquer certaines interprétations néo-confucéennes et privilégier la vision du monde du personnelle des fonctionnaires • Rester fidèle à l'idéologie néo-fonctionnaires l'école de Zhu Xi jeunes • Les dons des individus confucénne de des belles lettres de formation des • Les dons des missionnaires occidentaux Programme spécial 燕行使 ü 抄啓文臣 • Les achats par les envoyés à Pékin hauts ü 弘文館 Collège • Les dons de la cour impériale chinoise académique et à reconnaissance royal un environnement • Chercher à obtenir ü 奎章閣 Institut ouvrages importés

Daeyeol KIM, dkim@inalco.fr UMR 8173 Chine Corée Japon (EHESS/CNRS), EA 4512 ASIEs (INaLCO) • Besoins spécifiques à la cour Chosŏn • Offres/approvisionnements de la Chine 17/05/2023

Quelques caractéristiques

La 1 ère période de son règne (1776~ 1785)

	• Les importations massives et systématiques 17/05/2023 17/05/2023 『奎章總目』 La 2 ème période de son règne (1785~1800) • Les acquisitions très faibles et occasionnelles • Les interdictions de certaines catégories d'ouvrage • En 1781, à l'ordre du roi, une catalogue établie comprenant les 華本 + 東本. • La catalogue qui nous est parvenue comprend seulement les 華本. • Le titre + une notice bibliographique • Un classement selon le système de 四部 • 697 titres, 20.179 volumes 17/05/2023 • Un fonds relativement faible en 經 • Dans la section 經 : 種數 種比率 本數 本比率 經部 78 11 % 2.222 10,7 % 史部 134 18,9 % 4.201 20,2 % 子部 182 25,7 % 8.841 42,4 % 集部 315 44,4 % 5.573 26,7 % 計 709 20.837 17/05/2023 部 類 種數(%) 本數(%) 經 總經 7 (9) 966 (43,5) 易 7 (9) 73 (3,3) 書 (6,4) 66 (3) 詩 (6,4) 63 (2,9) 春秋 7 (9) 58 (2,6) 禮 (12,8) 397 (17,9) 樂 (2,6) 16 (0,7) 四書 (19,2) 243 (10,9) 小學 (25,6) 340 (15,3) 計 9 78 2.222 史 正史 (20,2) 1215 (28,3) 編年 (11,9) 556 (12,9) 別史 (35,8) 915 (21,3) 掌故 (11,2) 867 (20,2) 地理 (16,4) 553 (12,9) 抄史 (1,5) 117 (2,7) 譜系 (0,8) 36 (0,8) 總目 (2,2) 42 (1) 計 8 4.201 部 類 種數(%) 本數(%) 子 儒家 47 (25,8) 685 (7,6) 天文 1 (0,6) 10 (0,1) 曆籌 9 (5) 159 (1,8) 卜筮 1 (0,6) 4 (0,1) 農家 2 (1,1) 27 (0,3) 醫家 9 (5) 135 (1,5) 兵家 9 (5) 136 (1,5) 刑法 3 (1,7) 46 (0,5) 道家 6 (3,3) 45 (0,5) 釋家 3 (1,7) 49 (0,6) 雜家 13 (7,1) 63 (0,7) 說家 23 (12,6) 238 (3) 藝玩 15 (8,2) 155 (17,5) 類事 32 (17,6) 6.409 (72,5) 叢書 9 (5) 680 (7,7) 計 15 182 8.841 集 總集 80 (26,4) 2.125 (43,2) 別集 223 (73,6) 2.790 (56,8) 計 2 315 5.573 17/05/2023 『內閣訪書錄』 • Une catalogue établie en vue d'une acquisition par l'Institut royal 奎章閣 • Difficile de dater. Mais probablement achevée juste après le 『奎章總目』(1781) • Un classement selon le système de 四部 • 385 titres, 10.357 volumes 17/05/2023 • 『浙江採集遺書總錄』 , 鍾音(淸) 等受命編, impression Choson 乾隆39年 (1774) • 『直齋書錄解題』 陳振孫(宋) 撰, impression Choson 乾隆 39年 (1774) • Probablement aussi 『 四庫全書簡明目錄 』 17/05/2023 • Diversité et quantité augmentée en 經 • Dans la section 經 : -L'importance en 類事, 醫家, 兵家 -L'existence de fonds de 道家 et 釋家 17/05/2023 『內閣訪書錄』 收錄書籍分析表 種數 種比率 本數 本比率 經部 134 34,8 % 2,263 21,8 % 史部 63 16,6 % 2,646 25,5 % 子部 124 32,2 % 2.943 28,4 % 集部 63 16,4 % 2,505 24,2 % 計 385 10,357 17/05/2023 部 類 種數(%) 本數(%) 經 易 23 (17,2) 403 (17,8) 書 19 (14,2) 248 (11) 詩 24 (17,9) 512 (22,6) 禮 24 (17,9) 593 (26,2) 春秋 17 (12,7) 401 (17,7) 四書 6 (4,5) 79 (3,5) 孝經 1 (0,7 4 (0,2) 總經 4 (3) 191 (8,4) 樂 6 (4,5) 208 (9,2) 小學 10 (7) 191 (8,4) 計 10 134 2.263 史 正史 1 (1,5) 172 (6,5) 編年 4 (6) 237 (9) 別史 2 (3) 330 (12,5) 雜史 2 (3) 41 (1,5) 掌故 28 (41,8) 1.014 (38,3) 地理 22 (32,8) 764 (28,9) 譜系 8 (11,9) 88 (3,3) 計 7 67 2.646 部 類 種數(%) 本數(%) 子 儒家 (11,6) 202 (6,7) 天文 (1,7) 29 (1) 曆籌 (2,5) 102 (3,5) 農家 (1,7) 109 (3,7) 醫家 (14,9) 446 (15,2) 兵家 (10,7) 177 (6) 道家 (2,5) 128 (4,3) 釋家 (2,5) 20 (1,7) 雜家 6 (5) 229 (7,8) 說家 (4,1) 140 (4,8) 藝玩 (12,4) 272 (9,2) 類事 (17,4) 740 (25,1) 叢書 10 (8,3) 349 (11,9) 計 13 2.943 集 總集 12 (19) 944 (37,7) 別集 51 (81) 1561 (62,3) 計 2 63 2,505 『內閣訪書錄』 收錄書籍分析表 17/05/2023 28 部類 類屬 計 總計 部類 類屬 計 總計 經部 134 子部 124 易 23 儒家 14 書 19 雜家 28 詩 24 類書 禮 24 小說 春秋 17 藝術 四書 6 譜錄 11 孝經 1 術數 總經 4 天文算法 樂 6 史部:地理 小學 10 兵家 10 史部 63 農家 編年 3 醫家 17 別史 2 道家 載記 2 釋家 政書 23 集部 63 職官 12 總集 12 地理 14 別集 51 譜系 7 Evolution de 奎章閣 所藏 華本 • Après 1780, relativement peu d'importation par rapport à l'acquisition/publication des ouvrages coréens 17/05/2023 29 華本 1781 1870 傾 差 題目數 697 756 +59 冊數 20.179 22.600 +2421 華本 + 東本 1780 1795 冊數 30.000 80.000 奎章總目 (1781) 內閣訪書錄 閱古觀書目 (1870?) 種數 比率 種數 比率 種數 比率 經 78 11,2 % 134 34,8 % 111 14,6 % 史 134 19,2 % 63 16,6 % 144 18,6 % 子 182 26,1 % 124 32,2 % 189 24,8 % 集 303 43,5 % 63 16,4 % 317 41,7 % 計 697 100,0 % 385 100,0 % 761 100,0 % 17/05/2023 Les titres acquis ou en commun entre 『內閣訪書錄』 et 『閱古觀書目』 經 部 『古周易』, 『 春秋辨疑』, 『 漢隸字源』, 『 廣金石韻府』 子 部 『 廣博物誌』, 『 昨非菴日纂』, 『 香乘』, 『 翰苑新書全集』, 『 昭代叢書』, 『 檀机叢書』, 『 玉機微意』 集 部 『 誠齋集』 17/05/2023 Une très faible importation, pourquoi ? • Epuisement ou interdiction en Chine? • Remplacement ? • Changement de politique de la cour ? 17/05/2023 Les évènements en 1785 et 1791 Les tensions dues à l'introduction du catholicisme • La découverte à Séoul d'un mouvement catholique -1785 • Le procès de Chinsan -1791 : l'incinération par un yangban catholique de la tablette ancestrale de sa mère La campagne du « retour à la littérature correcte » -1971 • Les styles d'administration 科文 • Les histoires romancées 稗官雜記 • Le style de « notes au fil du pinceau » 筆記 17/05/2023 L'acquisition après le 『內閣訪書錄』 1794 • Ouvrages sur Confucius -『闕里志』 -『 闕里文獻考』 -『 聖廟圖』 -『 孔氏碑本』 1799 • Environs 200 volumes de 方書 ainsi que 『律曆淵源』nécessaires à 觀象監 -(5/30) • Autres ouvrages -(11/17) -『 朱子大同集 』 -『 朱子實紀 』 -『 後漢書』 17/05/2023 34 1796 • 66 volumes de 方書 acquis et offerts à la cour par les fonctionnaires hémérologues Les projets d'importation 1798 • L'ordre d'acquisition : ouvrages nécessaires au bureau d'observatoire 觀象 監, ex. 『律曆淵源』, 『協 紀辨方書』-10/12 1799 • L'ordre d'acquisition : 朱子諸書 -/07/16 • L'intention d'acquérir des ouvrages concernant les principes de 數理 et 曆象 17/05/2023 Les interdictions d'importation • 西洋之書 (正祖 9年-1785, 4月 9日) • 不經書籍 (正祖 10年-1786, 1月 22日) • 天主妖術 (正祖 11年-1787, 4月 27日) • Une discussion à la cour sur l'interdiction des « 稗官雜記等册 » (1791/10/25, 日省錄) • 稗官小記姑無論, 雖經書、史記, 凡係唐 板者 (正祖 16年-1792, 10月 19日) 17/05/2023 Les destructions des ouvrages occidentaux • 1791 -« 弘文館所藏西洋諸書… 令館中燒火 » -27 titres de 外奎章閣 brûlés dont la plupart sont liés au catholicisme • Parmi les ouvrages occidentaux dans le 『奎章總目』, les ouvrages disparus dans la catalogue ultérieure : -『記法』 -『西儒耳目資』 Ouvrages occidentaux détruits en 1791/12 de 外奎章閣 滌罪正規 悔罪要指小引 玫瑰十五端 渡海苦績紀 聖記百言 天主降生言行紀略 齋克 主制群徵小引 達道紀言 天主聖敎四末論 西學修身 聖水紀言 西學齊家 進呈書像 勵學古言 仁會約 斐錄答彙(匯答?) 西洋統領公沙效忠記 童幼教育 靈魂道體說 泰西人身槪說 淸凉山志 主敎緣起總論 寰宇始末 畏天愛人極論 眞福訓詮總論 譬學 悔罪要指小引 17/05/2023 Conclusion • Peu d'ouvrages chinois contemporains importés • Sauf quelques éditions rares sur Confucius et Zhu Xi • Peu d'ouvrages occidentaux importés • Sauf les ouvrages sur le calcul, l'astronomie et l'hémérologie 17/05/2023 Quelques explications

• : l'ordre d'acquisition de 『 四庫全書 』 • : l'acquisition de 『古今圖書集成』 • : l'acquisition de plusieurs dizaines de titres rares dont -『通志堂經解』de 徐乾學, 477 volumes -『繹史』de 馬繡 , 36 volumes Un plan d'acquisition en 1781 ? • La catalogue 奎章總目 • La liste d'ouvrages de 『古今圖書集成』 • La catalogue 內閣訪書錄 • Un rassemblement des fonds de : -弘文館 藏本 -江華府 行宮 所藏 圖書 -『古今圖書集成』 -Acquisitions par 奎章閣 閣臣 • 30.000 volumes env. (華本 + 東本) en 1780 • 80.000 volumes env. (華本 + 東本) en 1795 -L'importance de 四書 et 小學

• Dans la section 子 :

-L'importance de 類事 (圖書集成 5.022 volumes) -Le fonds faible en 兵家 -L'existence de fonds de 道家 et 釋家

『 奎章總目 』 收錄書籍分析表

-L'importance en 五經 -La faiblesse en 四書 et 小學

• Dans la section 史 :

-L'importance en 掌故

• Dans la section 子 :

•

  Grandes collections, encyclopédies et ouvrages scientifiques et techniques déjà en possession • Publications et rééditions coréennes en projet • La politique de « restauration de la tradition correcte » • La politique culturelle et scientifique indépendantiste vis-à-vis de la Chine de Qing • La crise due à l'introduction du catholicisme • Une conjonction du marché chinois de publication ?

17/05/2023

17/05/2023