Jiao Zhang

Yang Li

Chen Zhang

Feifei Chen
email: chenfeifei1@nbu.edu.cn

Xianghua Zhang

Wei Ji

Glass forming region and optical properties of chalcogenide glasses within a gallium-tin-selenium ternary system

Keywords: Selenide chalcogenide glasses, Ga-Sn-Se system, glass forming region, optical properties

In this work, glass forming region of arsenic-and germanium-free chalcogenide glasses (ChGs) within a gallium-tin-selenium (Ga-Sn-Se, GSS) ternary system is depicted. Seven representative compositions in the glass forming region are selected, and the corresponding bulk GSS glass samples are prepared for characterizing the optical properties. The experimental results show that the GSS ChGs have a wide transparent window from ~1 to 20 μm and low dispersion at both 3-5 μm and 8-12 μm mid-infrared windows. The dependence of optical bandgap energy (Eopg) on mean coordination number (MCN) indicates the existence of medium-range interactions in the GSS glass network, and its origin is investigated by the Raman spectra.

Introduction

Chalcogenide glasses (ChGs) have the highest third-order optical nonlinearity (TONL) in all optical glass materials, and they also possess ultra-wide infrared (IR) transmission windows as well as low phonon energy, high linear refractive index and low thermal refractive index coefficient, which make ChGs a perfect candidate for both IR and nonlinear photonic devices, especially all-optical switching, optical frequency comb, supercontinuum generation [START_REF] Dai | A review of mid-infrared supercontinuum generation in chalcogenide glass fibers[END_REF][START_REF] Du | Chip-scale broadband spectroscopic chemical sensing using an integrated supercontinuum source in a chalcogenide glass waveguide[END_REF][START_REF] Wang | All-optical switching in long-period fiber grating with highly nonlinear chalcogenide fibers[END_REF][START_REF] Lemière | Mid-infrared supercontinuum generation from 2 to 14 μ m in arsenic -and antimony-free chalcogenide glass fibers[END_REF][START_REF] Li | Materials selection and mechanism of non-linear conduction in chalcogenide selector devices[END_REF].

In the past few decades, ChGs based on germanium (Ge)-chalcogen and arsenic (As)-chalcogen systems have been intensively studied for their excellent glass forming ability, wide IR transparent windows and high thermal stability [START_REF] Ghayebloo | The relationship between structural and optical properties of Se-Ge-As glasses[END_REF][START_REF] Abbady | Thermal stability and crystallization kinetics of[END_REF][8][START_REF] Pradhan | Quantification of nonlinear absorption in ternary As-Sb-Se chalcogenide glasses[END_REF][10][START_REF] Wei | Structural, thermal and optical properties and transition threshold in Ge-Sb-Se glassy system[END_REF].

However, considering the high price of Ge and toxicity of As, ChGs in As-and Ge-free systems with high optical performance are also in great demand, but very few studies can be found besides the gallate ChGs based on Ga-La-S ternary system [START_REF] Zhou | Two-photon absorption and nonlinear refraction of lanthanum sulfide-gallium sulfide glasses[END_REF][START_REF] Ravagli | Ga-La-S-Se glass for visible and thermal imaging[END_REF][START_REF] Ravagli | Structural modification of Ga-La-S glass for a new family of chalcogenides[END_REF] despite its preparation process is much more complex than the conventional ChGs. Recently, Yang et al. [START_REF] Yang | Ga-Sb-S chalcogenide glasses for mid-infrared applications[END_REF][START_REF] Qiu | Sb2S3-CsI[END_REF] reported the glass forming ability of gallate sulfide ChGs based on Ga-Sb-S ternary system and found large TONL of the ChGs as well as expanded IR transmittance region compared to Ge-or As-based sulfide ChGs, which gives the society of ChG materials new insight into the development of novel gallate ChGs with similar preparation process but better properties as compared to the conventional ChGs.

On the other hand, considerable recent studies with respect to chalcogenide photonic devices [START_REF] Zhou | Large nonlinearity and low loss Ge-Sb-Se glass photonic devices in near-infrared[END_REF][START_REF] Li | Reverse-strip-structure lift-off[END_REF] have been focused on selenide ChGs which possess wider IR transmittance region and larger TONL properties as compared the sulfide ChGs.

A c c e p t e d m a n u s c r i p t

Additional, our prior studies [START_REF] Lin | Midinfrared optical properties of chalcogenide glasses within tin-antimony-selenium ternary system[END_REF][START_REF] Xue | the Sn-Sb-Se ternary system[END_REF] have discovered that the incorporation of tin (Sn) to selenide ChGs could significantly enhance the TONL properties and eliminate impurity absorption. Therefore, it would be an interesting subject to elaborate on Sn contained gallate selenide ChGs, i.e. gallium-tin-selenium (Ga-Sn-Se, GSS) ternary system glasses, which maybe a green/sustainable and low-cost ChG system comparing with the As-and Ge-based ChGs. However, to the best of our knowledge, ChGs in GSS ternary system remain unexplored, which motivates us to conduct the corresponding research. Accordingly, the goal of this paper is to give the glass forming region of the GSS ternary system as well as the properties of the GSS ChGs, and to elucidate the correlation to their network structure.

Experiment

A set of chemical compositions in Ga-Sn-Se ternary system were designed for exploration of the corresponding glass forming region, the specific data are given in supplementary materials. 10 g of analytical reagent gallium, tin and selenium as raw materials were weighed according to the elemental ratio and mixed in a quartz tube (Φ10 mm). The quartz tube containing the raw material was pre-heated at 100 °C for 4 h to remove moisture from the quartz tube and the raw material which was then sealed under vacuum (10 -4 Pa) and melted in a rocking furnace. The melting temperature of the samples was set at 900 °C and maintained for 12 hours to ensure sufficient reaction of the raw materials. After that, the tube was rapidly quenched in water to form ingot. For the glass samples applied for further properties testing, the corresponding ingots were annealed at a temperature of 20 °C below the glass transition temperature (Tg) for 6 hours to minimize internal stress and slowly cool to room temperature at a rate of 10 °C/h. For optical properties testing, the glass ingots were then cut and polished to the plate with thickness of 1 mm ± 0.02 mm which gave A c c e p t e d m a n u s c r i p t rise to the main error of ± 1% in calculation of optical bandgap energy (Eopg) of the glass samples.

To identify nature of the obtained fusions, X-ray diffractometer (D2 phaser, Bruker, Germany) was used, and the samples with sharp diffraction peaks were identified as crystalline. About 10 mg powder was sealed into an aluminum pan for Tg and Tx measurements using a differential scanning calorimeter (DSC, TA Q2000, USA), and the instrumental error is ± 1 °C. The thermal stabilit y par ameter Δ T calculated by Tg and Tx has an error of ± 2 °C. Transmission spectra of the re-prepared samples in wavelength range from 0.4 to 2.5 μm were recorded by a UV-VIS-NIR spectrophotometer (Lamda 950, Perkin-Elmer, Waltham, MA) and wavelength range from 2.5 μm to 25 μm were recorded by a Fourier transform IR (FTIR) spectrometer (Nicolet381, Nicolet, USA). The samples with flat transmittance above 50% were identified as glass, otherwise partial crystalline. Authentic molar percentage of each elements in the GSS ChGs was determined by energy-dispersive spectrometry (EDS, XFlash Detector 410-M, Bruker, Germany), and the instrumental error is ± 1%. Density (d) was measured using Archimedes method and each d is average of eight measurements with instrumental errors of ± 0.001 g/cm 3 .

Linear refractive index (n0 in wavelength range from 1.7 to 20 μm) of the GSS ChGs was estimated using an IR variable angle spectroscopy ellipsometer with a precision of ± 0.005 (IR-VASE Mark II, J.A. Woollam, USA), where the angles of incident were selected 65° and 75°, respectively, and spectral resolution was 16 cm -1 . Thus, the calculated results of partial dispersion v3-5 and v8-12 had approximately ± 1% error which is three-fold to that of the n0 value. Raman spectra of the glasses were recorded using a Renishaw Invia Raman microscope (Renishaw Invia, Gloucestershire, UK) with an excitation wavelength of 785 nm and frequency A c c e p t e d m a n u s c r i p t of each structural unit by Gaussian decomposition of Raman spectrum is about ± 5%, which is within acceptable limits.

All the above tests were conducted at room temperature.

Results

Fig. 1 shows the glass forming region of the GSS ChG system, and nature of the ingots prepared from each molar composition are also given in supplement material. It can be seen from Fig. 1 that the GSS ternary system has a small glass forming region located in Se-rich region which is composed of ~65%-80% Se, ~5%-15% Ga, and ~15%-25% Sn, meaning that the compositions in both stoichiometry and Sedeficiency are not able to keep the bulk in amorphous state. As presented in Table 1, seven compositions in glass forming region were employed to represent the general properties of ChGs in the GSS system. Fig. 2(a) shows the XRD patterns of the selected seven samples, the absence of sharp diffraction peaks in the pattern clearly illustrates that the selected GSS compositions were amorphous. For comparison, Fig.

2(b)

shows the XRD patterns of two compositions (Ga10Sn15Se75 and Ga5Sn10Se85) out of the glass forming region, which were identified as partially crystalline by the presence of diffraction peaks belonging to Ga2Se3 phase (JCPDF No. 5-724).

The measured molar composition of the seven GSS specimens by EDS are given in Table 1, and they are generally in consistent with the nominal ones. The main deviation of the measured composition from the nominal is slight loss of Sn content, that's probably because of the precipitate of Sn atoms that have much larger size and weight than the Ga and Se atoms. Glass transition temperature (Tg) and crystallization temperature (Tx) of the GSS ChGs as given in Table 1. It can be seen that the Tg value increased by over 80 o C when Se was replaced by both Ga and Sn. Since Tg of glass resolution of ± 0.15 cm-1. The calculation error of the proportion of the integral area A c c e p t e d m a n u s c r i p t materials is determined by average bond energy and connectedness of the glass network [START_REF] Tichý | Covalent bond approach to the glass-transition temperature of Ge28Sb12Se60 chalcogenide[END_REF][START_REF] Saffarini | Thermal stability and percolation threshold of Ge-Se-Fe glasses[END_REF], substitution of homopolar bonds (Se-Se bond: 183.9 kJ/mol) by heteropolar bonds (Sn-Se bond: 198.5 kJ/mol, Ga-Se bond: 271.7 kJ/mol) [START_REF] Giridhar | Chemical ordering in Ge-Ga-Se glasses[END_REF][START_REF] Wang | Effect of SnI2 on the thermal and optical properties of Ge-Se-Te glasses[END_REF] that have larger bond energy is accounted for the increased Tg in ChGs with higher Ga and Sn content. Besides, calculation of thermal stability parameter ∆T = (Tx -Tg)

shows that increasing content of Ga which increased Tg would reduce total thermal stability of the GSS ChGs. Sample GSS1 with lowest Ga content have the largest ∆T, and the value near 150 o C indicating that this composition is suitable for fiber drawing.

Further, as given in Table 1, Tg of the GSS samples (GSS5~7) is comparable to that of the Ge-Sb-Se and Ga-Sb-S ChGs, and much higher than that of the As40Se60 ChG.

As the optical transmission spectra shown in Fig. 3 ChGs, due to lower reflection loss originated from the smaller refractive index (n0, given in Table 2) of the GSS ChGs.

v S-L  n M 1 n S n L (1)
in which S and L refer to short and long wavelength of interests respectively, and M is the wavelength in the middle of them. The calculated data are shown in

Discussion

In order to find correlation between molar composition and optical properties of the GSS ChGs, the constraints model using mean coordination number (MCN) as a fundamental metric is applied. According to the authentic molar percentage of each ChG given in Table 1, the MCN value can be calculated by the following equation [START_REF] Srinivasan | Observation of a threshold behavior in the optical band gap and thermal diffusivity of Ge-Sb-Se glasses[END_REF]:

MCN  xCN Ga yCN Sn zCN Se x y z (2)
where x, y and z are molar percentage of Ga, Sn and Se respectively, and CN is their coordination number. Since the all the GSS specimens have Se-rich compositions, both Ga and Sn atoms would be 4-fold coordinated [START_REF] Giridhar | Chemical ordering in Ge-Ga-Se glasses[END_REF][START_REF] Imran | Glass transition kinetics and optical band gap in Se85-xSb15[END_REF] layered structures in ChG network [START_REF] Tanaka | Structural phase transitions in chalcogenide glasses[END_REF]. By plotting the Eopg of the GSS ChGs as a function of the MCN as shown in Fig. 6, the Eopg values exhibit a general decreasing tendency with increase of MCN, while two abnormal points (i.e. rising of Eopg) at MCN = 2.55 and 2.65 can be observed as well. Such behavior can be attributed to the normal structural evolution with molar compositions in combination with the occurrence of medium-range interactions among the structural units in GSS glass network. Therefore, Raman spectra of the seven GSS samples are measured in order to uncover the structural evolution that accounts for the MCN-dependent optical properties as well as the medium-range interactions in GSS ChGs. In general, as the spectra shown in Fig. 7, it can be seen that the GSS ChGs have general Raman signal in frequency range from 150 to 300 cm -1 . The main Raman peak located at ~180 cm -1 belongs to vibration mode of Sn-Se heteropolar bonds in [SnSe4] tetrahedral units [START_REF] Lin | Midinfrared optical properties of chalcogenide glasses within tin-antimony-selenium ternary system[END_REF] which built up the main frame of the GSS glass network. The secondary peak located at 260 cm -1 belongs to the vibration mode of the Se-Se bonds in Se8 rings [START_REF] Qiao | A c c e p t e d m a n u s c r i p t Correlating structure with threshold behavior of chalcogenide glasses within Ge-Sn-Se ternary system[END_REF], and it is remarkably broad which indicates that the Se8 rings are highly amorphous and they keep the GSS network in non-crystalline state.

By using the Gaussian decomposition method as illustrated in Fig. 8(a), each Raman spectrum can be decomposed into five Gaussian bands corresponding to vibration mode of structural units in the GSS glass network. According to the results in previous literature, assignment of the five Gaussian bands can be: [Se3Ga-GaSe3] ethane-like units with central frequency at ~173 cm -1 [START_REF] Tang | Micro-structural studies of GeSe2-Ga2Se3-MX (MX=CsI and PbI2) glasses using Raman spectra[END_REF][START_REF] Tang | Preparation and properties of GeSe2-Ga2Se3-KBr new chalcohalide glasses[END_REF], symmetric stretching of tetrahedral [SnSe4] at ~180 cm -1 , symmetric stretching of tetrahedral [GaSe4] at ~193 cm -1 [START_REF] Pethes | Short range order in Ge-Ga-Se glasses[END_REF], and bending and stretching of [Se8] rings at ~230 cm -1 and ~258 cm -1 [START_REF] Adam | Infrared and Raman studies on Snx-Sb5-Se95-x chalcogenide glasses[END_REF] respectively, which are tabulated in Table 3. To give the quantized information about the structural changing of the GSS network, proportion of the integral area of each units that consist of Ga-Se heteropolar bonds which are strong bonds (bonding energy of 271.7 kJ/mol) in GSS network energy, as can be observed in Fig. 8(b). Furthermore, the proportions of [Se3Ga-GaSe3] and [GaSe4] units exhibit a reversed trend when the MCN value passes 2.55, indicating that the [GaSe4] tetrahedrons have started to agglomerate and cross-link with each other by Ga-Ga homopolar bonds at this threshold MCN, and such behavior can be regarded as medium-range interactions [START_REF] Wei | Correlation between structural and physical properties in Ge-Sb-Se glasses[END_REF],

which resulted in reduction of the total bond energy but enhancement of the network flexibility of the GSS ChGs. Consequently, the conversions of [GaSe4] tetrahedrons to [Se3Ga-GaSe3] units at MCN > 2.55 leads to significant decrease of Eopg value, while the transition temperature (Tg) and linear refractive index (n0) (as given in Table 1) of the GSS ChGs exhibits a completely reversed tendency. Besides, it should be noted that proportion of the integral area of [Se3Ga-GaSe3] at MCN = 2.69 has reached 34% which is larger than that of [Se8] (30%) and [SnSe4] (22%), indicating that the [Se3Ga-GaSe3] ethane-like units had become the main frame of the GSS glass network after experiencing the maximum level of medium-range interactions.

Conclusion

Glass forming region of arsenic-and germanium-free chalcogenide glasses (ChGs) within a gallium-tin-selenium (Ga-Sn-Se, GSS) ternary system is explored, and the glass forming region is found at Se-rich region in which is composed of

  (a), all the GSS ChGs exhibit flat transmittance window range from ~1 to 20 μm, and they are optically transparent even beyond 25 μm. Since the raw materials were not purified, impurity absorption[START_REF] Snopatin | High-purity chalcogenide glasses for fiber optics[END_REF] due to O-H, Se-H, H2O, Ga-O and CO2 can be observed at 2.9 μm, 4.5 μm, 6.3 μm, 9.5 μm and 15 μm respectively. No impurity absorption from Sn-O is observed since it is beyond 20 μm[START_REF] Wang | Effect of SnI2 on the thermal and optical properties of Ge-Se-Te glasses[END_REF] and overlapped by the harmonic intrinsic vibrations of the components. Fig.3(b)shows the comparison of IR transmittance region of the sample GSS1 and the commercial As40Se60 and Ge20Sb15Se65 selenide ChGs with the same thickness of 1 mm, and it is clear that the GSS ChG possess extended IR transmittance range: the long-wavelength cut-off of sample GSS1 red-shifted by 3.2 μm and 1.3 μm compared to that of the Ge20Sb15Se65 ChG (cut-off at 16.5 μm) and As40Se60 ChG (cut-off at 18.4 μm) respectively. Furthermore, transmittance of GSS ChGs (> 70%) is remarkably higher than those of both As40Se60 and Ge20Sb15Se65

  photon energy of wavelength at linear absorption coefficient is 100 cm -1 can be used

A c c e p t e d m a n u s c r i p t

A c c e p t e d m a n u s c r i p t structural unit was

  Fig. 8(b). It can be found that only the [Se3Ga-GaSe3] units exhibit a monotonic

A c c e p t e d m a n u s c r i p t

  On the other hand, as shown in Fig.8(b), proportion evolution of the [Se8] rings (including both bending and stretching modes) with MCN value exhibit a completely reversed trend to the tetrahedral [SnSe4], indicating they have a competitive relationship in the GSS network. At MCN = 2.65, the substitution of [Se8] rings by[SnSe4] tetrahedral reaches the maximum level, parallels the sudden rising of Eg value at the same MCN as seen in Fig.6. Accordingly, the second abnormal Eopg point at MCN = 2.65 can be attributed to substitution of the weak Se-Se homopolar bonds (bonding energy of 183.9 kJ/mol) by the strong Sn-Se heteropolar bonds (bonding energy of 196.9 kJ/mol) in GSS network with medium-range interactions.

~65-

  80% Se, ~5-15% Ga, and ~15-25% Sn. Transition temperature (Tg) of GSS ChGs varied from 182 to 266 o C is mainly determined by Ga content, and the GSS ChG with best thermal stability was obtained from composition with lowest Ga content (Ga5Sn20Se75). GSS ChGs exhibit flat transmittance window range from ~1 to 20 μm, and dispersion of the ChGs at 3-5 μm mid-IR window is slightly smaller than the dispersion at 8-12 μm mid-IR window. GSS glass network consist of tetrahedral [SnSe4], tetrahedral [GaSe4], [Se3Ga-GaSe3] ethane-like units and [Se8] rings, and the structural changing with increase of mean coordinated number (MCN) can be described in term of cross-linking of tetrahedral [GaSe4] by [Se3Ga-GaSe3] ethanelike units and mutual substitution of [Se8] rings and tetrahedral [SnSe4]. Relationship between optical bandgap energy (Eopg) and MCN value of the GSS ChGs indicates that medium-range interactions started from GSS glass network with MCN A c c e p t e d m a n u s c r i p t = 2.55, in consistent with the constrained model based on covalent bonding network, and the increasing number of cross-linked [Se3Ga-GaSe3] ethane-like units is the origin for such behavior.

A c c e p t e d m a n u s c r i p t A c c e p t e d m a n u s c r i p t

A c c e p t e d m a n u s c r i p tFigureFig. 1 .

 1 Figure

A c c e p t e d m a n u s c r i p t

Fig. 2 .

 2 Fig. 2. (a) XRD patterns of GSS samples; (b) identification of the crystal phases in crystallized sample with molar composition of Ga10Sn15Se75 and Ga5Sn10Se85.

A c c e p t e d m a n u s c r i p t

Fig. 3 .

 3 Fig. 3. (a) Full-band transmission spectra of the GSS glasses as well as the notification of impurity absorption; (b) Comparison of FTIR spectra between Ge20Sb15Se65, As40Se60 ChGs and a GSS sample (GSS1) with the same thickness of 1 mm.

Fig. 4 .

 4 Fig. 4. Near infrared absorption spectra of the GSS ChGs.

Fig. 5 .Fig. 6 .

 56 Fig. 5. Linear refractive index and its infrared dispersion curves of the GSS ChGs. A c c e p t e d m a n u s c r i p t

Fig. 7 .

 7 Fig. 7. Normalized Raman spectra of the GSS glasses.

A c c e p t e d m a n u s c r i p t

Fig. 8 .

 8 Fig. 8. (a) Decomposition of each Raman spectrum of the GSS ChGs; (b) Proportion of integral area for each Gaussian peak in (a) as a function of MCN.

A c c e p t e d m a n u s c r i p t

  Click here to download Supplemental material for on-line publication only: supplement material.docx A c c e p t e d m a n u s c r i p t

Table 2

 2 of the ChGs is weaker at the first MIR window. v3-5 and v8-12 values of GSS5 are the smallest meaning that this sample has the strongest dispersion in MIR account for its largest n0; GSS2 has relatively larger v3-5 and v8-12 value for its smallest n0.

	m a n u s c r i p t
	A c c e p t e d

, most of the GSS ChGs have v3-5 value larger than v8-12 value, which means that dispersion

Table Tables Table 1

 Tables1 Compositions, characteristic temperatures and other physical parameters of the GSS ChGs as well as the ChGs in previous reports for references.

	Label GSS1 GSS2 GSS3 GSS4 GSS5 GSS6 GSS7	Measured Composition (±1% ) Ga Sn Se 4.23 16.75 10.78 14.48 11.36 15.99 12.56 16.98 12.77 19.73 11.07 20.83 16.11 18.21 Ge 20Sb15Se65 Nominal Composition Ga 5Sn20Se75 Ga 10Sn16Se74 Ga 10 Sn 17.5 Se 72.5 Ga 10 Sn 18.5 Se 71.5 Ga 10Sn20Se70 Ga 10 Sn 22.5 Se 67.5 Ga 15Sn20Se65 As40Se60 m a n u s c r i p t Tg Tx d ∆T ( o C) ( o C) o C) (g/cm 3 ) MCN ±1 ±1 ±2 ±0.001 79.02 183 329 146 4.706 2.42 74.74 182 277 95 4.672 2.51 72.65 185 283 98 4.699 2.55 70.46 196 295 99 4.725 2.59 67.50 254 327 73 4.810 2.65 68.10 255 336 81 4.797 2.64 65.68 266 319 53 4.815 2.69 285 --4.72 2.55 182 --4.63 2.40
	Ga 9Sb31S60 [15] A c c e p t e d	244	342	98	4.03	2.49

Table 2

 2 Optical parameters of the GSS ChGs as well as the ChGs in previous reports for reference.

	Sample	E opg (eV)	n0 (±0.005)	3-5	v 8-12
			v
				(±1%) (±1% )
	GSS1	1.62		148.00	146.40
	GSS2	1.61		164.11	146.30
	GSS3	1.63		134.82	133.27
	GSS4	1.59		136.45	123.50
	GSS5	1.58		117.38	94.00
	GSS6	1.56		151.40	115.15
	GSS7	1.53		117.15	100.07
	Ge 20Sb15 Se65	1.70		170.8	99.1
	As40Se60	1.63		166.3	157.5
	Sn10Sb20Se70 [19]	1.03		93.1	96.5

Table 3

 3 Assignments of the decomposed Raman bands to the structural units in GSS glass network.

	Wavenumber (cm -1 )	Assignments
	165~175	[Se3Ga -GaSe3] ethane-like units
	180~1 82	[SnSe4] tetrahedrons
	188~1 94	[GaSe4] tetrahedrons
	230~2 36	[Se8] rings (bending)
	258	[Se8] rings (stretching)

Acknowledgements

This work was partially supported by the National Key Research and Development Program of China (grant no. 2016YFB0303803), National Natural Science Foundation of China (grant no. 61675106) and Natural Science Foundation of Zhejiang Province (grant no. LY19F050005). It was also sponsored by K.C. Wong Magna Fund in Ningbo University. Credit Author Statement Jiao Zhang, Formal analysis, Writing -Original Draft, Writing -Review & Editing, Visualization. Yang Li, Investigation, Methodology. Chen Zhang, Investigation. Feifei Chen, Conceptualization, Formal analysis, Writing -Review & Editing, Funding acquisition, Supervision. Xianghua Zhang, Conceptualization, Supervision.

Wei Ji, Conceptualization, Supervision.

Conflict of interest form

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.

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Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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