Synthesis, dopant solubility, and thermostructural properties of Ca_10.5−xTM_x(VO₄)₇ (TM = Co, Cu) as function of transition metal content

Houri S. Rahimi Mosafer *^a, Wojciech Paszkowicz ^a, Roman Minikayev ^a, Andrew Fitch ^b and Marek Berkowski ^a
aInstitute of Physics, Polish Academy of Sciences, Al.Lotnikow 32/46, Warsaw, Poland. E-mail: rahimi@ifpan.edu.pl
^bEuropean Synchrotron Radiation Facility, 71 avenue des Martyrs, Grenoble 38000, France

First published on 29th August 2024

---

---

1 Introduction

Vanadates, which are multi-component oxides containing vanadium, have attracted significant attention from scientists and technologists. These compounds represent an emerging field with a wide range of applications. Studies have highlighted their usefulness in various areas, including in medicine,¹ optoelectronics,^2,3 solar-energy-driven water oxidation,⁴ catalytic generation of molecular oxygen,⁵ catalytic water splitting,⁶ and for energy storage applications.⁷ Among these vanadates are those of whitlockite structure.

Whitlockite, named after Herbert Percy Whitlock (1868–1948), an American mineralogist, is a mineral of the idealized formula Ca₉(MgFe²⁺)(PO₄)₆PO₃OH. Synthetic and natural materials crystallizing in whitlockite-type structures form an extended family of compounds, including multiple phosphates, vanadates, and several arsenates. Such compounds crystallize in R3c space group with the unit cell size of a ≈ 10–11 Å, c ≈ 37–39 Å.

The addition of substituent at cationic sites within the parent compound, β-Ca₃(PO₄)₂ (β-TCP) or Ca₃(VO₄)₇ (TCV), is an effective tool to modify physicochemical properties of the material. Generally, transition metal ions can be incorporated into the lattice of luminescent materials in order to improve their optical behavior. For instance, cobalt doping enhances the emission and absorption efficiencies of various inorganic hosts, e.g., TiO₂ and perovskite.^8,9As some substituted or/and doped rare earth into TCV are known to be connected with attractive optoelectronic properties,^10–16 co-substitution of rare earth with transition metal enhance the luminescence properties.¹⁷ For the case of structurally related material, co-substitution of Mn²⁺ with rare earth into β-TCP improve the luminescence properties.^18,19

On the other hand, the catalytic behavior of Ca_3−xCo_x(PO₄)₂ and Ca_10.5−xCu_x(PO₄)₇ has been demonstrated.^20,21 For instance, the catalytic behavior of Ca_10.5−xCu_x(PO₄)₇ was studied in butan-2-ol conversion. The maximum activity in dehydrogenation was obtained by increasing the content of copper in such orthophosphate.

Only a limited number of studies have been reported on the substitution of divalent ions in TCV,^22–25 but interest in these materials is growing. In our previous work, we studied the effect of substituting nickel into TCV at ambient and high temperatures to determine the solubility limit and thermal expansion coefficient (TEC).²⁵ Additionally, two selected samples of Co and Cu were studied within a limited temperature range (300–800 K).²³ To extend our knowledge about the thermostructural properties of divalent ions substituted into TCV, whitlockite-type crystals, Ca_10.5−xTM_x(VO₄)₇ (TM = Co, Cu) (TM-TCV), are presented in this work based on room and high-temperature (300–1200 K) X-ray powder diffraction studies. The high-temperature investigation focuses on the impact of the transition metal content (x) on the thermal expansion behavior of these compounds.

2 Materials and methods

Polycrystalline samples with the formula Ca_10.5−xTM_x(VO₄)₇ (TM = Co, Cu), where x = 0–1 (sample names as S1–S6 refer to x = 0.16–1, whereas data for x = 0 are taken from our previous work³⁴), were synthesized by solid-state reaction. The samples were prepared using stoichiometric ratios of CaCO₃ (99.995%), CoO (99.7%) (or CuO (99.9%)), and V₂O₅ (99.995%). For each composition, the powders were mixed and formed into pellets at air atmosphere. Calcination of the pellets took place in three steps sequentially, each lasting 6 hours. The temperature was set at 1273 K for the first step and maintained at 1173 K for the subsequent two steps. The compound formation proceeded in accordance with the given reaction:

(10.5 − x)CaCO3 + 3.5V2O5 + xTMO → Ca10.5−xTMx(VO4)7 + Co2↑

Room temperature X-ray powder diffraction (XRPD) measurements were performed using a Philips XPert Pro Alpha1 diffractometer with CuKα₁ radiation. The experimental configuration followed Bragg–Brentano geometry and operated in continuous scanning mode. The diffractometer was equipped with a linear silicon strip detector, and in room temperature (RT) studies, a Ge(111) Johansson monochromator for the incident beam was employed. The use of such a detector was initially outlined in ref. 26, and details of the instruments settings can be found in the ref. 27. Powder X-ray diffraction data were collected at room temperature within the 6°–159.2° (2θ) range, employing a step size of 0.0167°. Crystal structures were refined using the Rietveld method^28,29 (Fullprof software version April 2019³⁰). High temperature diffraction measurements were carried out using the same diffractometer equipped with an HTK 1200 N (Anton Paar) temperature stage, in the Bragg–Brentano geometry. These X-ray powder diffraction data were collected at high temperatures over the range of 9°–100° (2θ) with CuKα radiation. The temperature range from room temperature (300 K) to 1200 K was selected, with different temperature steps (usually 50 or 100 K). A waiting time of 2 minutes was imposed after each temperature step to allow the heater to stabilize, ensuring a uniform temperature distribution within the sample. High temperature (HT) powder diffraction measurements were also performed by high-resolution X-ray powder diffraction at the ID22 beamline at the European Synchrotron Radiation Facility (ESRF) in the temperature range 300(1)–1200(1) K using a hot-air blower for two selected samples. The high-resolution diffraction data were collected at HT over the angular range of 2°–40° (2θ) using a wavelength of 0.400218(4) Å. XRD patterns were measured from a fine powder of Ca₁₀Co_0.5(VO₄)₇ and Ca₁₀Cu_0.5(VO₄)₇ sealed in a 0.7 mm diameter capillary. Air atmosphere was used for both high-temperature measurements.

3 Results and discussion

3.1 Study at room temperature as function of TM content

The phase analysis based on XRPD patterns confirms the formation of whitlockite type materials with R3c space group for all samples. However, in most Ca_10.5−xTM_x(VO₄)₇ samples, a trace of Ca₂V₂O₇ was noticed. In the case of Ca_9.67Co_0.83(VO₄)₇, a trace of cobalt garnet, Ca_2.5Co₂(VO₄)₃, was identified. Additionally, for the Ca_10.34Co_0.16(VO₄)₇, Ca_10.34Cu_0.16(VO₄)₇ and Ca_10.17Cu_0.33(VO₄)₇ samples, some foreign peaks were observed, but the corresponding phase was not identified. Despite additional annealing of these samples, the foreign phase remained. For all samples, Rietveld refinement was performed by employing the structure of Ca_2.71Mg_0.29(PO₄)₂³¹ as initial model. For peak shape determination, a pseudo-Voigt function was used. Two asymmetry parameters were considered. For more details see ref. 23. The refinement process yielded fractional replacement of Ca by TM. The refinement result of Ca_9.84Co_0.66(VO₄)₇ at room temperature (298(2) K) (Fig. 1) is a representative example for good matching between the observed diffraction pattern and calculated pattern after refinement and also the quality of refinement. In the case of Ca_10.5−xCo_x(VO₄)₇, Ca₂V₂O₇ phase increases slightly from x = 0.33, with its proportion rising from 1.4 wt% to 2.4 wt% for x = 1. Similarly, for Ca_10.5−xCu_x(VO₄)₇ samples, a secondary phase related to Ca₂V₂O₇ started to appear from x = 0.5. The proportion of this phase gradually increased from 3.3% at x = 0.5 to 6.2% at x = 1. The lattice parameters of the minor phase, Ca₂V₂O₇, closely matched those reported in ref. 32. Additionally, structural data for the garnet Ca_2.5Co₂(VO₄)₃, which appears in the samples with x = 0.83 and 1, are taken from ref. 33.

3.2 Study as function temperature for selected TM content

High-temperature measurements were carried out for selected samples, Ca_10.5−xCo_x(VO₄)₇ (x = 0.5, 0.66, 0.78), and Ca_10.5−xCu_x(VO₄)₇ (x = 0.5, 0.66, 0.75). For all these samples, diffraction patterns demonstrate that there is no phase transition in temperature range from room temperature (RT) up to 1200 K. With increasing temperature, the diffraction peaks shift slightly towards the low-angle side, due to a continuous lattice expansion. In some papers referring to structurally related compounds containing trivalent substituent in TCV, some anomalies in unit cell size at high temperature were reported which connect to phase transition and changes in symmetry (R3c to Rc) for Ca₉X(PO₄)₇ where X = In,⁵³ Fe,⁵⁴ Eu.⁵⁵ For crystals containing substituents such as Y and Bi, an additional phase transition possibility is a change in space group from Rc to Rm at higher temperature.^56,57 Notably, for the case of TM²⁺ substitution, no such transition has been reported. Attempts to use the space group Rm for Ca_10.5−xTM_x(VO₄)₇ XRD patterns obtained at high temperature have not been successful. As a result, the transition in symmetry from R3c to Rm can be excluded. Notably, the Rm structure does not account for several experimentally observed peaks, specifically those with odd Miller indices such as (223), (315), and (137), which are consistent with the structure described by the R3c space group.

Laboratory Rietveld refinements results give information about variation of the lattice parameters and volume with temperature. All compounds show a consistent expansion with temperature evolution for lattice parameters (a, c) and unit cell volume up to around 800 K. At higher temperatures, an anomaly is detected in the slope of the c lattice parameter's temperature dependence. The axial ratio (as shown in Fig. 4) provides a straightforward means to observe this week feature. The trend in the c/a(T) variation is such that decreases for all compounds from room temperature until approximately 800 K. Beyond this temperature, the slope of the c/a(T) changes, suggesting that the lattice parameter c increases more rapidly with temperature than the lattice parameter a.

In general, the non-linear behavior of lattice parameters in whitlockite type materials suggests some reordering in structure occurs with rising temperature. The inflection temperature (T_inf) marks the temperature at which these changes in lattice parameters occur. T_inf decreases by increasing content of transition metals. For instance, Ca₁₀Co_0.5(VO₄)₇ exhibits T_inf at 871(13) K, whereas for Ca_9.72Co_0.78(VO₄)₇, T_inf occurs at 813(10) K. For Ca_10.5−xCu_x(VO₄)₇, this reduction is from 809(8) to 770(9) as x increases from 0.5 to 0.75.

For many materials, including minerals of various structural complexities, an approximation of unit cell size variation with temperature (at high temperature) is successfully achieved using the Laurent polynomial (see, e.g., the review by Fei⁵⁸). If anomalies in lattice parameters behavior are observed, then a different description of the variation is required. For the TM-TCV, we apply a combined approach: (I) the behavior below the anomaly is described by the Laurent polynomial, whereas (II) the evaluation of the thermal expansion coefficient (TEC) is based on the Lagrangian interpolation method which is used for the entire range. In the temperature range from RT to 800 K, the temperature dependence of the lattice parameters and volume is well described by the equation L(T) = A + BT + C/T. The same equation has been used for related materials in similar temperature range.^23,25,59 Variations of thermal expansion coefficient with temperature for each variable, y, were calculated using equation

	(1)

The majority of TEC values calculated using Lagrangian interpolation are encompassed by the lines depicted through the Laurent polynomial model (Fig. 5). The values of linear and volumetric thermal expansion coefficients from room temperature up to approximately 800–900 K do not change significantly for all studied samples. The value of TEC along the a direction is slightly larger than along the c direction. However, above the T_inf, TEC in the c direction increase faster than in the a direction for cobalt containing samples. In general terms, the anisotropic behavior of TEC above T_inf increases more significantly with temperature for TM = Ni and Co-substitution than for Cu substitution. For both series of compounds, the volumetric thermal expansion shows larger values at the highest concentration of substitution. Cu-TCV has the largest volumetric TEC value (85 MK⁻¹) compared to Co (78 MK⁻¹) and Ni (60 MK⁻¹)²⁵ substituted samples.

For Ca₉Gd(VO₄)₇, the volumetric thermal expansion is 39 MK⁻¹ at room temperature and increases to 45 MK⁻¹ in the range from 600–1100 K.⁵⁹ One can notice that in the temperature range up to the inflection temperature, the value of volumetric thermal expansion for Ca_10.5−xTM_x(VO₄)₇ is relatively similar to Ca₉Gd(VO₄)₇. The effect of substituting ions appears in the change in the nature of anisotropy and the increase in thermal expansion at temperatures above T_inf.

4 Conclusions

This study provides the description of the Ca_10.5−xTM_x(VO₄)₇ crystal structure at room and high temperatures. Rietveld refinement of the structure from X-ray powder diffraction data defines the solubility limit which is 0.78(3) for TM = Co and 0.75(4) for TM = Cu. All samples below this limit crystallize in trigonal whitlockite-type structure type with the R3c space group. Analysis of the site occupancies at the available octahedral sites (M1–M5) shows a preference of TM²⁺ ions to enter the M5 site, in line with earlier reported results on the related materials of this kind, containing other small divalent ions substituting the Ca ions. Moreover, the variation of lattice parameters and thermal expansion coefficient as function of temperature was studied in range RT-1200 K for samples. Increasing temperature is found to cation rearrangement, potentially causing the observed anomalies in axial ratio and thermal expansion. The observed behavior of the axial ratio and thermal expansion coefficient as function of temperature is expected for other crystals containing small divalent substitution such as Mg and Zn (as has already been observed for the case of Ni). The structural model was analyzed to determine the occupancy of cationic sites by TM = Co, Cu at high temperature. In particular, According to the final result of structure model refinement, the M4 and M5 site are preferable sites for Cu ions above inflection temperature.

Data availability

The data presented in this study are available on request from the corresponding author.

Conflicts of interest

There are no conflicts to declare.

Appendix

Structural data of room and high temperature (see Tables 2, 3, 4, 5, 6 and 7).

---

---

---

---

---

---

Acknowledgements

The high-resolution powder diffraction at high-temperature experiments were performed on beamline ID22 at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. The access to ESRF was financed by the Polish Ministry of Education and Science decision number 2021/WK/11.

References

1. D. Rehder, Future Med. Chem., 2012, 4, 1823–1837 CrossRef CAS PubMed .
2. H. Yu, J. Liu, H. Zhang, A. A. Kaminskii, Z. Wang and J. Wang, Laser Photonics Rev., 2014, 8, 847–864 CrossRef CAS .
3. Y. Matsushima, T. Koide, M. Hiro-Oka, M. Shida, A. Sato, S. Sugiyama and M. Ito, J. Am. Ceram. Soc., 2015, 98, 1236–1244 CrossRef CAS .
4. Z.-F. Huang, L. Pan, J.-J. Zou, X. Zhang and L. Wang, Nanoscale, 2014, 6, 14044–14063 RSC .
5. J. M. Gonçalves, M. I. da Silva, L. Angnes and K. Araki, J. Mater. Chem. A, 2020, 8, 2171–2206 RSC .
6. L. Wang, X. Shi, Y. Jia, H. Cheng, L. Wang and Q. Wang, Chin. Chem. Lett., 2021, 32, 1869–1878 CrossRef CAS .
7. S. Pavithra, K. Pramoda and R. S. Keri, Chem. Eng. J., 2024, 153423 CrossRef CAS .
8. P. Jiang, W. Xiang, J. Kuang, W. Liu and W. Cao, Solid State Sci., 2015, 46, 27–32 CrossRef CAS .
9. Z. Cao, J. Li, L. Wang, K. Xing, X. Yuan, J. Zhao, X. Gao and H. Li, Mater. Res. Bull., 2020, 121, 110608 CrossRef CAS .
10. L. Andrade, D. R. Ardila, J. P. Andreeta and M. S. Li, Opt. Mater., 2003, 22, 369–375 CrossRef CAS .
11. L. Li, G. Wang, Y. Huang, L. Zhang, Z. Lin and G. Wang, J. Cryst. Growth, 2011, 314, 331–335 CrossRef CAS .
12. P. Hu and G. Wang, Mater. Res. Innovations, 2011, 15, 75–77 CrossRef CAS .
13. J. Zhao, C. Guo, J. Yu and R. Yu, Opt. Laser Technol., 2013, 45, 62–68 CrossRef CAS .
14. N. Zhuang, X. Liu, Q. Xu, X. Chen, B. Zhao, X. Hu and J. Chen, J. Alloys Compd., 2014, 595, 113–119 CrossRef CAS .
15. L. Ivleva, E. Dunaeva, I. Voronina, M. Doroshenko and A. Papashvili, J. Cryst. Growth, 2018, 501, 18–21 CrossRef CAS .
16. L. Ivleva, E. Dunaeva, I. Voronina, M. Doroshenko, A. Papashvili, J. Sulc, J. Kratochvíl and H. Jelinkova, J. Cryst. Growth, 2019, 513, 10–14 CrossRef CAS .
17. M. Dai, K. Qiu, W. Zhang and Q. Tang, J. Mater. Sci.: Mater. Electron., 2018, 29, 15052–15059 CrossRef CAS .
18. N. Guo, Y. Huang, H. You, M. Yang, Y. Song, K. Liu and Y. Zheng, Inorg. Chem., 2010, 49, 10907–10913 CrossRef CAS PubMed .
19. C.-H. Huang, T.-W. Kuo and T.-M. Chen, ACS Appl. Mater. Interfaces, 2010, 2, 1395–1399 CrossRef CAS PubMed .
20. A. Benarafa, M. Kacimi, G. Coudurier and M. Ziyad, Appl. Catal., A, 2000, 196, 25–35 CrossRef CAS .
21. A. Legrouri, S. Romdhane, J. Lenzi, M. Lenzi and G. Bonel, J. Mater. Sci., 1996, 31, 2469–2473 CrossRef CAS .
22. I. Voronina, V. Voronov, E. Dunaeva, L. Iskhakova, A. Papashvili, M. Doroshenko and L. Ivleva, J. Cryst. Growth, 2021, 555, 125965 CrossRef CAS .
23. H. S. Rahimi Mosafer, W. Paszkowicz, R. Minikayev, M. Kozłowski, R. Diduszko and M. Berkowski, Dalton Trans., 2021, 50, 14762–14773 RSC .
24. G. M. Kuz'micheva, L. I. Ivleva, I. A. Kaurova, V. A. Lazarenko and E. V. Khramov, J. Solid State Chem., 2023, 318, 123776 CrossRef .
25. H. S. Rahimi Mosafer, W. Paszkowicz, R. Minikayev, C. Martin, M. Kozłowski, O. Chukova, Y. Zhydachevskyy and S. Nedilko, Crystals, 2023, 13, 853 CrossRef .
26. A. Zięba, W. Dąbrowski and A. Czermak, The First Polish Meeting on High-Resolution X-ray Diffraction and Topography, Szklarska Poręba, 1996, pp. 14–17.
27. W. Paszkowicz, Nucl. Instrum. Methods Phys. Res., Sect. A, 2005, 551, 162–177 CrossRef CAS .
28. B. Loopstra and H. Rietveld, Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem., 1969, 25, 787–791 CrossRef CAS .
29. H. M. Rietveld, J. Appl. Crystallogr., 1969, 2, 65–71 CrossRef CAS .
30. J. Rodriguez-Carvajal, Satellite meeting on powder diffraction of the XV congress of the IUCr, 1990.
31. L. Schroeder, B. Dickens and W. Brown, J. Solid State Chem., 1977, 22, 253–262 CrossRef CAS .
32. Y.-P. Tong, G.-T. Luo, Z. Jin and Y.-W. Lin, Aust. J. Chem., 2011, 64, 973–977 CrossRef CAS .
33. K. M. Kosyl, W. Paszkowicz, R. Minikayev, M. Berkowski, M. Czech, A. Reszka and L. Kilanski, J. Alloys Compd., 2019, 779, 863–869 CrossRef CAS .
34. R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr., 1976, 32, 751–767 CrossRef .
35. R. Enderle, F. Götz-Neunhoeffer, M. Göbbels, F. Müller and P. Greil, Biomaterials, 2005, 26, 3379–3384 CrossRef CAS PubMed .
36. S. Kannan, F. Goetz-Neunhoeffer, J. Neubauer and J. M. Ferreira, J. Am. Ceram. Soc., 2009, 92, 1592–1595 CrossRef CAS .
37. K. Spaeth, F. Goetz-Neunhoeffer and K. Hurle, J. Solid State Chem., 2020, 285, 121225 CrossRef CAS .
38. D. V. Deyneko, D. A. Petrova, S. M. Aksenov, S. Y. Stefanovich, O. V. Baryshnikova, S. S. Fedotov, P. C. Burns, M. B. Kosmyna, A. N. Shekhovtsov and B. I. Lazoryak, CrystEngComm, 2019, 21, 1309–1319 RSC .
39. J. Sánchez-Martín, D. Errandonea, H. S. Rahimi Mosafer, W. Paszkowicz, R. Minikayev, R. Turnbull, M. Berkowski, J. Ibáñez-Insa, C. Popescu and A. Fitch, et al. , CrystEngComm, 2023, 25, 1240–1251 RSC .
40. A. Legrouri, J. Lenzi and M. Lenzi, J. Therm. Anal. Calorim., 1994, 41, 1041–1052 CrossRef CAS .
41. K. Yoshida, H. Hyuga, N. Kondo, H. Kita, M. Sasaki, M. Mitamura, K. Hashimoto and Y. Toda, J. Am. Ceram. Soc., 2006, 89, 688–690 CrossRef CAS .
42. Z. Leng, R. Li, L. Li, D. Xue, D. Zhang, G. Li, X. Chen and Y. Zhang, ACS Appl. Mater. Interfaces, 2018, 10, 33322–33334 CrossRef CAS PubMed .
43. N. G. Dorbakov, V. V. Grebenev, V. V. Titkov, E. S. Zhukovskaya, S. Y. Stefanovich, O. V. Baryshnikova, D. V. Deyneko, V. A. Morozov, A. A. Belik and B. I. Lazoryak, J. Am. Ceram. Soc., 2018, 101, 4011–4022 CrossRef CAS .
44. N. G. Dorbakov, V. V. Titkov, S. Y. Stefanovich, O. V. Baryshnikova, V. A. Morozov, A. A. Belik and B. I. Lazoryak, J. Alloys Compd., 2019, 793, 56–64 CrossRef CAS .
45. A. Altomare, R. Rizzi, M. Rossi, A. El Khouri, M. Elaatmani, V. Paterlini, G. Della Ventura and F. Capitelli, Crystals, 2019, 9, 288 CrossRef CAS .
46. J. Fan, W. Zhou, J. Luo, J. Zhang, Z.-c. Wu, X. Dai and X. Zhang, Ceram. Int., 2022, 48, 15695–15702 CrossRef CAS .
47. A. Belik, V. Morozov, S. Khasanov and B. Lazoryak, Mater. Res. Bull., 1998, 33, 987–995 CrossRef CAS .
48. N. Khan, V. Morozov, B. Lazoryak and S. Khasanov, Mater. Res. Bull., 1997, 32, 1211–1220 CrossRef CAS .
49. T. Debroise, E. Colombo, G. Belletti, J. Vekeman, Y. Su, R. Papoular, N. S. Hwang, D. Bazin, M. Daudon and P. Quaino, et al. , Cryst. Growth Des., 2020, 20, 2553–2561 CrossRef CAS .
50. K. Matsunaga, T. Kubota, K. Toyoura and A. Nakamura, Acta Biomater., 2015, 23, 329–337 CrossRef CAS PubMed .
51. I. Mayer, S. Cohen, S. Gdalya, O. Burghaus and D. Reinen, Mater. Res. Bull., 2008, 43, 447–452 CrossRef CAS .
52. A. Altomare, N. Corriero, C. Cuocci, A. Falcicchio, A. Moliterni and R. Rizzi, J. Appl. Crystallogr., 2018, 51, 1229–1236 CrossRef CAS .
53. V. Morozov, A. Belik, S. Y. Stefanovich, V. Grebenev, O. Lebedev, G. Van Tendeloo and B. Lazoryak, J. Solid State Chem., 2002, 165, 278–288 CrossRef CAS .
54. B. I. Lazoryak, V. A. Morozov, A. A. Belik, S. Y. Stefanovich, V. V. Grebenev, I. A. Leonidov, E. B. Mitberg, S. A. Davydov, O. I. Lebedev and G. Van Tendeloo, Solid State Sci., 2004, 6, 185–195 CrossRef CAS .
55. R. A. Benhamou, A. Bessiere, G. Wallez, B. Viana, M. Elaatmani, M. Daoud and A. Zegzouti, J. Solid State Chem., 2009, 182, 2319–2325 CrossRef CAS .
56. B. I. Lazoryak, S. M. Aksenov, S. Y. Stefanovich, N. G. Dorbakov, D. A. Belov, O. V. Baryshnikova, V. A. Morozov, M. S. Manylov and Z. Lin, J. Mater. Chem. C, 2017, 5, 2301–2310 RSC .
57. A. A. Belik, V. A. Morozov, D. V. Deyneko, A. E. Savon, O. V. Baryshnikova, E. S. Zhukovskaya, N. G. Dorbakov, Y. Katsuya, M. Tanaka and S. Y. Stefanovich, et al. , J. Alloys Compd., 2017, 699, 928–937 CrossRef CAS .
58. Y. Fei and T. Ahrens, Mineral physics and crystallography: a handbook of physical constants, 1995, vol. 2, pp. 29–44 Search PubMed .
59. W. Paszkowicz, A. Shekhovtsov, M. Kosmyna, P. Loiko, E. Vilejshikova, R. Minikayev, P. Romanowski, W. Wierzchowski, K. Wieteska and C. Paulmann, et al. , Nucl. Instrum. Methods Phys. Res., Sect. B, 2017, 411, 100–111 CrossRef CAS .
60. R. Gopal and C. Calvo, Z. Kristallogr. – Cryst. Mater., 1973, 137, 67–85 CrossRef CAS .
61. K. M. Kosyl, W. Paszkowicz, A. N. Shekhovtsov, M. B. Kosmyna, J. Antonowicz, A. Olczak and A. N. Fitch, Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater., 2020, 76, 554–562 CrossRef CAS PubMed .

This journal is © The Royal Society of Chemistry 2024