Effect of postgrowth annealing in an oxygen-containing atmosphere on the microhardness of single-crystal calcium molybdate CaMoO4

Monocrystalline calcium molybdenum CaMoO₄ is a well-known material. Recently, there has been a surge of interest in CaMoO₄ due to a number of popular applications, such as working medium for a cryogenic scintillation bolometer. During growth CaMoO₄ single crystals acquire a blue color due to the presence of defective centers, such as color centers, which is unacceptable for optical applications. To eliminate the coloration, annealing in an oxygen-containing atmosphere is used and then the necessary elements are prepared from the crystals by mechanical influences (cutting, polishing, etc.). In this regard, for the rational solution of issues arising in the manufacture of products from these crystals and their further practical use, the assessment of the mechanical properties of these crystalline materials is an urgent task. However, the results of studies of the mechanical properties of CaMoO₄ are poorly presented, without taking into account anisotropy; there is a significant spread of data on the value of hardness by Mohs. For different authors, hardness varies from 3.5 to 6. In this paper, samples of single crystals of calcium molybdate in the initial state and after high-temperature annealing of different duration in an oxygen-containing atmosphere are studied. It is shown that prolonged annealing leads to discoloration of crystals. It has been established that calcium molybdate crystals are extremely brittle, the brittleness score of Zp crystals in the initial state is maximum and is 5, annealing leads to a decrease in the brittleness score to 4. The “viscosity” parameters are calculated by the Palmqvist S method. The nubs of complete destruction of F_pr prints were established, it was shown that annealing in an oxygen-containing atmosphere leads to an increase in F_pr by 2.5 times for the Z-cut, by 10 times for the X-cut. It is shown that the microhardness of crystals is characterized by anisotropy of the II kind: for all samples, the microhardness of the Z-cut is higher than the microhardness of the X-cut. The anisotropy coefficients of the microhardness of the KH samples are estimated. On the basis of the measured values of microhardness, the degrees of ionic bonds I are calculated.

1. Botden Th.P.J., Kröger F.A. Energy transfer in tungstates and molybdates activated with samarium. Physica. 1949; 15(8-9): 747—768. https://doi.org/10.1016/0031-8914(49)90080-4

2. Blistanov A.A. Crystals of quantum and nonlinear optics. Moscow: MISiS; 2000. 432 p. (In Russ.)

3. Limarenko L.N., Nosenko A.E., Pashkovskii M.V., Futorskii D.-L.L. Effect of structural defects on the physical properties of tungstates. M.V. Pashkovskii (ed.). Lviv: Vishcha shkola; 1978. 160 p. (In Russ.)

4. Basiev T.T., Sobol A.A., Voronko Yu.K., Zverev P.G. Spontaneous Raman spectroscopy of tungstate and molybdate crystals for Raman lasers. Optical Materials. 2000; 15(3): 205—216. https://doi.org/10.1016/S0925-3467(00)00037-9

5. Handbook of Mineralogy. URL: http://www.handbookofmineralogy.org/ (accessed on 12.02.2023).

6. Gurmen E., Daniel E., King J.S. Crystal structure refinement of SrMoO4, SrWO4, CaMoO4, and BaWO4 by neutron diffraction. Journal of Chemical Physics. 1971; 55(3): 1093—1097. https://doi.org/10.1063/1.1676191

7. Harris S.E., Nieh S.T.K., Feigelson R.S. CaMoO4 electronically tunable optical filter. Applied Physics Letters. 1970; 17(5): 223—225. https://doi.org/10.1063/1.1653374

8. Parygin V.N., Vershubskiǐ A.V., Kholostov K.A. Control of the characteristics of a calcium molybdate collinear acousto-optic filter. Technical Physics. 1999; 44(12): 1467—1471.

9. ТBasiev T.T., Osiko V.V. New materials for SRS lasers. Russian Chemical Reviews. 2006; 75(10): 847—862.

10. Khanbekov N.D. AMoRE: Collaboration for searches for the neutrinoless double-beta decay of the isotope of 100Mo with the AID of 40Ca100MoO4 as a cryogenic scintillation detector. Physics of Atomic Nuclei. 2013; 76(9): 1086—1089.https://doi.org/10.7868/S0044002713090109

11. Korzhik M.V., Kornoukhov V.N., Missevitch O.V., Fedorov A.A., Annenkov A.N., Buzanov O.A., Borisevicth A.E., Dormenev V.I., Kholmetskii A.L., Kim S.K. Kim Y., Kim H., Bratyakina A.V. Large volume CaMoO4 scintillation crystals. IEEE Transactions on nuclear Science. 2008; 55(3): 1473—1475. https://doi.org/10.1109/TNS.2008.920428

12. Annenkov A.N., Buzanov O.A., Danevich F.A., Georgadze A.Sh., Kim S.K., Kim H.J., Kim Y.D., Kobychev V.V., Kornoukhov V.N., Korzhik M., Lee J.I., Missevitch O., Mokina V.M., Nagorny S.S., Nikolaiko A.S., Poda D.V., Podviyanuk R.B., Sedlak D.J., Shkulkova O.G., So J.H., Solsky I.M., Tretyak V.I., Yurchenko S.S. Development of CaMoO4 crystal scintillators for a double beta decay experiment with 100Mo. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 2008; 584(2-3): 334345. https://doi.org/10.1016/j.nima.2007.10.038

13. Pan S., Zhang J., Pan J., Ren G., Lee J, Kim H. Thermal expansion, luminescence, and scintillation properties of CaMoO4 crystals grown by the vertical Bridgman method. Journal of Crystal Growth. 2018; 734: 179—187. https://doi.org/10.1016/j.jcrysgro.2018.05.033

14. Jiang L., Wang Zh., Chen H., Chen Y., Chen P., Xu Z. Thermal annealing effects on the luminescence and scintillation properties of CaMoO4 single crystal grown by Bridgman method. Journal of Alloys and Compounds. 2018; 734: 179—187. https://doi.org/10.1016/j.jallcom.2017.11.005

15. Flournoy P.A., Brixner L.H. Laser characteristics of niobium compensated CaMoO4 and SrMoO4. Journal of the Electrochemical Society. 1965; 112(8): 779—781. https://doi.org/10.1149/1.2423694

16. Boyarskaya Yu.S. Deformation of crystals during microhardness tests. Kishinev: Shtiintsa; 1972. 235 p. (In Russ.)

17. Lebedeva S.I. Determination of the microhardness of minerals. Moscow: Izd-vo Akademii nauk SSSR; 1963. 123 p. (In Russ.)

18. Shaskol’skaya M.P. Crystallography. Moscow: Vysshaya shkola; 1984. 375 p. (In Russ.)

19. GOST Р 8.748-2011 (ICO 14577-1:2002). State system for ensuring the uniformity of measurements. Metallic materials. Instrumented indentation test for hardness and materials parameters. Part 1. Test method. 01.05.2013. (In Russ.)

20. Mohs scale. Centipedes. Bluegrass. Great Soviet Encyclopedia. In 50 vol. Moscow: Sovetskaya entsiklopediya; 1949—1958. Vol. 28. P. 268. (In Russ.)

21. Didenko I.S., Kozlova N.S., Kugaenko O.M., Petrakov V.S. Physics of a real crystal. Moscow: Izdatel’skii Dom NITU “MISiS”; 2013. 75 p. (In Russ.)

22. Betekhtin A.G. Mineralogy. Moscow: Gosgeolizdat; 1950. 956 p. (In Russ.)

23. Batra N. M., Arora S. K., Mathews T. Study of crack patterns during indentation on CaMoO4 single crystals. Journal of Materials Science. 1988; 7(3): 254—256. https://doi.org/10.1007/BF01730188

24. Weber M.J. Handbook of optical materials. Boca Raton: CRC Press; 2003. 536 p.

25. GOST 2999-75. Metals and alloys. Vickers hardness test by diamond pyramid. 01.07.1976. (In Russ.)

26. GOST 9450-76 (CT CMEA 1195-78). Measurements microhardness by diamond instruments indentation. 01.01.1977. (In Russ.)

27. GOST Р ИСО 6507-1-2007. Metals and alloys. Vickers hardness test. Part 1. Test method. 01.08.2008. (In Russ.)

28. Glazov V.M., Vigdorovich V.N. Microhardness of metals. Moscow: Metallurgizdat; 1962. 224 p. (In Russ.)

29. Pillay K.S. Relationship between hardness and ionicity in a crystal. Indian Journal of Pure & Applied Physics. 1982; 20: 46—48.

30. Raghuram D.V., Raghavendra Rao A., Prasad P.M., Madhu G., Manikumari V.A Correlation between hardness and bond ionicity in crystals. International Journal for Research in Applied Science & Engineering Technology. 2019; 7(3): 2680—2683. https://doi.org/10.22214/ijraset.2019.3488