MIREA – Russian Technological University, Moscow, Russia:

A. M. Veselov, Master’s Student
G. V. Zimina, Lead Researcher of the Bolshakov Department of Chemistry and Technology of Rare and Dispersed Elements, Nanoscale and Composite Materials
V. V. Fomichev, Professor of the Bolshakov Department of Chemistry and Technology of Rare and Dispersed Elements, Nanoscale and Composite Materials, e-mail: valeryfom@rambler.ru

Lomonosov Moscow State University, Moscow, Russia:

F. M. Spiridonov, Associate Professor of the Inorganic Chemistry Department

Solid-phase synthesis and X-ray analysis methods were used to study a phase formation in BaNb₂O₆ – SrNb₂O₆ quasi-binary system within a temperature range of 950–1200 ^oC. Strontium and barium carbonates and niobium oxide were used as initial substances. It was found that the components of the system started to interact at 950 ^oC already. At such temperature the system contains two single-phase zones: tetragonal solid solutions based on barium niobate with strontium niobate up to 10% (mol.) and a monoclinic form based on strontium niobate with a content of over 85% (mol.), and a double-phase zone with the strontium niobate content within a range of 10–85% (mol.) — a mixture of these solid solutions. At 1100 ^oC the system contains three zones of tetragonal solid solutions: based on barium niobate Sr_xBa_{1 – x}Nb₂O₆ (х ≤ 0.05); based on strontium niobate (х ≥ 0.85); based on complex niobate Sr_xBa_{1 – x}Nb₂O₆ (0.3 ≤ x ≤ 0.4), showing ferro electric behavior. At 1100 ^oC there are zones of solid solution mixtures: at 0.05 ≤ x ≤ 0.3 — barium niobate-based and complex-niobate tetragonal solid solutions, and at 0.4 ≤ x ≤ 0.85 — a mixture of two solid solution forms based on complex niobate: high-temperature tetragonal and low-temperature monoclinic forms with a strontium niobatebased solid solution. An increase in synthesis temperature to 1200 ^oC results in a sudden expansion (0.2 ≤ x ≤ 0.75) of a zone of the tetragonal solid solution based on complex niobate Sr_xBa_{1 – x}Nb₂O₆, showing ferroelectric behavior, and elimination of a monoclinic form of such solution mixed with the strontium niobate-based solution. Thus, the research performed showed that it was feasible to decrease synthesis temperature of Sr_xBa_{1 – x}Nb₂O₆ tetragonal solid solution (ferroelectric material) from 1400 to 1200 ^oC.

1. Smolensky G. A. Physics of ferroelectric phenomena: textbook. Leningrad : Nauka, 1985. 396 p.
2. Korovin S. S., Zimina G. V., Reznik A. M., Bukin V. I. Rare and dispersed elements. Chemistry and technology. Moscow : MISiS, 1996. Vol. 1. 376 p.
3. Ulex M., Pankrath R., Betzler K. Growth of strontium barium niobate: the liquidus–solidus phase diagram. Journal of crystal growth. 2004. Vol. 271, No. 1-2. pp. 128–133.
4. Dong-Wan Kim, Hee Bum Hong, Kug Sun Hong, Chang Kyung Kim, Deug Joong Kim. The reversible phase transition and dielectric properties of BaNb₂O₆ polymorphs. Japanese journal of applied physics. 2002. Vol. 41, No. 10. pp. 6045–6048.
5. Bonner W. A., Carruthers J. R., O'Bryan H. M. Jr. Effects of changes in melt composition on crystal growth of barium sodium niobate. Materials research bulletin. 1970. Vol. 5, No. 4. pp. 243–252.
6. Simonov V. I. An atomic structure and physical properties of crystals. Kristallografiya. 2003. Vol. 48, No. 6. pp. 91–102.
7. Leitner J., Hampl M., Ruzicka K., Straka M., Sedmidubský D., Svoboda P. Thermodynamic properties of strontium metaniobate SrNb₂O₆. Journal of thermal analysis and calometry. 2008. Vol. 91, No. 3. pp. 985–998.
8. Zibrov I. P., Filonenko V. P., Werner P.-E., Marinder B.-O., Sundberg M. A new high-pressure modification of Nb₂O₅. Journal of solid state chemistry. 1998. Vol. 141, Iss. 1. pp. 205–211.
9. Smirnova K. A., Fomichev V. V., Drobot D. V., Nikishina E. E. Obtaining nanosized niobium and tantalum pentoxides by using supercritical antisolvent fluid technology. Fine chemical technologies. 2015. Vol. 10, No. 1. pp. 76–82.
10. Tarasova N., Colomban Ph., Animitsa I. The short-range structure and hydration process of fluorine-substituted double perovskites based on bariumcalcium niobate Ba₂CaNbO_5.5. Journal of physics and chemistry of solids. 2018. Vol. 118. pp. 32–39.
11. Maalti Puri, Sukhteen Bindra Narang, Shalini Bahel. Influence of frequency and temperature on dielectric and electrical properties of Ca-substituted barium iron niobate. Ceramics international. 2018. Vol. 44. pp. 9112–9124.
12. Chernaya T. S., Maksimov B. A., Volk T. R., Ivleva L. I., Simonov V. P. An atomic structure of Sr_0.75Ba_0.25Nb₂O₆ monocrystal and relations between a composition, a structure and properties in (Sr,Ba)Nb₂O₆ solid solutions. Fizika tverdogo tela. 2000. Vol. 42, No. 9. pp. 1668–1672.
13. Desplanches G., Barraud Y., Lazennec Y. A new crystalline form in the BaNb₂O₆ – SrNb₂O₆ pseudo-binary system. Journal of crystal growth. 1974. Vol. 23. pp. 149–150.
14. Yun Rao, Hanxing Liu, Hua Hao, Zhonghua Yao et al. MgO-modified Sr_0.7Ba_0.3Nb₂O₆ ceramics for energy storage applications. Ceramic international. 2018. Vol. 44, No. 10. pp. 11022–11029.
15. Boniort Y. Y., Brehm C., Desplanches G., Barraud J.-Y., Margotin P. Crystal growth of strontium barium niobate Ba_xSr_{1 – x}Nb₂O₆. Journal of crystal growth. 1975. Vol. 30, No. 3. pp. 357–362.
16. Ottini R., Tealdi C., Tomasi C. et al. Local environments and transport properties of heavily doped strontium barium niobates Sr_0.5Ba_0.5Nb₂O₆. Journal of solid state chemistry. 2018. Vol. 258. pp. 99–107.