Thermal expansion, T−x phase diagram and polarization of (1-x)Na1/2Bi1/2TiO3-xBaTiO3 solid solutions

Gorev, M.V., Flerov, I.N., Molokeev, M.S., (...), Sapozhnikov, S.V., Mikhaleva, E.A.// Journal of the European Ceramic Society//

https://doi.org/10.1016/j.jeurceramsoc.2024.116769

The paper presents the results of detailed studies of thermal expansion of solid solutions (1-x)Na $_{1 / 2}$ Bi $_{1 / 2}$ TiO $_{3}$ -xBaTiO $_{3}$ with x=0.04-0.97 in the temperature range from 100 to 900 K. A change in chemical pressure associated with the complex cationic substitution, (Na $_{1 / 2}$ Bi $_{1 / 2}$ ) $^{2 +} \to$ Ba $^{2 +}$ , result in a very rapid decrease in the temperatures of the transformation $P 4 m m \to C 2 m m \to R 3 m$ below 100 K which are characteristic of BaTiO $_{3}$ . Significant features in the behavior of thermal expansion were observed near two triple points in the $T - x$ phase diagram where the phases $P m \bar{3} m$ , $P 4 m m$ , $P 4 b m$ (x $\approx$ 0.15-0.20) and $P 4 b m$ , $P 4 m m$ , $R 3 c$ (x $\approx$ 0,06) coexist, allow the studied solid solutions to be divided into three groups. The relationship between the effects of internal chemical pressure and external hydrostatic one is discussed. By analyzing the thermodynamic potential, the root-mean-square polarization $P_{d}$ is determined, which increases by about 16% with a decrease in the BT content from 0.97 to 0.4.