Composition-, Temperature- and Pressure-Induced Transitions between High-Pressure Stabilized Perovskite Phases of the (1-x)BiFe0.5Sc0.5O3 - xLaFe0.5Sc0.5O3 Series

Abstract

Crystal structures of the high-pressure synthesized perovskite phases of the (1-x)BiFe0.5Sc0.5O3-xLaFe0.5Sc0.5O3 (0¼ x - 1) system and their temperature and pressure behaviours were studied using laboratory and synchrotron Xray diffractions as well as neutron diffraction. At room temperature, the as-prepared phases with x < 0.05 have an antipolar structure with the Pnma symmetry and with the √2ap x 4ap x2√2ap superstructure (where ap is the pseudocubic perovskite unit-cell parameter). An incommensurately modulated phase with the Imma(00γ)s00 superspace group is observed for 0.10 ¼ x < 0.33, while a non-polar Pnma phase (√2apx 2ap x √2ap) is stable when x > 0.34. The antipolar Pnma phase in the as-prepared samples with composition corresponding to x ¼ 0 transforms into the polar Ima2 one via irreversible annealing-caused transformation accompanied by a formation of a high-temperature intermediate polar R3c polymorph, while the antipolar Pnma phase in samples with x ¼ 0.05 is stable until the decomposition temperature. In the solid solutions with 0.10 ¼ x < 0.33, increasing temperature was found to result in a reversible transformation of the Imma(00γ)s00 phase into a non-polar Pnma one. The transition temperature decreases with increasing x. A hydrostatic pressure of few GPa was also shown to induce a reversible Imma(00γ)s00 → Pnma transformation.