Composition-, temperature- and pressure-induced transitions between high-pressure stabilized perovskite phases of the (1-x)BiFe0.5Sc0.5O3-xLaFe0.5Sc0.5O3 series

Crystal structures of the high-pressure synthesized perovskite phases of the (1-x)BiFe0.5Sc0.5O3-xLaFe0.5Sc0.5O3 (0 = x <= 1) system and their temperature and pressure behaviours were studied using laboratory and synchrotron X-ray 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 V2ap x 4ap x 2V2ap superstructure (where ap is the pseudocubic perovskite unit-cell parameter). An incommensurately modulated phase with the Imma(00 gamma)s00 superspace group is observed for 0.10 = x <= 0.33, while a non-polar Pnma phase (V2ap x 2ap x V2ap) is stable when x >= 0.34. The antipolar Pnma phase in the as-prepared samples with composition corresponding to x = 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 = 0.05 is stable until the decomposition temperature. In the solid solutions with 0.10 = x <= 0.33, increasing temperature was found to result in a reversible transformation of the Imma(00 gamma)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(00 gamma)s00 -> Pnma transformation.