Effect of Ba-incorporation on pressure-induced structural changes in the relaxor ferroelectric $PbSc_{0.5}Ta_{0.5}O_{3}$

Pressure-induced structural changes in the canonical relaxor Pb0.78Ba0.22Sc0.5Ta0.5O3were studied with bothin-house and synchrotron single-crystal x-ray diffraction as well as Raman spectroscopy at pressures up to 9.8GPa. The results reveal that the substitution of Ba for Pb inABO3perovskite-type structures, i.e., the substi-tution of a two-valent element with an isotropic electron shell for an isovalent element with a stereochemicallyactive lone pair, leads to a “diffuse pressure-induced phase transition,” a structural transformation over a broadpressure range, without a well-defined critical pressure point. The smeared phase transition of the averagestructure results from the existence of local structural deformations in the vicinity of A-positioned Ba cation