New PbTiO3-Type Giant Tetragonal Compound Bi2ZnVO6 and Its Stability under Pressure

A new PbTiO3-type compound, Bi2ZnVO6, with a giant tetragonal distortion of c/a = 1.26 (a = 3.7869(3) angstrom, c = 4.7660(7) angstrom) was synthesized under high pressure high temperature conditions (9 GPa and 1373 K). A point charge model calculation based on the atomic positions refined by Rietveld analysis of synchrotron X-ray diffraction (SXRD) data gave an electrical ionic polarization of 126 mu C/cm(2), the largest value among PbTiO3-type perovskite compounds. The tetragonality (c/a) decreased with increasing temperature from 100 to 570 K without any trace of a phase transition. Instead, a pressure-induced transition from a polar tetragonal structure to a paraelectric GdFeO3 one accompanied by a 2.4% volume collapse was observed at 6.01 GPa. Bi2ZnVO6 showed paramagnetic behavior with S = 1/2 because of the random distribution of nonmagnetic Zn2+ and magnetic V4+ ions. Transport measurements indicated semiconductivity with an activation energy of 0.43 eV.