High-pressure single-crystal X-ray diffraction study of YAlO3 perovskite

The equation of state and structural changes of YAlO3 perovskite, a GdFeO3-type perovskite with Pbnm symmetry, have been investigated to 8.5 GPa in a diamond-anvil cell at room temperature using single-crystal X-ray diffraction. A fit of a third-order Birch-Murnaghan equation of state to the P-V data yields values of K-TO = 192(2) GPa and K-0(1) = 7.3(4), with compressional moduli of the axes, K-a0 = 220(7) GPa, K-bO = 157(3) GPa and K-cO = 212(2) GPa, and their pressure derivatives, K-aO(1) = 12(2); K-bO(1) = 4.4(6)(6) and K-cO(1) = 8.7(4). The evolution of the structure with pressure shows that compression of the YO12 site is strongly anisotropic with the four longest Y-O separations more compressible than the eight shorter Y-O bond lengths. Consequently the distortion of the YO12 site decreases with increasing pressure. In contrast, the A1O6 site undergoes nearly isotropic compression and is more compressible than the YO12 site. The interoctahedral angles, angle A1-O1-Al and angle A1-O2-A1, show a significant increase with pressure, reflected in the movement of 01 along <100>. The structure of YAIO(3) perovskite therefore becomes less distorted with increasing pressure, in contrast with other Pbnm perovskites such as CaSnO3 (C) 2003 Elsevier Inc. All rights reserved.