High-pressure structural behavior of GdAlO3 and GdFeO3 perovskites

The orthorhombic perovskites, GdAlO3 and GdFeO3, have been studied using single-crystal X-ray diffraction up to 8.52 and 8.13GPa, respectively, in a diamond anvil cell at 298K. The evolution of the structures of GdAlO3 and GdFeO3 involves compression of both the GdO12 and the octahedral (AlO6 and FeO6) sites. The compression of the GdO12 site is anisotropic in both perovskites, with the four longest Gd-O distances compressing more than the eight shorter Gd-O bond lengths, resulting in a decrease in the distortion of GdO12 with pressure. In GdAlO3, the GdO12 site is less compressible than the AlO6 site, resulting in an increase of both the interoctahedral Al-O1-Al and Al-O2-Al angles with increasing pressure. Thus GdAlO3 perovskite becomes less distorted with increasing pressure. In GdFeO3, the GdO12 site displays a similar compressibility as the FeO6 site, with little change in the Fe-O2-Fe angle with pressure but an increase of the Fe-O1-Fe tilting angle. Thus GdFeO3 perovskite becomes less distorted with increasing pressure, but the change is not as pronounced as GdAlO3. The high-pressure behavior of GdAlO3 and GdFeO3 is similar to orthorhombic YAlO3 perovskite but contrasts with orthorhombic CaSnO3, which becomes more distorted with increasing pressure