Pressure-induced structural change in orthorhombic perovskite GdMnO3

Structural stability of the perovskite-type GdMnO3 has been investigated by the synchrotron angle-dispersive x-ray diffraction technique up to 63 GPa in a diamond anvil cell. GdMnO3 stays in an orthorhombic structure but undergoes an isostructural phase transition with similar to 5% volume reduction at 50 GPa. In the parent orthorhombic phase, the compressions along a, b and c axes exhibit a large anisotropic behavior. With increasing pressure, our results show that the distortion and tilts of the MnO6 octahedra are reduced continuously and the orthorhombic structure evolves towards higher symmetry. By fitting the observed pressure-volume data using the third-order Birch-Murnaghan equation of state, we obtain the bulk modulus B-0 = 156(3) GPa with B-0' = 6.5(3) for the starting orthorhombic phase. Upon decompression, the starting orthorhombic phase is recovered.