Crystal structures and phase transitions of orthorhombic and rhombohedral RGaO3(R=La,Pr,Nd) investigated by neutron powder diffraction

The rare-earth gallium oxide perovskites RGaO 3 (R=La,Pr,Nd) are promising substrates for epitaxy of high-T c superconductors. In this paper the crystal structures of orthorhombic and rhombohedral RGaO 3 have been studied by neutron diffraction, which allows precise localization of light atoms such as oxygen, which are of importance in phase transitions. The lattice parameters, atom positions and tilt angles of the oxygen octahedra were determined in the temperature range 12-1773 K. Lanthanum gallate LaGaO 3 shows a phase transition from an orthorhombic phase (Pbnm) to a rhombohedral phase (Rc) at 425 K. The results are discussed in the classification schemes developed for distorted perovskites.