Synthesis and Structural Studies of the Transition-Metal-Doped Rh Perovskites LaMn0.5Rh0.5O3 and LaCu0.5Rh0.5O3

The two orthorhombic perovskites LaMn0.5Rh0.5O3 and LaCu0.5Rh0.5O3 have been characterized using X-ray absorption near edge structure (XANES) measurements and powder synchrotron X-ray and neutron diffraction. The Mn and Rh in LaMn0.5Rh0.5O3 are essentially trivalent and disordered onto the same crystallographic site. The absence of an appreciable Jahn−Teller (JT) distortion of the BO6 octahedra is a consequence of this disorder and large magnitude of the octahedral tilting. XANES measurements show that the Rh in LaCu0.5Rh0.5O3 has a valence state of around +3.5 as a consequence of extensive charge delocalization between the Cu and Rh cations, that are also disordered onto a single site. These two effects combine to further reduce the distortion of the octahedra in LaCu0.5Rh0.5O3 relative to that of LaMn0.5Rh0.5O3.