Structural characterisation of the perovskite series SrxCa1-x-yNdyMnO3: Influence of the Jahn-Teller effect

The crystal structures of the perovskite manganites SrxCa1-x-yNdyMnO3 with y=0.1 or 0.2 have been investigated using synchrotron X-ray powder diffraction. At room temperature the structures change from Pm over(3, -) m â?? I 4 / mcm â?? Pbnm depending on the cation distribution, the different structures exhibiting different tilts of the MnO6 octahedra. High temperature diffraction measurements demonstrate the presence of, an apparently continuous, isosymmetric I4/mcm to I4/mcm phase transition associated with the removal of long range orbital ordering. Heating the manganites to still higher temperatures results in a continuous transition to the cubic Pm over(3, -) m structure. A feature of such transitions is the continuous evolution of the octahedral tilt angle through the I4/mcm to I4/mcm phase transition. The orthorhombic structures do not exhibit orbital ordering and although a first order transition to the tetragonal structure is observed in Sr0.4Ca0.5Nd0.1MnO3, this high temperature tetragonal structure does not exhibit orbital ordering. © 2009 Elsevier Inc. All rights reserved.