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

The crystal structures of the perovskite manganites Srx Ca1−x −y Ndy MnO3 with y =0.1 or 0.2 have been investigated using synchrotron X-ray powder diffraction. At room temperature the structures change from View the MathML sourcePm3¯m↔I4/mcm↔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 I 4/mcm to I 4/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 View the MathML sourcePm3¯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.