Structural and Electronic Phase Transitions in Mixed Transition Metal Perovskite Oxides

Abstract

The reported multiferroic perovskite series Sr1-xAxTi1/2Mn1/2O3 has been the subject of numerous structural studies, without reaching consensus. In the current work, the cubic Pm3 ̅m is confirmed for end member SrTi1/2Mn1/2O3 in the Sr1-xAxTi1/2Mn1/2O3 ( A= Ca, La; 0 ≤ x ≤ 1) series. The Pm3 ̅m  I4/mcm  Pbnm structural evolution was observed with increased doping level of Ca. A cubic Pm3 ̅m  rhombohedral R3 ̅c transition occurred when La is substituted instead of Ca. Interesting magnetic behaviours were observed and the major contribution to this was concluded to be the mixed Mn4+/Mn3+ ratio. Ru and Ir have almost identical ionic radii and behave similarly in many ways. Remarkably the structure and properties of SrRuO3 and SrIrO3 are different. The current study revealed that the divalent transition metal doped materials of the type SrR1-xMxO3 (R = Ru, Ir, and M = 3d transition metals) are isostructural. This was achieved by the synthesis of a number of new materials of the type SrIr1-xMxO3. Therefore, these two series are comparatively described in the thesis. The structure and physical properties of the iron doped series SrIr1-xFexO3 are found to be different from those of the divalent doped ones, and this was even true for Ru analogues. Therefore, Fe-doped SrRuO3 and SrIrO3, based on the results of the same level doped materials are presented in a separate chapter. In the final chapter, the impact of Cu2+ doping on the structure and electronic properties of LaCrO3 is described. In order to understand structure property relationships, all the materials structurally characterised have had magnetic and resistivity measurements conducted. Special attention is given to realise the correlations between structure, magnetism, and conductivity.