Neutron powder diffraction study of the rhombohedral to cubic phase transition in the series La_1-xPr_xAlO₃

Neutron powder diffraction has been used to examine the structural changes of the rare-earth aluminates La_1-xPr_xAlO₃ over a wide range of temperatures. At room temperature the aluminates adopt the rhombohedral perovskite structure in space group R3c. In all cases heating the sample results in a transition to cubic, the transition temperature increasing linearly with Pr content. The rhombohedral structure is characterised by rotation of the oxygen atom octahedra about the threefold axis. The maximum rotation angle also increases linearly with Pr content.