Structural phase transitions in Pr1-xLaxAlO3: Heat capacity and x-ray scattering studies

Structural phase transitions in Pr1-xLaxAlO3 (0 ≤ x ≤ 1) single crystals have been studied through heat capacity and high-resolution x-ray scattering measurements. For PrAlO3, the heat capacity shows a sharp first-order peak at the rhombohedral to orthorhombic transition, while a classic mean-field anomaly is observed at the orthorhombic to monoclinic transition at lower temperatures. The transition temperature and the heat capacity anomaly of the two transitions diminish with increasing x, and only a single rhombohedral to monoclinic transition is observed for x = 0.8. Although this latter transition is required by group theory to be first order, no such evidence is found in the heat capacity and x-ray scattering measurements. Instead, the results are consistent with mean-field criticality, with a small distribution of transition temperature originating from weak disorder.