Construction of Structural Phase Diagram of LaGa1−xMgxO3−δ by Using Various Diffraction Measurements and Thermal Analyses—Effect of Long Period Anti-Phase Domain Structure on Phase Diagram—

Construction of structural phase diagram of LaGa1−xMgxO3−δ has been attempted by using synchrotron X-ray diffraction, high temperature X-ray diffraction, dilatometry and differential scanning calorimetry. Existence of long-period anti-phase domain structure(LPAPDS) observed in the specimens with x larger than 0.10 by using electron diffraction analysis was considered for the phase diagram construction. Existence of four phases has been proposed and their phase relationship has been evaluated. For the specimen with x≈0.00, orthorhombic phase free from LPAPDS and rhombohedral phase without LPAPDS were detected. In LaGa1−xMgxO3−δ with x larger than 0.10, orthorhombic phase and rhombohedral phase with LPAPDS were proposed. It was suggested that the slow kinetics of the phase transition from orthorhombic phase with LPAPDS to rhombohedral with LPAPDS was the origin of region, where mixture of orthorhombic phase and rhombohedral phase was observed. Existence of two-phase region, where phase free from LPAPDS and one with LPAPDS coexist, has been clarified. The compositional region, where x is around 0.05, is revealed to be the two-phase region from room temperature to 800°C.