High-temperature structural phase transition in Ca0.7Ti0.7La0.3Al0.3O3: investigation by synchrotron x-ray diffraction

Mixed-oxide prepared Ca0.7Ti0.7La0.3Al0.3O3 (CTLA) ceramics (≈96% dense), grain size 6–7 μm, with dielectric properties (at 4 GHz) of ɛr≈46, Q×f≈38 000 GHz, and τf+13 ppm/°C, were studied at 25°–1300°C using synchrotron X-ray powder diffraction. At room temperature, CTLA exhibits a distorted orthorhombic structure, with two tilt systems: a=5.40383 (4) Å, b=5.41106 (6) Å, and c=7.64114 (7) Å with space group Pbnm. At 1050°±25°C, there is a transition from orthorhombic (Pbnm) to tetragonal (I4/mcm), with a simpler tilt arrangement. The lattice parameters at 1100°C were: a=5.44285 (4) Å and c=7.68913 (8) Å.