Structure characteristics and valence state study for La_1-xNa_xTiO₃ synthesized under high-pressure and high-temperature conditions

By using a novel high-pressure, high-temperature method, perovskite oxides of La_1-xNa_xTiO₃ (x = 0.05, 0.1-0.8) with mixed valence state were synthesized. XRD analysis shows a cubic cell for the samples. Cell volumes of the samples with 0.1≤x≤0.5 decreases as x increases, and the cell volume for x = 0.05 is smaller than that for x = 0.1. XPS of surface and EPR measurements indicate that Ti ions are of mixed valence of +3 and +4 and that A-cations vacancies exist in the samples. As x increases, the amount of Ti³⁺ ions decreases and the amount of A-cations vacancies increases. The valence state of Ti ions can be altered by changing both pressure and temperature.