One-step synthesis of fine SrTiO3 particles using SrSO4 ore under alkaline hydrothermal conditions

The employment of mineral SrSO4 crystals and powders for preparing SrTiO3 compound was investigated, with coexistence of Ti(OH)4·4.5H2O gel under hydrothermal conditions, at various temperatures (150–250 °C) for different reaction intervals (0.08–96 h) in KOH solutions with different concentrations. The complete dissolution of the SrSO4 crystal occurred at 250 °C for 96 h in a 5 M KOH solution, resulting in the synthesis of SrTiO3 particles with two different shapes (peanut-like and cubic). In contrast, very fine SrTiO3 pseudospherical particles were crystallized when SrSO4 powders were employed as precursor. Variations on the SrTiO3 particle shape and size were found to be caused by the differences in the dissolution rate of the SrSO4 phase in the alkaline KOH solution. The crystallization of SrTiO3 particles was achieved by a bulk dissolution–precipitation mechanism of the raw precursors, and this mechanism was further accelerated by increasing the reaction temperature and concentration of the alkaline media. Kinetic data depicted that the activation energy required for the formation of SrTiO3 powders from the complete consumption of a SrSO4 single crystal plate under hydrothermal conditions, is 27.9 kJ mol−1. In contrast, when SrSO4 powders were employed (28–38 μm), the formation of SrTiO3 powder proceeded very fast even for a short reaction interval of 3 h at 250 °C in a 5 M KOH solution.