One-step synthesis of fine SrTiO 3 particles using SrSO 4 ore under alkaline hydrothermal conditions

Abstract

The employment of mineral SrSO 4 crystals and powders for preparing SrTiO 3 compound was investigated, with coexistence of Ti(OH) 4·4.5H 2O 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 SrSO 4 crystal occurred at 250 °C for 96 h in a 5 M KOH solution, resulting in the synthesis of SrTiO 3 particles with two different shapes (peanut-like and cubic). In contrast, very fine SrTiO 3 pseudospherical particles were crystallized when SrSO 4 powders were employed as precursor. Variations on the SrTiO 3 particle shape and size were found to be caused by the differences in the dissolution rate of the SrSO 4 phase in the alkaline KOH solution. The crystallization of SrTiO 3 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 SrTiO 3 powders from the complete consumption of a SrSO 4 single crystal plate under hydrothermal conditions, is 27.9 kJ mol −1. In contrast, when SrSO 4 powders were employed (28–38 μm), the formation of SrTiO 3 powder proceeded very fast even for a short reaction interval of 3 h at 250 °C in a 5 M KOH solution.