From β-Phase Particle to α-Phase Hexagonal-Platelet Superstructure over AgGaO2: Phase Transformation, Formation Mechanism of Morphology, and Photocatalytic Properties

We studied an orthorhombic-to-rhombohedral transformation of AgGaO2, which was performed in water at low temperature and accompanied by morphology variation, by using powder X-ray diffraction, UV-visible absorption spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, and photocatalytic 2-propanol oxidization. The experimental results revealed that the crystal growth of the beta-phase (orthorhombic AgGaO2) to alpha-phase (rhombohedral AgGaO2) in water could be divided into phase-transformation, transition, and mature periods. The effects of water and temperature on the phase transformation and crystal-structure correction were clarified. It is found that the morphology of the alpha-phase sample is a superstructure, the shape of which is influenced by the phase-transformation temperature. The morphology variation of beta-phase particle to alpha-phase hexagonal platelet is a solid-liquid-solid growth process via the time-line based SEM images. The formation mechanism of this superstructure may be attributed to the growing-space competition.