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 AgGaO 2, 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 β-phase (orthorhombic AgGaO 2 ) to α-phase (rhombohedral AgGaO 2 ) 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 α-phase sample is a superstructure, the shape of which is influenced by the phase-transformation temperature. The morphology variation of β-phase particle to α-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.