A new way of phase identification, of AgGaGeS4∙nGeS2 crystals

Abstract

The phase identification of AgGaGeS4·nGeS2 (n=0–4) crystals grown by vertical Bridgman–Stockbarger technique was carried out to find the boundary value n between a homogeneous solid solution and its mixture with GeS2. To obtain reliable results, the conventional methods of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) were completed by less common vapor pressure measurement in a closed volume and precise density measurements, which are very sensitive to the detection of small amounts of crystalline and glassy GeS2 and heterogeneous state of the crystals. The boundary value n=1.5 at 1045 K and the coexistence of the solid solution AgGaGeS4·1.5GeS2 with the β-GeS2 phase for n>1.5 was found. Glassy GeS2 (~2 mol%) was revealed by vapor pressure measurement and XRD studies in all the crystals. This is discussed in terms of the supersaturated solid solution decomposition upon temperature decreasing and the microphase separation of overcooled melt near the melting point under non-equilibrium crystallization. For the first time, the p–T dependence for glassy GeS2 was measured by the vapor pressure measurements.