A new way of phase identification, of AgGaGeS{sub 4}∙nGeS{sub 2} crystals

• Published in: Journal of solid state chemistry Vol. 203
• Main Authors: Nikolaev, R.E., Vasilyeva, I.G.
• Format: Journal Article
• Language: English
• Published: United States 15.07.2013
• Subjects: CRYSTALLIZATION; CRYSTALS; DECOMPOSITION; DENSITY; DETECTION; GERMANIUM SULFIDES; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MELTING POINTS; SOLID SOLUTIONS; X-RAY DIFFRACTION; X-RAY SPECTROSCOPY
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/J.JSSC.2013.05.002

The phase identification of AgGaGeS{sub 4}·nGeS{sub 2} (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 GeS{sub 2}. 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 GeS{sub 2} and heterogeneous state of the crystals. The boundary value n=1.5 at 1045 K and the coexistence of the solid solution AgGaGeS{sub 4}·1.5GeS{sub 2} with the β-GeS{sub 2} phase for n>1.5 was found. Glassy GeS{sub 2} (∼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 GeS{sub 2} was measured by the vapor pressure measurements. - Graphical abstract: lg p–1/T dependences of as-grown AgGaGeS{sub 4}·nGeS{sub 2} crystals. - Highlights: • Vapor pressure measurement as a powerful tool of phase identification. • Thermal characteristics of glassy GeS{sub 2}. • The homogeneity range of AgGaGeS{sub 4} from the GeS{sub 2} side.