Solvothermal Preparation and Thermal Phase Change Behaviors of Nanosized Tetragonal-Phase Silver Selenide (Ag2Se)

Nanocrystalline silver selenide (Ag2Se) with an average diameter of 100 nm were prepared by a facile solvothermal method. X-ray energy dispersive (EDS) spectroscopy and X-ray photoelectron spectroscopy (XPS) studies confirmed that the products were pure Ag2Se. Room-temperature powder X-ray diffraction (XRD) measurements indicated that the as-prepared Ag2Se nanocrystals exhibit a metastable tetragonal polymorphic phase, rather than the common orthorhombic phase at room temperature. The variable-temperature XRD and differential scanning calorimetry (DSC) thermal analysis techniques were used to investigate the phase change behaviors of the tetragonal Ag2Se nanocrystals, and the results showed that the low-temperature tetragonal phase transforms to the high-temperature cubic phase at about 106 degrees C. This transition temperature is lower by similar to 30 degrees C than the orthorhombic-cubic transition temperature (133-140 degrees C) previously reported for Ag2Se. Meanwhile, two exothermic peaks, loaded at 61 and 89 degrees C, respectively, were detected in the cooling DSC scan for the cubic to tetragonal phase transition, and the reason was discussed.