Solvothermal Preparation and Thermal Phase Change Behaviors of Nanosized Tetragonal-Phase Silver Selenide (Ag<sub>2</sub>Se)

Nanocrystalline silver selenide (Ag 2 Se) 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 Ag 2 Se. Room-temperature powder X-ray diffraction (XRD) measurements indicated that the as-prepared Ag 2 Se 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 Ag 2 Se nanocrystals, and the results showed that the low-temperature tetragonal phase transforms to the high-temperature cubic phase at about 106 °C. This transition temperature is lower by ~30 °C than the orthorhombic-cubic transition temperature (133140 °C) previously reported for Ag 2 Se. Meanwhile, two exothermic peaks, loaded at 61 and 89 °C, respectively, were detected in the cooling DSC scan for the cubic to tetragonal phase transition, and the reason was discussed.