Study of the optically diffused reflectance and thermal-microstructure for the phase transformation of AgNO_3

摘要

Optical, microstructural, and thermal properties of the investigated silver nitrate samples were characterized by various techniques, such as X-ray analysis, scanning electron microscopy, UV-Vis-NIR absorption and differential scanning calorimetry (DSC). The presence of structural phase transition [orthorhombic structure (phase Ⅱ) to rhombohedral structure (phase Ⅰ)] was checked by DSC and X-ray analysis measurements. The thermal energy required for such transformation is found to be 11.6 J/g. The optical band gaps of AgNO_3 are 1.4 and 2.02 eV for phase Ⅱ and phase Ⅰ, respectively, at the low-energy region. But at high-energy region, the optical band gaps are 3.41 and 3.43 eV for phase Ⅱ and phase Ⅰ, respectively. Characteristic peaks for AgNO_3 corresponding to (2 1 1), (0 0 4) and (3 5 1) for phase Ⅱ and (0 0 4), (3 1 1) and (0 2 4) for phase Ⅰ have been observed. The average crystalline size for AgNO_3 samples and the values of dislocation density δ and the strain ε for the planes of two phases Ⅱ and Ⅰ are calculated and also the texture coefficient is determined. Such information can considerably aid in understanding the process of phase transformations in AgNO_3.