Study of the Diffused Reflectance and Microstructure for the Phase Transformation of $KNO_{3}$

Optical, micro-structural, thermal and electrical properties of the investigated potassium nitrate ($KNO_{3}$) samples were characterized by various techniques such as X-ray analysis, scanning electron microscopy, UV-VIS-NIR absorption and differential scanning calorimetry. The presence of structural phase transition is checked by differential scanning calorimetry, electrical and X-ray analysis measurement. The thermal energy required for such transformation is calculated and found to be 46.2 J/g. The activation energies of the electrical conduction for $KNO_{3}$ were found to be 0.236 eV for phase II and 0.967 eV for phase I. The optical band gaps of $KNO_{3}$ for the higher photon energy are calculated and equal to 5.03 and 5.01 eV for II and I phases, respectively and at lower photon energy, the values are equal to 3.84 and 3.80 eV for II and I phases, respectively. The data which leads to the interpretation of electronic spectra of potassium nitrate is possible to assume that the long wavelength part of absorption band corresponds to n-π* transition. Then, the short-wavelength part is probably due to the transition in a higher excited state of symmetry π-π*. The mean values of crystalline sizes are determined by scanning electron microscopy analysis. Such information can considerably aid in understanding the process of transformations near the phase crystal modifications at 129°C.