Crystal/glass phase change in KSb₅S₈ studied through thermal analysis techniques

The reversible crystal-glass and glass-crystal transitions discovered in KSb₅S₈ were studied in detail with nonisothermal scanning calorimetry techniques. When cooled, molten KSb₅S₈ becomes a metastable glass, which can quantitatively revert to the crystalline form if heated above 277 °C. Crystalline KSb₅S₈ is a red semiconductor with a band gap of 1.82 eV, whereas the glass (also red) shows a lower but equally well-defined band gap of 1.67 eV. Two approaches have been used to analyze the glass transition. The activation energy of crystallization E_c was calculated using the Kissinger (∼167 ± 3.1 kJ/mol) and Flynn-Wall-Ozawa methods. The kinetic parameters and energy band gaps determined for KSb₅S₈ suggest possible utility of this system for phase-change, high-density optical data storage applications.