Crystal/Glass Phase Change in KSb5S8 Studied through Thermal Analysis Techniques

The reversible crystal−glass and glass−crystal transitions discovered in KSb 5 S 8 were studied in detail with nonisothermal scanning calorimetry techniques. When cooled, molten KSb 5 S 8 becomes a metastable glass, which can quantitatively revert to the crystalline form if heated above 277 °C. Crystalline KSb 5 S 8 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 KSb 5 S 8 suggest possible utility of this system for phase-change, high-density optical data storage applications.