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 Ec was calculated using the Kissinger (~167 (plus_minus) 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 phasechange, high-density optical data storage applications