Obtaining glasses in the extremely crystallizing Ge-Sb-Te phase change material

Using thermal co-evaporation techniques, we show that various glassy compositions can be obtained along the GexSbxTe100-2x join in the ternary Ge-Sb-Te system which is known to display dramatic crystallization tendencies. Earlier attempts to produce bulk glasses have been limited to Sb-poor compositions close to the eutectic GeTe6. Results indicate a weak variation of T-g with composition x and also a thermal stability that is weak for most systems, and especially for compositions close to the domain where Ge2Sb2Te5 can be formed. Our results are put in perspective with other network-forming chalcogenides and the T-g variation suggests the preferential formation of Te-Sb-Te, at variance with isochemical compounds such as Ge-Sb-Se. Data are discussed within the framework of topological based approaches which not only indicate that optimal glass formation is achieved for compositions satisfying the Maxwell stability criterion but also predict a flexible to rigid transition at x = 8.5%. Most of our glasses could be formed around this composition.