Phase Equilibria in the TeO2-CdI2 System

Abstract

Using differential thermal analysis, x-ray diffraction analysis and density measurements the phase diagram of the TeO2-CdI2 system is built. It is characterized with four non-variant equilibria: the temperatures of the eutectic, monotectic, peritectic and peritectoidal points are at 345, 565, 470 and 240 °C, respectively. As a result of the passing of peritectic and peritectoidal reactions, two intermediate compounds with composition CdI2·3TeO2 (A) and 2CdI2·3TeO2 (B) are formed, both crystallizing in monoclinic lattice system with near unit cell parameters. The intermediate compounds A and B possess narrow solid-solution regions. The B passes through polymorphous transition, which, depending on the composition, varies between 245 and 265 °C. The two intermediate compounds, together with the initial TeO2 and CdI2, determine the presence of 16 phase fields: 5 monophase (melt L, α-TeO2, β-B, α-A and α-B) and 11 two-phase. These characteristics of the phase diagram of the TeO2-CdI2 system (two intermediate compounds with complicated compositions CdI2·3TeO2 and 2CdI2·3TeO2, two low-temperature eutectic and monotectic transitions at TE = 345 and TM = 570 °C, respectively, are sufficient precondition for obtaining of new oxychalcohalide glasses with wide region of glass formation in three-component systems from the MenChm-TeO2-CdI2 kind (MenChm—glassformer).