Known weights of Cd, Zn and Te were reacted in silica optical cells of known volume, and the partial pressures of Te, and Cd between 485 and 1160 degrees C were determined by measuring the optical density of the vapor in the ultra-violet to visible range. The composition of the condensed phase or phases was calculated from the original weights and the amount of material in the vapor phase. The corresponding composition-temperature-partial pressures, x(Te) -T-P-Tc2,data, including five Te-rich solidus points, were established. The solubility range for the Te-rich Cd0.8Zn0.2Te(s) is similar to that of CdTe(s) with X-Te = 0.50005 at 809 degrees C and an estimated maximum solubility of X-Te = 0.50012 at about 1000 degrees C. The partial pressures of Cd and Te, measured over the Cd0.8Zn0.2Te melt at 1140 degrees C were about 1.55 and 0.02 atm, respectively, and the corresponding Zn partial pressure was estimated to be 0.05 atm. It was recommended that a Cd reservoir maintained at 800-820 degrees C should be used during directional solidification of Cd0.8Zn0.2Te to prevent the preferential loss of Cd to the vapor phase. (c) 2005 Elsevier B.V. All rights reserved.