The Temperature‐Composition Phase Equilibria in the HgTe–HgI₂Pseudobinary System

Abstract

The temperature‐composition phase diagram of the HgTe—HgI2 pseudobinary system was determined between 25 and 670°C using differential scanning calorimetry, differential thermal analysis, Debye‐Scherrer powder X‐ray diffraction techniques, and metallographic analysis methods. Solid solutions of HgTe and HgI2 with the cubic, zinc blende‐type structure exist above 300°C, having a maximum solubility of 11.7±0.8 Mol‐% HgI2 in HgTe at 501±5°C. The monoclinic intermediate phase Hg3Te2I2 is formed by a peritectic reaction upon cooling at 501±5°C, with the peritectic point at approximately 37±4 Mol‐% HgI2. The previously unknown cubic phase Hg3TeI4 (a = 6.240±0.003 Å) is formed by a eutectoid reaction at 238±3°C and is stable up to 273±3°C, where it melts by a peritectic reaction with the peritectic point at approximately 79±3 Mol‐% HgI2. Between Hg3TeI4 and HgI2 is a eutectic point at 82±3 Mol‐% HgI2 and 250±3°C. The α to β transition of HgI2 at 133±3°C is independent of sample composition between 33.3 and 100 Mol‐% HgI2.

The Temperature-Composition Phase Equilibria in the Hg0.8Cd0.2Te-HgI2 Pseudobinary SystemBased on part of a thesis to be submitted by M. A. Hutchins to the Graduate School of Rensselaer Polytechnic Institute in partial fulfillment of the requirements for a Ph.D. degree.Dedicated to Professor Welf Bronger on the Occasion of his 70th Birthday

“…This value is significantly greater than the above mentioned solubility of HgI 2 in HgTe [18]. The observations of this work are compared to those of the earlier investigations of the related CdTe-HgI 2 [17], HgTe-HgI 2 [18,19] and of the preliminary studies [21] of the present system. The present investigation of the Hg 0.8 Cd 0.2 Te-HgI 2 temperature-composition phase diagram is mainly concerned with the region between 0 and 40 mole-% HgI 2 .…”

“…In earlier phase diagram studies of the related HgTe-HgI 2 [16] and CdTe-HgI 2 [17] systems, no solubility of HgI 2 in HgTe or CdTe was observed. During the latter investigation [19], the formation of the previously unknown cubic phase Hg 3 TeI 4 was observed, the structure of which was recently determined [20]. During the latter investigation [19], the formation of the previously unknown cubic phase Hg 3 TeI 4 was observed, the structure of which was recently determined [20].…”

“…Several sets of such ampoules were prepared, in which the compositions of the starting mixtures ranged from pure Hg 0.8 Cd 0.2 Te to pure HgI 2 in 0.5, 1, 2, 3, 4, and 5 mole-% HgI 2 increments. The annealing times used are sufficient for the samples to reach equilibrium, based on the earlier studies of the solubility of HgI 2 in HgTe [18,19] and in Hg 0.8 Cd 0.2 Te [21], and based on diffusion rate estimations. In order to reduce the equilibration time, some samples were initially annealed above their final temperature for up to three days.…”

“…Samples with nominal compositions between 3 and 40 mole-% HgI 2 , in 3 and 5 mole-% increments, were annealed in a horizontal furnace at 600°C for 1.5 days and at 403°C for 17 days, and then quenched in cold water. The final annealing temperature of 110°C was selected for these samples because it is below the α to β transition temperature of pure HgI 2 at 133 ± 3°C [19]. Samples with nominal compositions between 40 and 95 mole-% HgI 2 , in 5 mole-% increments, were annealed in a horizontal furnace for 2 days each at 272°C, 283°C, and at 503°C, 4 hours at 450°C, 18 hours at 400°C, 2 days at 350°C, 1 day at 300°C, 2 days at 250°C, 1 day at 200°C, 61 days at 120°C, and 44 days at 110°C, after which the samples were quenched in cold water.…”

“…The procedures of the DSC measurements, including instrument calibration, sample pans, and pan sealing steps, were identical to those described earlier [19] for the HgTe-HgI 2 system. 2.2 and 2.3) were also analyzed by differential scanning calorimetry (DSC).…”