High-Pressure Phase-Equilibrium Studies of CdS and MnS by Static and Dynamic Methods

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Abstract
The P‐T equilibrium of CdS polymorphs was studied in the range to over 50 kbar and 700°C in opposedanvil and hydrothermal pressure apparatuses. Use of CdS of diverse origins revealed important effects of structure, preparations, and mechanical treatment on polymorphic transitions, especially noticeable in electrical resistance discontinuities with pressure or temperature changes. A triple point was located at 425°±5°C and 16.5±0.5 kbar between the phase fields of CdS‐I (wurtzite, and also CdS‐I′, metastable sphalerite), CdS‐II (rocksalt structure) and CdS‐III (a new polymorph, presumably of B23 structure). The slopes of the I to II, I to III, and II to III phase boundaries are 130°, −47°, and 1.6°C/kbar, respectively. Resistivity of the II phase was found not to be ``metallic.'' The large drop in resistance during the I–II reconstructive transformation is attributed to a grain boundary conduction mechanism. The P‐T‐X of the system MnS‐CdS was determined to 600°C and 40 kbar. A maximum of 80 mol % CdS was found in a quenchable II phase, but the III phase could not be quenched at any composition.