The pressure-induced phase transition in zinc sulfide is studied using a constant-pressure ab initio technique. The reversible phase transition from the zinc-blende structure to a rock-salt structure is successfully reproduced through the simulations. The transformation mechanism at the atomistic level is characterized and found to be due to a monoclinic modification of the simulation cell, similar to that obtained in SiC. This observation supports the universal transition state of high-pressure zinc-blende to rock-salt transition in semiconductor compounds. We also study the role of stress deviations on the transformation mechanism and find that the system follows the same transition pathway under nonhydrostatic compressions as well.

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Using powder X-ray diffraction and AC impedance spectroscopy, we have found that the superprotonic CsH2PO4 (CDP) phase is stable at T = 250 °C when sealed in different volumes (15 mL and 50 mL) of dry air or inert gasses. Under these conditions, CDP’s proton conductivity stays constant at 2.5 × 10−2 S·cm−1 for at least 10 h. On the other hand, removing the gas from the chamber leads to a sharp, two-order-of-magnitude drop in the proton conductivity. Our data show no evidence of a self-generated water vapor atmosphere in the chamber, and the gas pressure at T = 250 °C is several orders of magnitude below the pressures previously used to stabilize CDP’s superprotonic phase. These results demonstrate that hermetically sealing CDP in small gas-filled volumes represents a new method to stabilize the superprotonic phase, which opens new paths for large-scale applications of phosphate-based solid acids as fuel cell electrolytes.