High-pressure high-temperature phase diagram of zinc

TL;DR

This study maps the phase diagram of zinc up to 140 GPa and 6000 K, revealing a stable hcp structure, a pressure-induced axial ratio change, and an extended melt curve consistent with previous data.

Contribution

It provides new high-pressure, high-temperature phase diagram data for zinc, including a detailed melt curve and evidence of a possible pressure-induced phase transition.

Findings

Zinc retains hcp structure up to melting.

Axial ratio decreases with pressure, reaching sqrt(3) around 10 GPa.

Melt temperature at 135 GPa is approximately 5060 K.

Abstract

The phase diagram of Zn has been explored up to 140 GPa and 6000 K, by combining optical observations, x-ray diffraction, and ab-initio calculations. In the pressure range covered by this study, Zn is found to retain a hexagonal close-packed crystal symmetry up to the melting temperature. The known decrease of the axial ratio of the hcp phase of Zn under compression is observed in x-ray diffraction experiments from 300 K up to the melting temperature. The pressure at which the axial ratio reaches the square root of 3 value, around 10 GPa, is slightly affected by temperature. When this axial ratio is reached, we observed that single crystals of Zn, formed at high temperature, break into multiple polycrystals. In addition, a noticeable change in the pressure dependence of the axial ratio takes place at the same pressure. Both phenomena could be caused by an isomorphic second-order phase transition induced by pressure in Zn. The reported melt curve extends previous results from 24 to 135 GPa. The pressure dependence obtained for the melting temperature is accurately described up to 135 GPa by using a Simon-Glatzel equation. The determined melt curve agrees with previous low-pressure studies and with shock-wave experiments, with a melting temperature of 5060 K at 135 GPa. Finally, a thermal equation of state is reported, which at room-temperature agrees with the literature.