Abstract
The phase diagram of zinc (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 (hcp) crystal symmetry up to the melting temperature. The known decrease of the axial ratio (c/a) 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 c/a reaches (≈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 poly-crystals. In addition, a noticeable change in the pressure dependence of c/a 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: , where P is the pressure in GPa. The determined melt curve agrees with previous low-pressure studies and with shock-wave experiments, with a melting temperature of 5060(30) K at 135 GPa. Finally, a thermal equation of state is reported, which at room-temperature agrees with the literature.
Highlights
In the figure we represent the melt curve obtained from density-functional theory (DFT) calculations up to
We show a selection of x-ray diffraction (XRD) patterns measured at different pres sures, at temperatures between 455 and 470 K
We have shown that the known anisotropic compressibility of Zn at RT is repeated at high temperature
Summary
The behavior of structural and mechanical properties of metals under high-pressure (HP) and high-temperature (HT) conditions has received considerable attention for decades. The melt curve was determined up to 6 GPa from differential thermal analysis measurements in 1973 [24] After these pioneering works, a resurgence of interest in the behavior of Zn under HP conditions took place in 1995. Powder angle-dispersive XRD measurements were carried out following several P–T paths (described ) These experiments were conducted using the MSPD-BL04 beamline at the ALBA synchrotron [52] and the I15 beamline at diamond light source (DLS). Systems of 512 atoms (8 × 8 × 4) of different unit-cell volumes were used for the melting simulations, with a single Γ-point For such large systems, convergence to 2.5 meV/ atom was achieved in the whole interval of pressures, which corresponds to ~30 K uncertainty in the value of the corre sponding melting temperature. The discontinuity in the slope of c/a versus pressure can be clearly seen
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