Effect of Very High Pressure on the Structure of Some hcp Metals and Alloys

Abstract

The effect of pressure up to several hundred kilobars has been measured on the lattice parameters of a number of hcp metals and alloys including magnesium and six dilute alloys, cadmium and two alloys, two alloys of silver with indium and two with antimony, and the rare-earth metals holmium, erbium, and thulium. For magnesium and its alloys the x-ray data combined with resistance data give rather clear evidence for a transition at high pressure from hcp to dhcp (ABABAB\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}to ABACABAC\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}). Electrical resistance measurements on pure cadmium indicate a similar event. No transition is noted for the cadmium alloys. All four silver alloys underwent a similar transition at high pressure. The rare earths show a high-pressure transition accompanied by an increase in the lattice parameter $c$ with increasing pressure, which may be related to those appearing in the group II metals and the silver alloys.