The structure of lithium-magnesium solid solutions—I: Measurements on the Bragg reflections

Abstract

Lattice parameters have been measured at 20°C and −183°C for seven BCC Li-Mg alloys. There is a strong negative deviation from Vegard's law and a minimum in the parameter-composition curve at 65 atomic per cent Li. Two measurements have been made on martensitic FCC Li-Mg alloy's at −183°C, and a negative deviation from Vegard's law is also indicated for these alloys. In the HCP solid solutions of Li in Mg. both the a and c axes decrease with increasing Li content, while the c a ratio decreases from 1.6235 for pure Mg to 1.608 at 18.4 atomic per cent Li (the α α + β phase boundary). The presence of local static displacements of the atoms from the sites of the average lattice has been demonstrated from measurements of the Bragg intensities at 295°K and 90°K. These intensity measurements have also been used to derive values of the Debye characteristic temperature for five BCC alloys.