Preparation and properties of a new ternary phase Mg3+xNi7−xB2 (0.17≤x≤0.66) and its Cu-doping effect

Abstract

In recent years, the materials in the B–Mg–Ni system have been intensively studied due to their excellent properties of hydrogen storage and superconductivity. Solving the crystal structure of phases in this system will facilitate an understanding of the mechanism of their physical properties. In this study, we report the preparation, crystal structure and physical properties of a new ternary phase Mg3+xNi7−xB2 in the B–Mg–Ni system. The Mg3+xNi7−xB2 phase was prepared by solid-state reactions at 1073K and its crystal structure was determined and refined using X-ray powder diffraction data. The Mg3+xNi7−xB2 phase crystallizes in the Ca3Ni7B2 structure type (space group R-3m, no. 166) with a=4.9496(3)–5.0105(6) Å, c=20.480(1)–20.581(1) Å depending on the x value, where x varies from 0.17 to 0.66. Two samples with nominal compositions Mg10Ni20B6 and Mg12Ni18B6 were characterized by magnetization and electric resistivity measurements in the temperature range from 5K to room temperature. Both samples exhibited metallic behavior and showed spin-glass-like behavior with a spin freezing temperature (Tf) around 33K. A study of the Cu-doping effect showed that limited Cu content can be doped into the Mg3+xNi7−xB2 compound and Tf decreases as the Cu content increases.