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 Mg 3+ x Ni 7− x B 2 in the B–Mg–Ni system. The Mg 3+ x Ni 7− x B 2 phase was prepared by solid-state reactions at 1073 K and its crystal structure was determined and refined using X-ray powder diffraction data. The Mg 3+ x Ni 7− x B 2 phase crystallizes in the Ca 3 Ni 7 B 2 structure type (space group R-3m, no. 166) with a =4.9496(3)–5.0105(6) A, c =20.480(1)–20.581(1) A depending on the x value, where x varies from 0.17 to 0.66. Two samples with nominal compositions Mg 10 Ni 20 B 6 and Mg 12 Ni 18 B 6 were characterized by magnetization and electric resistivity measurements in the temperature range from 5 K to room temperature. Both samples exhibited metallic behavior and showed spin-glass-like behavior with a spin freezing temperature ( T f ) around 33 K. A study of the Cu-doping effect showed that limited Cu content can be doped into the Mg 3+ x Ni 7− x B 2 compound and T f decreases as the Cu content increases.