Novel borides of the boron filled β-Mn-type structure

Abstract

The existence of a boron-filled β-Mn-type compound has been observed for the first time in the Pd-Cu-B system. The crystal structure of this phase, its homogeneity field and phase equilibria in the relevant compositional range have been examined by electron probe microanalysis, and single crystal and powder X-ray diffraction of alloys annealed at 650 °C for 240 h. The B-filled β-Mn-type structure has been found to exist within ∼50 at% - ∼57 at% Pd at 60–80% boron population in [Pd6] octahedral voids (B in 4a). Metal atom ordering (Mo3Al2C-type structure, Pd in 12d, Cu in 8c, B in 4a) has been proved from single crystal data in Pd3Cu2B0.8 at 80% boron population of the 4a boron atom sites. The structures of the B-filled β-Mn-type samples in the Pd-Cu-B system exhibit preferential occupation of the 12d Wyckoff position by the more electronegative element with larger atomic radius, i.e. Pd. Metallic behavior of this phase was ascertained by measurements of electrical resistivity. No superconductivity has been observed from electrical resistivity measurements down to 0.3 K. Ab initio electronic structure calculations indicate a rather low electronic density of states at the Fermi level for Pd3Cu2B, with the palladium d-states contributing almost 50% to the total density. The band structure of Pd3Cu2B exhibits multiple bands intersecting the Fermi energy.