Physical properties of the V-Al5Cu6Mg2 complex intermetallic phase

Abstract

The cubic V-Al5Cu6Mg2 phase with 39 atoms in the unit cell is an intermetallic phase with intermediate structural complexity between the simple Laves phase and the complex Bergman phase. Using 27Al NMR spectroscopy, we have determined the electric-field-gradient tensors at the positions of three crystallographically nonequivalent Al sites in the unit cell and confirmed the local site symmetries of these sites, as predicted by the Samson structural model of the V-phase from 1949. The influence of structural complexity on the physical properties of a solid was studied by determining bulk electrical and thermal properties (electrical resistivity, thermoelectric power, Hall coefficient, thermal conductivity and specific heat) and local electronic properties of the V-Al5Cu6Mg2 monocrystal by studying the 27Al NMR Knight shift and the spin-lattice relaxation rate. The experiments reveal that free-electron picture is good approximation to the V-Al5Cu6Mg2 electronic structure, despite the structural complexity of the lattice. The positive thermopower and Hall coefficient reveal that V-Al5Cu6Mg2 is a hole-type electrical conductor. Electrical resistivity shows linear temperature dependence with a positive temperature coefficient, typical of regular metals and alloys. The relatively large T→0 residual resistivity and the low thermal conductivity suggest the presence of quenched structural disorder, very likely intrinsic to the V-Al5Cu6Mg2 structure. We did not find any experimental evidence of a pseudogap close to the Fermi energy in the electronic density of states that could contribute to the electronic stabilization of the structure.