Abstract
The structural transformation from the cubic to tetragonal phase has been studied in near-equiatomic M-Ru (M=V, Nb, Ta) alloys through the measurements of electrical resistivity, Hall coefficient and low-temperature specific heat. The transformation temperature TL decreases with decreasing Ru concentration. The values of TL for the binary V-Ru system and the pseudobinary V-Ti-Ru system are universally dependent on the electron-atom ratio Z, indicating the electronic transition. On the other hand, for pseudobinary M-Ti-Ru (M=Nb, Ta) systems, the TL values are not expressed as universal functions of Z. The Hall coefficient RH for V50+xRu50−x alloys decreases in the tetragonal phase, while it increases in the cubic phase with increasing the composition x, showing a minimum at the boundary composition between the cubic and tetragonal phases. For Nb50+xRu50−x and Ta50+xRu50−x alloys, on the contrary, the RH decreases monotonically with increasing x, showing no peak at the boundary composition. The value of electronic specific-heat coefficient γ for V54Ru46 is 7.5 mJ·mol−1·K−2, which is 4.2 times γ for Nb54Ru46 and 7.5 times γ for Ta54Ru46. The values of Debye temperature θD turn out to be 420 K for V54Ru46, 370 K for Nb54Ru46 and 320 K for Ta54Ru46. These results mean that the transformation for V-Ru alloys is caused by the band Jahn-Teller effect, while the one for Nb-Ru and Ta-Ru alloys is mainly caused by the lattice interaction.
