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 V
50+xRu
50−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 Nb
50+xRu
50−x and Ta
50+xRu
50−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 V
54Ru
46 is 7.5 mJ·mol
−1·K
−2, which is 4.2 times γ for Nb
54Ru
46 and 7.5 times γ for Ta
54Ru
46. The values of Debye temperature θ
D turn out to be 420 K for V
54Ru
46, 370 K for Nb
54Ru
46 and 320 K for Ta
54Ru
46. 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.
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