日本金属学会誌

J. Japan Inst. Metals, Vol. 53, No. 3 (1989),
pp. 253-257

Study of Structural Transformation in Near-Equiatomic M-Ru (M=V, Nb, Ta) Alloys Based on the Electron Theory

Takehiko Tsukamoto1, Kuniyuki Koyama2, Akio Oota3 and Seiichiro Noguchi3

1Graduate Student, Toyohashi University of Technology, Toyohashi
2Technology Development Center, Toyohashi University of Technology, Toyohashi
3Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi

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 θ D 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.


(Received 1988/8/13)

Keywords:

CsCl structure, cubic to tetragonal transformation, electrical resistivity, Hall coefficient, specific heat


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