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J. Japan Inst. Metals, Vol. 53, No. 3 (1989),

pp. 253-257

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

**
Takehiko Tsukamoto**^{1}, Kuniyuki Koyama^{2}, Akio Oota^{3} and Seiichiro Noguchi^{3}

^{1}Graduate Student, Toyohashi University of Technology, Toyohashi

^{2}Technology Development Center, Toyohashi University of Technology, Toyohashi

^{3}Department 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 T_{L} decreases with decreasing Ru concentration. The values of T_{L} 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 T_{L} values are not expressed as universal functions of Z. The Hall coefficient R_{H} for V_{50+x}Ru_{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+x}Ru_{50-x} and Ta_{50+x}Ru_{50-x} alloys, on the contrary, the R_{H} decreases monotonically with increasing x, showing no peak at the boundary composition. The value of electronic specific-heat coefficient γ for V_{54}Ru_{46} is 7.5 mJ•mol^{-1}•K^{-2}, which is 4.2 times γ for Nb_{54}Ru_{46} and 7.5 times γ for Ta_{54}Ru_{46}. The values of Debye temperature θ _{D} turn out to be 420 K for V_{54}Ru_{46}, 370 K for Nb_{54}Ru_{46} and 320 K for Ta_{54}Ru_{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.

(Received 1988/8/13)

#### Keywords:

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

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