Ta对C—15相V2Hf和V2(Zr0.5Hf0.5)系列声子性能的影响

本文用中子飞行时间方法对C-15相的超导材料V₂Hf,V₂Ta和V₂Hf_0.8Ta_0.2以及V₂Zr_0.5。Hf_0.5和V₂Zr_0.5Hf_0.33Ta_0.17的热中子非弹性散射谱作了测量,并计算出相对的广义声子态密度。结果与早先发表的Nb对C-15相V₂Zr和V₂(Hf_0.5Zr_0.5)系列声子性能的影响一致:声子频率随超导转变温度T_c增加而软化,随T_c减小而硬化。这表明,对于此类材料弹性软化在一定程度上对提高T_c起了作用。结果还进一步表明V₂Zr或V₂Hf与V₂(Zr_0.5Hf_0.5)之间有着质的差别,V₂Hf加Ta后,T_c增加,声子频率软化,而V₂(Zr_0.5Hf_0.5)加Ta后,T_c减小,声子频率则略有硬化。这与V₂Zr和V₂(Hf_0.5Zr_0.5)加Nb的结果是一致的。此结果可以用角动量分波表象的能带论方法分析电-声耦合相互作用得出的杂化理论来定性解释。关键词：

THE EFFECT OF Ta ON BEHAVIOR OF PHONONS IN SUPERCONDUCTORS C-15 V2 Hf AND V2(Zr0.5Hf0.5)

Inelastic neutron scattering spectra from C-15 phase superconducting alloys V₂Hf, V₂Ta, V₂Hf_0.8 Ta_0.2, V₂Zr_0.5 Hf_0.5 and V₂Zr_0.5 Hf_0.33 Ta_0.17 were measured by the neutron time-of-flight method, and their relative phonon densities of states were evaluated. The present results show that the phonon frequencies soften with the increase of the superconducting transition temperature T_c and harden with the decrease of the T_c, which is in agreement with our previous results of "The effect of Nb on phonons of superconductors C-15 V₂Zr and V₂(Zr_0.5 Hf_0.5)". This means that for these superconductors the elastic softening plays a role in enhancing T_c to some extent. It seems that between V₂Zr or V₂Hf and V₂(Zr_0.5 Hf_0.5) there exists essential difference, which makes T_c increasing and the phonon frequencies softening for the formers while T_c decreasing and the phonon frequencies slightly hardening for the later after adding small amounts of Nb or Ta. It can be considered as the result of hybridzation of conduction bands, which is studied by means of the LMTO (linear combination of muffin-tin orbitals)method.