On anomalies of anisotropic thermal expansion near points of electronic topological transitions in noncubic metals. Applications to Zn, Cd and CdMg alloys

Abstract

Singularities of the low-temperature coefficients of the thermal expansion, α i ( T), near points of electronic topological transitions (ETT) in noncubic metals are investigated. Using a uniaxial metal with a weak pseudopotential of the electron-ion interaction as an example, it is shown that the longitudinal α ∥ and transverse α ⊥ coefficients should be opposite in sign near the ETT point, while the ∥α i ∥ values can considerably exceed the volume coefficient β= α ∥ + 2 α ⊥. These conclusions are illustrated by ab initio band structure calculations for the hcp Zn, Cd and CdMg alloys. The results explain the scale and sign of the α i low-temperature anomalies in Zn and Cd ( α ∥ > 0, α ⊥ < 0>). For the Cd 1- x Mg x alloys the anomaly inversion ( α ∥ < 0, α ⊥ > 0) is predicted after the first ETT at the point x= x c1 ≈0.06, as well as its sharp growth (the ∥α i ∥ increase) after the second ETT at x c2≈0.12.