The transport properties of the cubic alkaline earths Ca, Sr, and Ba

Abstract

The electrical resistivity (ρ), thermoelectric power(S), and thermal conductivity (κ) of two Sr samples and two Ba samples have been determined from 30 to 300 K. Large deviations from Matthiessen's rule (DMR) were observed. The estimated transport properties for ideally pure Sr and Ba indicate that these elements, like Ca, show large deviations from the Bloch–Gruneisen form for ρ(T) at all temperatures, large and positive diffusion thermopowers with a negative phonon-drag contribution, and large deviations from the Wiedemann–Franz relationship (DWFR). In these respects, they are much more like the transition metals than the monovalent metals.In the second, analytical, portion of the paper we study the DWFR in some detail. First, the effect of lattice conduction is estimated, and found to be large. Then, a function X(E) of the electron energy, closely related to the conventional conductivity function σ(E), is estimated from the ρ and S data now available for Ca, Sr, and Ba above 300 K, and used to compute S and the Lorenz function for elastic electron–phonon scattering below 300 K. Comparison with the experimental data indicates that the energy dependence of the electron parameters is responsible for the electronic DWFR, and effects the diffusion thermoelectric power. Such 'band effects' may also be seen in the thermal resistivity due to inelastic scattering in at least Sr. Regrettably, we are not able to explain the observed DMR.