Anomalous Thermal Conductivity of Cd3As2 and the Cd3As2−Zn3As2 Alloys

The room-temperature lattice thermal conductivity of Zn3As2 is 0.012 W/cm·°C; that of Cd3As2 is 0.014 W/cm·°C or less. Anomalously low thermal conductivities (as much as 30% below calculated values) are found for samples of Cd3As2 and Cd-rich alloys of Cd3As2 with Zn3As2 where the electrical conductivity is high (103 Ω−1 cm−1). Thermal conductivities for Cd3As2 samples fall into two groups: Samples doped with an element which is expected to enter the anion sublattice have normal thermal conductivities, while undoped samples or those doped with an element which should enter the cation sublattice tend to have anomalously low thermal conductivities. High electron mobilities and general lack of correlation of carrier concentration with thermal conductivity indicate that the anomaly is not in the electronic component of thermal conductivity. Instead, doping experiments, as well as the temperature dependencies of thermal conductivities indicate that the anomaly is entirely in the lattice component and is due to a lattice defect in the anion sublattice, probably an As vacancy. Although the lattice thermal conductivity of some samples of Cd3As2 appears to be only 0.003–0.004 W/cm·°C, their electron mobility is 104 cm2/V·sec. To explain the apparently enormous phonon scattering cross-section of the lattice defect, it is suggested that the phonon scattering may involve the transitions of localized electrons from one type of As site (vacancy) to another (there are three different types of As sites in Cd3As2).