Specific heat and resistivity of the GeTe-SnTe alloy system

The concentration-dependence of the room-temperature resistivity, the low-temperature electronic specific heat coefficient γ, and the Debye temperature θD of the Ge1−xSnxTe alloy system have been measured. Although θD drops linearly with increasing SnTe concentration, the behaviour of the resistivity and the electronic specific heat coefficient is unusual. In addition to the expected parabolic behaviour of the resistivity with composition (Nordheim's rule), a large extra contribution is also observed for the GeTe-rich alloys, while γ, after an abrupt drop for concentrations near GeTe, is then almost constant across the rest of the series. Using the theory developed by Dugdale and Guénault for the Pd-Ag alloy series and suitably adapting it to the GeTe-SnTe system, this behaviour can be completely described in terms of two independent scattering mechanisms, involving a common light-hole band and a partially occupied, high density of states, heavy-hole band associated only with GeTe.