Transport and structural properties of binary skutterudite CoSb3 thin films grown by dc magnetron sputtering technique

Abstract

The results of the studies of structural, electrical, and thermoelectric properties of binary skutterudite CoSb3 thin films are presented. The n-type films were prepared without intentional doping on oxidized Si(100) and ceramic Al2O3 substrates using magnetron dc sputtering technique. The electron probe microanalysis has shown that the composition of the films is strongly affected by the preparation conditions. The x-ray measurements indicate the films to be amorphous if they are deposited on substrates kept at room temperature. On the basis of the differential thermal and x-ray analyses data, the temperature of the transition from the amorphous to crystalline state was established to be (153±1)°C. The films are polycrystalline with a preferential orientation of the growth along the (310) direction of the CoSb3 lattice if grown on substrates kept at 200 °C. The electrical resistivity ρ(T) and the Seebeck coefficient S(T) were measured from room temperature up to about 700 K. The value of ρ(T) decreases with increasing temperature. The maximum absolute value of the Seebeck coefficient is found to be −250 μV/K at around 550 K for both substrates. This is the highest value of the Seebeck coefficient for CoSb3 films deposited by dc magnetron sputtering. The predominant mechanisms of the scattering in CoSb3 are discussed on the basis of the temperature dependence of the Hall mobility. The carrier concentration n(T) is found to be around 1.2×1019 cm−3 at 300 K and is almost constant over the temperature range of (250–400) K. The room temperature measurements of the thermal conductivity carried out by the 3ω method have shown a value of about 3 W/(m K), which is significantly lower than that reported for bulk material.