Structural and Thermoelectric Properties of Polycrystalline p-Type Mg2−x Li x Si

Abstract

The aim of this study was to determine the location of Li atoms in Mg2Si structure, and verify the influence of Li dopant on the transport properties of obtained thermoelectric materials. The results of theoretical studies of the electronic band structure (full potential linearized augmented plane wave method) in Li-doped Mg2Si are presented. Theoretical calculations indicate that only in the case when Li is located in the Mg position, the samples will have p-type conduction. To confirm the theoretical predictions, a series of samples with nominal composition Mg2−xLixSi (x = 0–0.5) were prepared using the spark plasma sintering (SPS) method. Structural and phase composition analyses were carried out by x-ray and neutron powder diffraction, as well as scanning electron microscopy. Neutron diffraction studies confirmed that the lithium atoms substitute magnesium in the Mg2Si structure. The investigations of the influence of Li dopant on the transport properties, i.e. electrical conductivity, the Seebeck coefficient and the thermal conductivity, were carried out in a temperature range from 340 K to 720 K. Carrier concentration was measured with Hall method. The positive values of the Seebeck coefficient and Hall coefficient indicate that all examined samples show p-type conductivity. On the basis of the experimental data, the temperature dependencies of the thermoelectric figure of merit ZT were calculated.