Valence charge density of multi-doped Mg2Si thermoelectric materials from maximum entropy method analysis

The valence electron topologies of Mg2Si thermoelectric materials multi-doped with Al, Zn and Sb have been determined by the Maximum Entropy Method (MEM) using synchrotron X-ray powder diffraction data. In spite of the very low concentrations, expansion was observed in the cubic unit cells of the doped samples. Using pure Mg2Si as a reference, charge density difference maps revealed qualitative features on the distributions of the electrons contributed by the doped atoms. The presence of excess electrons shows all doped samples are n-type semiconductors and they are shared among the atomic sites. We evaluated the reliability of the MEM calculated charge density by considering the effect of successively increasing the number of high angle Bragg reflections used in the analysis on the diffraction pattern of a single doped Al-Mg2Si sample.