Amphoteric-Dopant Model Applied to Multiband Analysis of Electrical Transport Properties of n-Type PdxCu1−xFeS2 Including an Impurity Band.

The reported experimental data of the temperature dependence of the electrical conductivity, σ(T), the Seebeck coefficient, S(T), and the Hall coefficient, R_H(T) on n-type Pd_xCu_1−xFeS₂ (x = 0, 0.005, 0.01, and 0.02) polycrystalline samples have been analyzed including not only free-electron conduction in the 1st and the 2nd conduction band minimum (CBM) but also hopping conduction in an impurity band. The hopping mechanisms have been identified through the analysis of the reduced local activation energy of the conductivity. The amphoteric nature of Pd impurity atoms is assumed: a part of the doped Pd atoms are assumed to substitute the Cu-sites to form single donor states Pd_Cu, while the rest are assumed to substitute the Fe-sites to form compensating acceptor states Pd_Fe. Treating the density-of-states effective mass of the 1st CBM and the static dielectric constant as common fitting parameters, simultaneous fits to the σ(T), S(T), and R_H(T) data have been successfully performed. Through the fits, the concentrations of donors and acceptors together with the ionization energies of the donor levels have been deduced for each sample. It is revealed that the concentration ratio of Pd_Cu:Pd_Fe is about 1.5:1. [ABSTRACT FROM AUTHOR]