Magnetic Ni doping induced high power factor of Cu2GeSe3-based bulk materials

Abstract Cu2GeSe3 is an eco-friendly material, but pristine Cu2GeSe3 has poor thermoelectric properties. Here, the effects of magnetic Ni ion with unpaired 3d electrons on the electrical and thermal transport properties of Cu2GeSe3 are reported. Density functional theory (DFT) calculations indicate that the unpaired Ni 3d states cause the hybridization of Ni 3d orbitals with Se 4p orbitals near the Fermi level, giving rise to an increase in density of states (DOS). Combined with the significantly increased carrier concentration, a power factor (S2σ) value of ∼8.0 μWcm−1 K−2 at 723 K is achieved in Cu2Ge0.8Ni0.2Se3 sample, seeming to be the highest compared with the other Cu2GeSe3 systems. Meanwhile, the substitution of Ni for Ge causes the obvious local distortions in Cu2GeSe3 lattice, which yields the large strain fluctuations to suppress the lattice thermal conductivity. Consequently, a peak ZT value of ∼0.38 at 723 K is obtained in Cu2Ge0.9Ni0.1Se3 sample.