Crystal structure, chemical bond and enhanced performance of β-Zn₄Sb₃ compounds with interstitial indium dopant

Highlights: • The interstitial In dopant leads to the local structural perturbations in β-Zn₄Sb₃. • The simultaneous increases in α and σ are observed in the In-doped Zn₄Sb₃ compounds. • The In dopant plays different doping behaviors by the dopant contents in the samples. • A maximum ZT of 1.41 at 700 K is achieved for the In-doped Zn₄Sb₃ compounds. - Abstract: In-doped β-Zn₄Sb₃ compounds (Zn_4−xIn_xSb₃, 0 ⩽ x ⩽ 0.24) were prepared by melt-quenching and spark plasma sintering technology in the work. The resultant samples were systematically investigated by X-ray diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry and thermoelectric property measurements. The In dopant was identified to preferentially occupy the interstitial site in β-Zn₄Sb₃ and led to the local structural perturbations near the 12c Sb2 and 36f Zn1 sites. The Auger parameters of Zn and Sb indicated that the increase in the valence of Zn was attributed to the charge transfer from Zn to In atoms. The binding energies of In 3d_5/2 core level showed that the interstitial In dopant was n-type dopant (In³⁺) in slightly In-doped Zn_4−xIn_xSb₃, but acted as acceptor and was p-type dopant (In⁺) in heavily In-doped ones. The discovery provides a reasonable explanation for the puzzled relation between σ and x for Zn_4−xIn_xSb₃. Simultaneously increasing the electrical conductivity and Seebeck coefficient of Zn_4−xIn_xSb₃ can be realized through the local structural perturbations. The significantly enhanced power factor and the intrinsic low thermal conductivity resulted in a remarkable increase in the dimensionless figure of merit (ZT). The highest ZT reached 1.41 at 700 K for Zn_3.82In_0.18Sb₃ and increased by 68% compared with that of the undoped β-Zn₄Sb₃