Physical properties of thermoelectric zinc antimonide using first-principles calculations

Abstract

Abstract:We report first principles calculations of the structural, electronic, elastic and vibrational properties of the semiconducting orthorhombic ZnSb compound. We study also the intrinsic point defects in order to eventually improve the thermoelectric properties of this already very promising thermoelectric material.Concerning the electronic properties, in addition to the band structure, we show that the Zn (Sb) crystallographically equivalent atoms are not exactly equivalent from the electronic point of view. Lattice dynamics, elastic and thermodynamic properties are found to be in good agreement with the experiments and they confirm the non equivalency of the zinc and antimony atoms from the vibrational point of view. The calculated elastic properties show a relatively weak anisotropy and the hardest direction is the y direction. We observe the presence of low energy modes involving both Zn and Sb atoms at about 5-6 meV, similarly to what has been found in Zn 4 Sb 3 and we suggest that the interactions of these modes with acoustic phonons could explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the most stable defects and this explains the intrinsic p-type conductivity of ZnSb.

Review of Research on the Thermoelectric Material ZnSb

“…n-Type ZnSb is desired because (i) thermoelectric modules are preferably built of parallel legs of n-type and p-type materials, and it is preferable to use the same material (ZnSb) for minimizing the thermal stress; (ii) theoretically, n-type ZnSb is believed to be a much better thermoelectric material than p-type [36,40,42]. However, no real successful stable n-type doping has been achieved.…”

“…Schneider has reported an n-type to p-type transition in n-type Zn x Cd 1-x Sb every time when an oxygen gas was flushed into the sample container, and relaxed back to ntype after a certain time [71]. Another factor entering into explanations are Zn vacancies acting as acceptors and their migration [36,42,74]. A similar transition from n-type to p-type also occurs in the related compound CdSb, which has been attributed to Cd-vacancies [75].…”

“…The most favoured intrinsic defects in ZnSb are Zn vacancies, which are believed to yield ptype conduction [42,74]. The intrinsic defects in ZnSb have been calculated on by DFT methods [42,74]. The calculations gave much lower formation energies for Zn vacancies than other intrinsic defects, meaning that Zn vacancies will out-number other intrinsic defects by orders of magnitude.…”

“…This deviation is considered due to the intrinsic defects, giving a net hole concentration. The most favoured intrinsic defects in ZnSb are Zn vacancies, which are believed to yield ptype conduction [42,74]. The intrinsic defects in ZnSb have been calculated on by DFT methods [42,74].…”

“…The band structure of ZnSb has been calculated by ab-initio methods by many groups in recent years [2,26,31,[36][37][38][39][40][41][42]. The calculations are based upon density functional theory (DFT), but with varying detailed approximations and trade-offs between computational cost and accuracy.…”