Hf/Sb co-doping induced a high thermoelectric performance of ZrNiSn: First-principles calculation

Abstract

Previous experiments showed that Hf/Sb co-doping in ZrNiSn impressively improved the electrical conductivity (σ). To explore the physical reasons for this improvement, the electronic structures of HfxZr1−xNiSn1−ySby (x = 0, 0.25, 0.5; y = 0, 0.02) have been systematically investigated by using the first-principles method and semiclassical Boltzmann transport theory. 50% Hf doping at Zr site in ZrNiSn simultaneously increases the degeneracy and dispersion of energy bands near the conduction band edge, which are helpful to optimizing Seebeck coefficient and slightly improving σ. Furthermore, 2% Sb co-doping at Sn site in Hf0.5Zr0.5NiSn not only increases total density of states near the Fermi energy but also retains high mobility, and N v reaches eleven at the conduction band minimum, thereby inducing a large improvement in σ. Additionally, the Bader charge analysis shows the reason why Sb co-doping supplies more electrons. It is most likely derived from that Sb loses more electrons and Sb-Ni has a stronger hybridization than Sn-Ni. Moreover, we predict that the ZT of Hf0.5Zr0.5NiSn0.98Sb0.02 at 1000 K can reach 1.37 with the carrier concentration of 7.56 × 1018 cm−3, indicating that Hf/Sb co-doping may be an effective approach in optimizing thermoelectric properties of ZrNiSn alloy compounds.

Band Structure Modification and Mass Fluctuation Effects of Isoelectronic Germanium-Doping on Thermoelectric Properties of ZrNiSn

“…Here, reduction in the experimental energy band gap as observed in Ge-doped ZrNiSn HH samples can be ascribed to the augmentation in the carrier concentration by thermally excited carriers and increased μ which jointly enhances σ. 56 The comparison of experimental band gap (see Table 3) and the theoretically calculated one using DFT (see Figure 4) exhibits contradictory behavior with doping of Ge, which may be an outcome of theoretical overestimation and synthesis defects inducing atomic disorders 38,58 as observed previously in HHs.…”

Thermoelectric Properties of Doped-Cu3SbSe4 Compounds: A First-Principles Insight

“…Further, the presence of hole (electron) pockets is favorable for achieving better TE properties, since more carriers would be allowed. The total number of hole (electron) pockets is determined by the number of VBM (CBM) in the Brillouin zone and the position of the Fermi level. , As seen in Figure , N v (number of degenerate valence bands) of Cu 3 SbSe 4 and Cu 3 Sb 1– x M x Se 4 at the Γ point on the top of VB is N v = 2. According to the relation between the effective masses and m DOS * ( m DOS * = N v 2/3 m* ), higher N v will increase m DOS * and S. Apart from the VBM at the Γ point, there is another valence band extremum (VBE) with little difference in energy that occurs at the M point.…”

“…The total number of hole (electron) pockets is determined by the number of VBM (CBM) in the Brillouin zone and the position of the Fermi level. 49,50 As seen in Figure 2, N 2) is ∼0.05 eV for the native compounds and those ones doped with isoelectronic elements (M = P, As, Bi). Meanwhile, this energy difference decreases up to 0.02 or 0.03 eV for Cu 3 SbSe 4 doped with IIIA or IVA group elements, respectively.…”

“…In addition, doped compounds with M = Al, Ga, In, Tl also present a VBE over the Fermi level along X-R direction, which would lead to an additional hole pocket. The presence of several hole pockets with almost equal energies is favorable for higher <x 50 3.2. Formation Energies.…”

Enhanced thermoelectric performance in Sb–Br codoped Bi2Se3 with complex electronic structure and chemical bond softening

“…Such a good band feature may be associated with excellent thermoelectric properties, as found in other thermoelectric materials. 39,41 To clearly understand the states near the E F , we calculate the total density of states (TDOS) for Bi 2 Se 3 , BiSbSe 3 , and BiSb(Se 0.92 Br 0.08 ) 3 respectively, as shown in Fig. 4(a).…”