New Zintl Phase Yb₁₀MgSb₉ with High Thermoelectric Performance

Abstract

Yb10MgSb9 is a new Zintl compound (with a composition closer to Yb10.5MgSb9) and a promising thermoelectric material first reported in this work. Undoped Yb10MgSb9 has an ultralow thermal conductivity due to crystallographic complexity and exhibits a relatively high peak p‐type Seebeck coefficient and high electrical resistivity. This is consistent with Zintl counting and density functional theory (DFT) calculations that the composition Yb10.5MgSb9 should be a semiconductor. Na is found experimentally to be an effective p‐type dopant potentially due to the replacement of Na+ for Yb2+, allowing for a significant decrease in electrical resistivity. With doping, a dramatic improvement of electrical conductivity is observed and the glass‐like thermal conductivity remains low, allowing for a significant enhancement of the thermoelectric figure of merit, zT. Doping increases the zT from 0.23 in undoped Yb10MgSb9 to 1.06 in 7 at% Na‐doped Yb10MgSb9 at 873K. This high thermoelectric performance found through Na‐doping places this material amongst the leading p‐type Zintl thermoelectrics, making it a promising candidate for future studies and high‐temperature thermoelectric applications.

Anion Redox Balances Valence against Compositional Fluctuations in the 10-1-9 Zintl Family

“…Trends in the experimentally measured thermoelectric properties of Yb 10.5– x Na x MgSb 9 can in part be explained by the counter-doping mechanism. While the addition of Na dramatically improves the thermoelectric performance (largely due to a reduction in electrical resistivity), the Seebeck coefficient changes very little with the addition of Na (Figure ).…”

“…Yb 10.5 MgSb 9 is a variation on Ca 10 LiMgSb 9 with Yb substituting on all of the Ca sites and with half occupancy on the Li sites (Figure 1b). 12 Note that the anion frameworks in the two compounds are identical.…”

“…The energy cutoff was set to 340 eV, and a Γ-centered k -point grid of density 4 × 4 × 2 was used to integrate over the Brillouin zone. Band structures were calculated along the standard high-symmetry k -point paths. , An experimentally refined structure of Yb 10.5 MgSb 9 was considered. Due to partial occupancies of the Yb sites, possible configurations of Yb orderings in the 10.5-1-9 stoichiometry were enumerated, and the lowest-energy structure was used.…”

“…11 Recently, the Mg analogue was discovered and demonstrated the highest zT among 10-1-9 materials through the addition of Na. 12 Thus, so far, this "10-1-9" Zintl antimonide structure has been reported for a variety of refined compositions which are compiled in Table 1. These reported materials are all considered to be disordered variations of the Ca 10 LiMgSb 9 material (Figure 1a), with a tetragonal crystal structure (space group: P4 2 /mnm) and lattice constants in the range of a = 11.8−11.9 Å and c = 16.9−17.3 Å.…”

“…The compound was later reported to be a decent thermoelectric . Recently, the Mg analogue was discovered and demonstrated the highest zT among 10-1-9 materials through the addition of Na …”