Remarkably High Thermoelectric Efficiencies of the Half-Heusler Compounds BXGa (X = Be, Mg, and Ca)

Abstract

The thermoelectric materials with high values of the dimensionless figure of merit (ZT) are among the most important new energy resources. Too much attention has been paid to the search of high-ZT thermoelectric materials, and the one with ZT = 5 has been reported recently. Here, a remarkably high ZT = 7.38 is predicted for the n-type half-Heusler compound of BCaGa at 700 K. To understand the high-ZT behavior, we studied electronic properties of BXGa (X = Be, Mg, and Ca) with first-principles calculations based on the density functional theory. The stabilities of the structures of BXGa (X = Be, Mg, and Ca) are confirmed by phonon dispersion. The transport properties are determined by the semiclassical Boltzmann transport theory. We evaluate the relaxation time by using the deformation potential theory and the lattice thermal conductivity based on the elastic coefficients. The results demonstrate that such a high efficiency of BCaGa arises from the intrinsic coordination of the ultralow lattice and electronic thermal conductivity and the larger power factor at certain carrier concentration and temperature. The high n-type power factor originates from the large relaxation time, which results in a light, twofold degenerate conduction-band pocket at the Γ point. In contrast, the power factors of BBeGa and BMgGa are smaller because of their flat-and-dispersive valence band. It is expected that the remarkable results for BXGa could encourage more experimental and theoretical investigations to develop efficient thermoelectric materials with BXGa.

Establishing the carrier scattering phase diagram for ZrNiSn-based half-Heusler thermoelectric materials

“…The temperature and carrier concentration dependences of the scattering provide possibilities for the manipulation of the transport properties. Therefore, mapping of a carrier scattering phase diagram in the space of temperature and carrier concentration would provide a useful guidance for optimization or design of TE materials, such as the study of BXGa (X = Be, Mg, and Ga) compounds 32 .…”

Remarkable High Thermoelectric Conversion Efficiency Materials of BeMF3 (M = Al, Y)

“…Compared with the two compounds, the τ s of BeYF 3 is greater than those of BeAlF 3 at the same temperature, which will influence the electrical conductivity and electronic thermal conductivity as well as the other transport coefficients, and finally impact the ZT values. Compared with other thermoelectric materials, the 143 fs of the electron τ for BeYF 3 is greater than those of the reported thermoelectric materials, such as 37.52 fs of RuTaSb, [ 46 ] although smaller than 462 fs of AgKTe, [ 35 ] 2063 fs of LaPtSb [ 43 ] and 2511 fs of BCaGa; [ 20 ] which suggests that BeYF 3 possesses moderate relaxation time but BeAlF 3 has smaller ones.…”

“…It should be noted that the presently largest S 2 σ of 0.016 W m −1 K −2 for the n‐type BeYF 3 is not large in comparison with the many ones in the literature, such as 0.43 W m −1 K −2 of LaPtSb, [ 43 ] and 0.47 W m −1 K −2 of BCaGa. [ 20 ] However, the ZT of BeYF 3 is in turn larger, which suggests a preferable thermoelectric performance is determined by the complex interaction of the physical quantities in Equation (2), as described in the introduction.…”

“…Ali et al. [ 18 ] found the p‐type power factor of KCaF 3 is larger at the properly charge carries, which lead the ZT of 0.7 at 800 K. Many other thermoelectric materials with higher ZT (>2) have also been reported, such as the full‐Heusler materials Ba 2 BiAu( ZT max = 5), [ 19 ] the half‐Heusler compound BCaGa( ZT max = 7.38), [ 20 ] the oxide monolayer La 2 Ti 2 O 7 ( ZT max = 2.5), [ 21 ] the monolayer SnSe and SnTe compounds( ZT max = 2.3 and 3.27), [ 22,23 ] ternary sulfur compound AgBi 3 S 5 ( ZT max = 2.24). [ 24 ]…”

Lattice thermal conductivity of half-Heuslers with density functional theory and machine learning: Enhancing predictivity by active sampling with principal component analysis

“…1, the XZ sublattice forms a rocksalt structure, while the Y Z sublattice forms a zinc-blende structure [27][28][29]. Several HH compounds have a high power factor in combination with relatively low κ , making HHs attractive for TE applications [8,13,[30][31][32][33][34][35][36]. Recently, Feng et al [37] used DFT-based calculations to show that the four HH compounds: CdPNa, BaBiK, LaRhTe, and LaPtSb have very low κ .…”