Anomalous Thermoelectric Performance in Asymmetric Dirac Semimetal BaAgBi

Abstract

Multiple-band degeneracy has been widely recognized to be beneficial for high thermoelectric performance. Here, we discover that the p-type Dirac bands with lower degeneracy synergistically produce a higher Seebeck coefficient and electrical conductivity in topological semimetal BaAgBi. The anomalous transport phenomenon intrinsically originated from the asymmetric electronic structures: (i) complete p-type Dirac bands near the Fermi level facilitate high and strong energy-dependent hole relaxation time; (ii) the presence of additional parabolic conduction valleys allows for a large density of states to accept scattered electrons, leading to an enlarged hole–electron relaxation time ratio and, thus, weakened bipolar effect. In combination with the strong lattice anharmonicity, an exceptional p-type average ZT of 0.42 is achieved from 300 to 600 K, which can be dramatically enhanced to 1.38 via breaking the C 3v symmetry. This work uncovers the underlying mechanisms governing the abnormal transport behavior in Dirac semimetal BaAgBi and highlights the asymmetric electronic structures as target features to discover/design high-performance thermoelectric materials.

Effects of Ti Doping on TaFeSb Half‐Heuslers Estimated by a Single Parabolic Band Model

“…Firstprinciples calculations based on the density functional theory and high-throughput calculations are further required to investigate the possible band convergence. [23,24] Equally, this also means that the peak PF of x = 0.16 is much greater than that of x = 0. Figure 4(b) shows the PF calculated using the μ W from Figure 4(a) (in lines).…”

“…(c) μ W estimated as a function of x using the simple equation from Snyder et al . at 970 K [23] . (d) Experimental PF as a function of x at 970 K from Ref.…”

“…Because the μ W can also be used as an indicator of the possible band convergence, the maximum μ W at x =0.12 may suggest the possible band convergence at x =0.12. First‐principles calculations based on the density functional theory and high‐throughput calculations are further required to investigate the possible band convergence [23,24] . Equally, this also means that the peak PF of x =0.16 is much greater than that of x =0.…”

“…Figure presents the peak Power Factor (PF) and peak zT of Ti-doped TaFeSb estimated using the SPB model. Figure 4(a) shows the weighted mobility (μ W ) calculated for different x in [23] (d) Experimental PF as a function of x at 970 K from Ref. [17].…”

“…[17]) and calculated Power Factor (PF) of Ta 1-x Ti x FeSb as a function of n H . (c) μ W estimated as a function of x using the simple equation from Snyder et al at 970 K [23]. (d) Experimental PF as a function of x at 970 K from Ref [17]…”