High-performance non-Fermi-liquid metallic thermoelectric materials

Searching for high-performance thermoelectric (TE) materials in the paradigm of narrow-bandgap semiconductors is hampered by a bottleneck. Here we report on the discovery of metallic compounds, TiFexCu2x−1Sb and TiFe1.33Sb, showing the thermopower exceeding many TE semiconductors and the dimensionless figure of merits zTs comparable with the state-of-the-art TE materials. A quasi-linear temperature (T) dependent electrical resistivity in 2–700 K and the logarithmic T-dependent electronic specific heat at low temperature coexist with the high thermopower, highlighting the strong intercoupling of the non-Fermi-liquid (NFL) quantum critical behavior of electrons with TE transports. Electronic structure analysis reveals a competition between the antiferromagnetic (AFM) ordering and Kondo-like spin compensation as well as a parallel two-channel Kondo effect. The T-dependent magnetic susceptibility agrees with the quantum critical scenario of strong local correlation. Our work demonstrates the correlation among high TE performance, NFL quantum criticality, and magnetic fluctuation, which opens up directions for future research.