Abstract
Semimetals have recently emerged at the forefront of contemporary thermoelectrics research. In this paper, we show that the candidate Dirac semimetal CaAgP forms with a stable CaAg0.9P composition. Intentionally, Ag-deficient CaAg0.9P shows a promising thermoelectric figure of merit, achieving zT = 0.43 at 660 K. This derives from moderate power factors, S2/ρ = 1.25 mW m−1 K−2, and a low lattice thermal conductivity, κlat = 1.2 W m−1 K−1. The thermoelectric properties of CaAg0.9P are consistent with that of a small bandgap semiconductor. High levels of doping are key to suppressing bipolar transport, enabling promising zT values, despite the low ∼0.2 eV bandgap. Unusually, the onset of bipolar transport coincides with a transition to a more electrically resistive state, indicating a fundamental change in electronic properties at high temperature.
Highlights
E Seebeck coefficient, q is the electrical resistivity, j is the sum of lattice, electronic, and bipolar thermal conductivities, and T is the absolute temperature
Thermoelectric materials research has traditionally focused on low bandgap semiconductors
Examples of novel thermoelectric behavior in semimetals include huge power factors S2/q > 100 mW mÀ1 KÀ2 and giant Peltier coefficients 100 A cmÀ1 KÀ1 at 10–15 K in Ta2PdSe6.8,9 Applied magnetic fields have been found to result in improved properties with S2/q $ 50 mW mÀ1 KÀ2 at 40 K and 9 T in TaP,10 and zT $ 1.1 at 350 K and 7 T in Cd2As3.11
Summary
E Seebeck coefficient, q is the electrical resistivity, j is the sum of lattice (jlat), electronic (jel), and bipolar (jbi) thermal conductivities, and T is the absolute temperature.3. The thermoelectric properties of CaAg0.9P are consistent with that of a small bandgap semiconductor.
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