Promising thermoelectric performance in CaAgP with intrinsic Ag vacancies

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 CaAg_0.9P composition. Intentionally, Ag-deficient CaAg_0.9P 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, κ_lat = 1.2 W m^-1 K^-1. The thermoelectric properties of CaAg_0.9P 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.