Observation of Anomalously High Seebeck Coefficients in the Family of Zintl Phase Semiconductors Ca10RECdSb9 (RE = Rare-Earth Metal)

This work reports the synthesis, structure, and thermoelectric transport properties of the hole-dominated semiconductors with a general formula Ca10RECdSb9 (RE = Y, Ce, Nd, Sm, and Lu). These materials feature unexpectedly high Seebeck coefficients, up to 650 μV/K at 600 K, and electrical resistivities on the order of 1–1000 mΩ·cm, which is an indication of a degenerate semiconducting state. For example, the Seebeck coefficient observed in Ca10NdCdSb9 (309 μV/K at 600 K) is accompanied by low and metallic-like electrical resistivity (6 mΩ·cm) and a carrier concentration of n = 4.68 × 1020 cm–3. The calculated power factor PF in Ca10NdCdSb9 is 0.88 μW/cm·K2 at 300 K, and calculations based on the single parabolic band model indicate that an optimum PFopt of 1.68 μW/cm·K2 can be achieved at that temperature for a carrier concentration of nopt = 6.62 × 1019 cm–3. The estimated thermoelectric figure of merit zT in this material when properly tuned is expected to surpass zT = 1 at 600 K.