Abstract
In this paper, Cd 1 - x Sr x O polycrystalline bulks were synthesized via conventional solid state reaction method and the effect of Sr doping on the high temperature thermoelectric performance of CdO were investigated. XRD results revealed all samples were pure CdO and the lattice parameters increased with Sr content, demonstrating that all doped Sr entered the CdO lattice. The dopant Sr inhibited the grain growth of CdO polycrystals, gave rise to the reduction of grain size as well as increase of grain boundaries. Due to the large difference on electrical affinities of CdO and SrO, the introduction of SrO into CdO polycrystals resulted in decreased carrier concentration, which further led to the increment of both electrical resistivity and Seebeck coefficient. Experimental data on thermal properties verified that doping of Sr was an effective way to reduce the thermal conductivity of CdO. Attributing to the increased electrical resistivity, the electrical thermal conductivity decreased significantly with increasing Sr content. On the other hand, the long-wavelength phonon scattering was greatly enhanced by increased grain boundaries, resulted in suppressed phonon thermal conductivity. Meanwhile, the size and mass differences on Sr and Cd atoms led to strong strain field fluctuation scattering and mass fluctuation scattering, which drastically reduced the phonon thermal conductivity. Benefiting from the decreased electrical and phonon thermal conductivities, the total thermal conductivity experienced a remarkable reduction, from 3.52 W m -1 K -1 for the pristine CdO to 1.71 W m -1 K -1 for the Cd 0.95 Sr 0.05 O at 1000 K, lower than most oxide thermoelectric materials. Originating from the reduced thermal conductivity, the thermoelectric performances of all doped samples were promoted, the Cd 0.97 Sr 0.03 O sample reached the highest ZT value of 0.40 at 1000 K despite of the low power factor, which was 25% higher compared to pure CdO, and was comparable to the best reported n type oxide thermoelectric materials.
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