Papers by Keyword: ZT

Abstract: Successively forming GaSb islands by solid-phase epitaxy and covering them with a silicon layer, a nanostructured material containing 4 layers of GaSb nanocrystals (NCs) was grown on Si (111) surface. Due to a small size of the NCs (average height ~ 1.7 nm, average lateral size ~ 14 nm) and, as a consequence, to a significant quantum-size effect, a high electrical conductivity (~ 100 Ω^-1·cm^-1 at 600 K) together with a low thermal conductivity (~ 1 – 1.5 W·m^-1·K^-1 at 600 K) was obtained in the nanostructured material Si/NC_GaSb/Si. As a result, the thermoelectric figure of merit of the material has reached 0.82 at 600 K.

Abstract: In this study, we investigated a CuAl_0.9Fe_0.1O₂ compound prepared at two different sintering temperatures in order to find out the effect of sintering temperature on the compound's figure of merit of thermoelectric properties. The thermoelectric CuAl_0.9Fe_0.1O₂ compound was prepared from high purity grade Cu₂O, Al₂O₃ and Fe₂O₃ powders. The mixture of these powders were ground and then pressed with uniaxial pressure into pellets. The pellets obtained were sintered in the air at 1423 K and 1473 K. X-ray diffraction (XRD) patterns showed a single phase of CuAl_0.9Fe_0.1O₂ with rhombohedral structure, , along with a trace of CuO second phase. Moreover, the XRD peaks of the sample sintered at 1423 K indicated that more Fe³⁺ atoms replaced Al³⁺ atoms in this sample than they did in the sample sintered at 1473 K. The average grain size of the CuAl_0.9Fe_0.1O₂ compound prepared increased with increasing sintering temperature, whereas its mean pore size and porosity decreased with increasing sintering temperature. The dispersed small pores markedly decreased the thermal conductivity of the compound, while the Fe³⁺ substitution of Al³⁺ increased its electrical conductivity. The highest figure of merit (ZT) found was 0.021 at 973 K in the CuAl_0.9Fe_0.1O₂ sample sintered at 1423 K. Our findings show that this low-cost material with a reasonable figure of merit is a good candidate for thermoelectric applications at high-temperature.

Abstract: We report on the effect of Ni doping on the thermoelectric properties of p-type BiCuSeO oxyselenide, with layer structure composed of conductive (Cu₂Se₂)^2- layers alternately stacked with insulating (Bi₂O₂)²⁺ layers along c axis. After doping with Ni, enhanced electrical conductivity coupled with a moderate Seebeck coefficient leads to a power factor of ~231 μwm^-1K^-2 at 873 K. Coupled to low thermal conductivity, ZT at 873 K is increased from 0.35 for pristine BiCuSeO to 0.39 for Bi_0.95Ni_0.05CuSeO. However, the efficiency of Ni doping in the insulating (Bi₂O₂)²⁺ layer is low, and this doping only leads to a limited increase of the hole carriers concentration. Therefore Ni doped BiCuSeO has relatively low electrical conductivity which makes its thermoelectric figure of merit much lower than that of Ca, Sr, Ba and Pb doped BiCuSeO.