Miwa Saito

Reduction of thermal conductivity in dually doped ZnO by design of three-dimensional stacking faults

A design paradigm for fabrication of high quality thermoelectric material was demonstrated by using wurtzite ZnO based materials. To prepare the three-dimensional stacking faults in the microstructure of ZnO, Ga2O3 and In2O3 which were guided by atomistic simulation were selected as doping oxides in wurtzite ZnO. TEM microanalysis experimentally confirmed two kinds of stacking faults which were along the basal-plane (i.e. {0001}) and pyramidal-plane (i.e. {10–14}) in the microstructure of ZnO dually doped with small amount of Ga2O3 and In2O3. Also, EDS analysis results indicated the dopant segregation effect at stacking faults which was predicted by our atomistic simulation results. By varying doping levels, it was found that the (Ga0.004, In0.004)Zn0.992O with dense three-dimensional stacking faults revealed low lattice thermal conductivity (1.7 W m−1 K−1 at 773 K) and high thermo-electric performance (ZT: 0.19 at 773 K) in the present work. Based on all experimental results, it is expected that the combined method of atomistic simulation, microanalysis and processing route design will provide us great opportunity for design of three-dimensional stacking faults in the microstructure of ZnO with high performance.

Thermoelectric properties of p-type perovskite compounds LaCoO3 systems containing the A-site vacancy

Thermoelectric properties of Sr-doped LaCoO3 system which includes both La1−xSrxCoO3 and La0.95−xSrx0.05CoO3 containing the A-site vacancy were prepared by solid state reaction. The crystal phases of the samples were investigated by X-ray diffraction method. The electrical conductivity, Seebeck coefficient, and thermal conductivity were investigated, focusing the effect of A-site vacancy. Doping of Sr to LaCoO3 improved the electrical conductivity but decreased the seebeck coefficient and increased the thermal conductivity. A-site vacancy of La0.95−xSrx0.05CoO3 system, in comparison with La1−xSrxCoO3 system, increased electrical conductivity, and decreased lattice thermal conductivity. As a result, it was found that the thermoelectric properties of La0.95−xSrx0.05CoO3 containing the A-site vacancy showed the higher values than those of La1−xSrxCoO3. The introduction of A-site vacancy was effective on the improvement of thermoelectric property.