The thermal conductivity of polycrystalline Al‐doped ZnO was controlled through the fabrication of nanostructured polycrystalline materials, by hot‐pressing nanosized Zn1–xAlxO (x= 0.01, 0.02) particles, which were synthesized by a coprecipitation and spray‐drying method. This process resulted in an improved thermoelectric power factor because of the nanosized Zn0.99Al0.01O particles of the polycrystalline products. The thermal conductivity also was decreased as a result of the formation of nanocrystalline Zn0.99Al0.01O.
Thermoelectric elements consisting of the layered polycrystalline materials of Al‐doped ZnO and NaCo2O4 were prepared using the pulse electric‐current sintering (PECS) method at 900°C for 3 min. Direct contact between the polycrystalline Al‐doped ZnO and the NaCo2O4 was obtained in a single‐step process for the stacked powders. The electrical conductivities of the polycrystalline materials prepared by PECS were higher than those of materials prepared by conventional sintering, despite their porous structure. The thermoelectric voltage of the 1‐mol%‐Al‐doped ZnO and NaCo2O4 polycrystalline element (measuring ∼6 mm × 3 mm × 15 mm) was 83 mV at dT= 500 K, when the junction of the elements was at 800°C.
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