Thermal conductivity and stability of Al-doped ZnO nanostructured ceramics

Pure and Al-doped ZnO powders have been sintered by Spark Plasma Sintering. Al doping allows the ceramics to reach a relative density greater than 90% at a sintering temperature of 500 °C. The morphology of powder nanoparticles impacts the final grain size of the sintered bulk compounds. A ceramic sintered from isotropic nanoparticles of 30 nm in diameter can reach an average grain size of 110 nm, whereas a ceramic sintered from platelets and isotropic nanoparticles exhibits an average grain size in the submicrometric range. The influence of ceramic grain size on the thermal conductivity has been investigated. It shows that substantial decrease of the grain size from several microns down to 100 nm reduces the thermal conductivity from 29.5 to 7.8 W/m K at 100 °C. The stability of nanostructured ceramic has also been checked. After SPS, an annealing at 500 °C in air also leads to grain growth.