Synthesis of CuAlO2 from chemically precipitated nano-sized precursors

A study was carried out on the synthesis of CuAlO2 at temperatures below 1000 °C, using a simple approach based on mechanical mixing of chemically precipitated CuO and Al(OH)3 nanoparticles. Synthesis of precursor powders was achieved at low temperatures (<100 °C) via precipitation from their corresponding aqueous solutions. After drying at room temperature, precursors were mixed in equimolar ratios by a combination of ball milling and sonication. Green pellets were obtained by filtration casting of the mixed powder slurry followed by dry compaction. X-ray diffraction study showed that the single phase CuAlO2 samples with high crystallinity formed only after 5 h of firing at 900 °C under flowing nitrogen. Electron microscopy images revealed a loosely packed microstructure with high surface area consisting of nanosized grains after the heat treatment. The achieved relative density was 45% of the theoretical density. The crystallite size was estimated to be 39 nm and the specific surface area of the sintered sample was measured as 9.67 m2/g. The bandgap was calculated as 3.07 eV with a transmittance of 60% in the visible region. The measured electrical conductivity was 4×10−3 mS/cm at room temperature and showed an increase with increasing measurement temperature, which indicates semiconducting behavior. The conductivity was shown to increase by an order of magnitude with a higher degree of densification by sintering at 1150 °C.