Preparation of nano-powders of p-type transparent conductive copper aluminum oxide by co-precipitation method

Nano-powders of p-type transparent conductive copper aluminum oxide (CAO) have been successfully synthesized by co-precipitation method. By adding sodium hydroxide into the mixed solution of copper chloride and aluminum chloride, co-precipitate precursors of CAO with particle size around 50-60 nm were produced. After washing, filtering, and drying of the co-precipitates, nano-powders of CuAlO₂ were produced when the dried co-precipitate precursors were calcined at temperature above 1100°C. By aging at pH=3.5 for six hours and co-precipitating at pH=8.0, the atomic ratio of Cu/Al of the nano-powders can be maintained throughout the synthesis. After calcining at f 200°C in air for 4 hours, the CAO co-precipitate precursors totally transformed into nano-powders of CuAlO₂ with crystal size around 64 nm. Continued calcining at 1200°C above 4 hours led to the decomposition of CuAlO₂ into nano-powders of CuAl₂O₄ and volatile CuO with no significant change in crystal size. Finally, it was found that by calcining under inert atmosphere, the decomposition of CuAlO₂ could be suppressed at the expense of decreasing its crystallinity.