Synthesis and magnetic properties of CuAlO2 from high-energy ball-milled Cu2O[sbnd]Al2O3 mixture

Abstract

Rapid synthesis of delafossite CuAlO2 using a mechanically activated mixture of microcrystalline Cu2O and nanocrystalline Al2O3 powder was achieved after subsequent annealing under argon atmosphere. The results were analyzed by using X-ray diffractometry, thermal analysis, transmission and scanning electron microscopy, Raman and X-ray photoelectron spectroscopy and SQUID magnetometry. The presence of core–shell configuration of Cu2O nanoparticles with the thickness of the non-crystalline surface shell of about 1.0 nm associated with partial oxidation of Cu2O was evident. By calcining the precursor in the temperature range of 300–800 °C for 4 h under Ar flow, CuO and CuAl2O4 were observed as main phases. At 900 °C, CuAlO2 became a main phase. At 1100 °C, CuAlO2 delafossite with a small admixture of α-Al2O3 was observed. Paramagnetism was observed on our CuAlO2 at room temperature with a weak ferromagnetism. In the 10 min activated mixture, a contamination with Fe was detected. A unique weak ferromagnetic feature of CuAlO2 may be associated with the structural paramagnetic Cu2+ and Fe3+ ions. Antiferromagnetic short-range-order was developed below 60 K. This was ascribed to the mixed state of Cu+ and Cu2+ in the CuO sub-lattice with a high amount of oxygen vacancies, similar to the states in the Cu2-xO.