Sub-micron-sized delafossite CuCrO2 with different morphologies synthesized by nitrate–citric acid sol–gel route

Currently, copper chromium oxide crystallizing in delafossite structure attracts huge research interest due to its versatile applications arising from its layered structure. In this work, delafossite CuCrO2 was synthesized by sol–gel method from their respective hydrated nitrate salts with citric acid as a chelating agent. The phase formation temperature was found to be between 750 and 775∘C. At 750∘C, the partial formation of delafossite CuCrO2 spheres with particle size in nano-regime was observed in the midst of platelets of spinel CuCr2O4. A green coloured powder with particle size 125–350 nm exhibiting distorted spheres was obtained at 775∘C. The increase in temperature has a profound impact on the particle size, morphology and the optical properties of CuCrO2. The X-ray powder diffraction studies revealed the formation of 3R-CuCrO2 phase (rhombohedral, space group R-3m) as a major product in the temperature range 775–1000∘C. The unit cell parameters were found to be a = b = 2.9711 A and c = 17.0723 A at 1000∘C. Scanning electron micrographs illustrated the different morphologies from spheres to hexagonal form via distorted spheres and cubes. The UV–Vis diffuse reflectance spectra measured for the powders exhibited semiconductor characteristics with an interesting size-related and temperature-dependent bandgap.