Sub-micron-sized delafossite CuCrO$_2$ with different morphologies synthesized by nitratea€“citric acid sola€“gel route

摘要

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 CuCrO$_2$ was synthesized by sola€“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$^{circ}$C. At 750$^{circ}$C, the partial formation of delafossite CuCrO$_2$spheres with particle size in nano-regime was observed in the midst of platelets of spinel CuCr$_2$O$_4$. A green coloured powder with particle size 125a€“350 nm exhibiting distorted spheres was obtained at 775$^{circ}$C. The increase in temperature has a profound impact on the particle size, morphology and the optical properties of CuCrO$_2$. The X-ray powder diffraction studies revealed the formation of 3R-CuCrO$_2$ phase (rhombohedral, space group R-3m) as amajor product in the temperature range 775a€“1000$^{circ}$C. The unit cell parameters were found to be $a = b = 2.9711$ AA and $c = 17.0723$ AA at 1000$^{circ}$C. Scanning electron micrographs illustrated the different morphologies from spheres to hexagonal form via distorted spheres and cubes. The UVa€“Vis diffuse reflectance spectra measured for the powders exhibited semiconductor characteristics with an interesting size-related and temperature-dependent bandgap.