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

Abstract

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 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 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 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 CuCrO 2. The X-ray powder diffraction studies revealed the formation of 3R-CuCrO 2 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 Å and c = 17.0723 Å 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.

The efficiency of short sintering time on thermoelectric properties of delafossite CuCr0:85Mg0:15O2 ceramics

“…HRTEM micrographs of CuCr 0.85 Mg 0.15 O 2 compounds, as seen in Figure2was used as a supplemental tool for the X-ray diffraction method to detect the existence of the multi-phases in the compounds. The co-existence of CuCrO 2 , MgCr 2 2 phase can clearly be observed via the grains with the face like "terraces" because the delafossite material has the layer structure[23][24][25] . Besides, for the sample prepared with low dwell time, grains with the + and Cu 2+ ion states.Besides, the appearance of a broadband located at ca.…”