Structural study of holmium zirconate nanoparticles obtained through carbon neutral sol-gel process

The pyrochlore oxides are of potential interest as ion conducting electrolyte for intermediate temperature solid oxide fuel cell (SOFC). Nanopowders of holmium zirconate have been synthesised through ion-exchange between sodium alginate gel and metal complex solution followed by its thermal decomposition. Nanoparticles of Ho2Zr2O7 were obtained by calcining the dried gel beads at 700 °C for 2 h and 6 h duration respectively. An insight into calcination has been obtained employing simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). Thermal decomposition was also followed using High Temperature X-ray Diffraction (HTXRD) in static ambient atmosphere. Results from TGA/DSC and HTXRD corroborate with each other. Fine crystalline nanopowders of single phase Ho2Zr2O7 could be obtained after thermal decomposition at relatively low temperature (600–700 °C). Powder X-ray diffraction (XRD) revealed that the material has crystallized as single phase cubic Ho2Zr2O7 with defect fluorite structure. XRD and Raman spectroscopy were used to analyse the local structure of holmium zirconate. XRD scans of holmium zirconate and holmium hafnate prepared through identical method have been compared and the effect of cationic radius of Zr4+ and Hf4+ on B-site was studied. The crystallographic data obtained from XRD and transmission electron microscopy (TEM) are in good agreement with each other. This sol-gel method also referred as Leeds Alginate Process (LAP) is simple, cost effective, energy efficient and carbon neutral for the preparation of pyrochlore oxides (A2B2O7) solid electrolyte material for SOFC.