Chemical synthesis and characterization of Nb–ZrO2

Abstract

The effects of doping of ZrO with pentavalent ions have been insufficiently studied, given that some results indicate that doping does not suppress the monoclinic-tetragonal transformation of the material. To assess the influence of Nb and the calcination conditions on the morphology of ZrO2 in this study, ZrO2:Nb was prepared with dopant concentrations of 2.5mol%, 5.0mol% and 7.5mol%, and was microwave and conventionally calcined at temperatures of 500–1000°C. The XRD results revealed the presence of the orthorhombic, tetragonal and monoclinic phases of ZrO2 and the orthorhombic phase of Nb2Zr6O17. The Rietveld refinement indicated a volumetric fraction of more than 96% of the orthorhombic phase. Raman vibrational modes indicate the presence of tetragonal phase in all the samples and coexistence with other phases at higher temperatures. SEM micrographs of niobium-doped zirconia powders indicated the growth of particles with sizes varying from 1μm to 20μm, in response to increasing heat treatment temperatures and Nb content. The nitrogen adsorption–desorption isotherms of the sample revealed the presence of IV and V type isotherms characteristic of mesoporous materials. The average pore diameter distribution vs. incremental pore volume confirmed the existence of mesopores, whose average diameter was influenced by both dopant and temperature.