Low-temperature metastabilization of tetragonal V+4-containing ZrO2 solid solutions

The formation and characterization of tetragonal vanadium–zirconia solid solutions with different vanadium contents have been investigated. Vanadium–zirconia precursors were prepared by gelling mixtures of zirconium n-propoxide and vanadyl acetylacetonate, and studied over the range of temperature up to the tetragonal–monoclinic phase transformation. The formation of the tetragonal phase has been investigated by X-ray powder diffraction (XRD). It was found that it took place after annealing around 450°C for all specimens independently of the vanadium loading. In contrast, the temperature for the subsequent tetragonal to monoclinic transformation was dependent on the nominal vanadium content. Further characterization of the tetragonal–vanadium zirconia solid solutions by measurements of lattice parameters, ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy and electron paramagnetic resonance (EPR) revealed that vanadium was dissolved as V+4 replacing Zr+4 in octacoordinated sites in the crystal structure of tetragonal zirconia. The solubility limit of V+4 in tetragonal ZrO2 was about 5 mol% of vanadium. The EPR and diffuse reflectance spectroscopy results provided new evidence for the presence of V+4 in the tetragonal zirconia phase, which confirmed previous results in the V2O5–ZrO2–SiO2 ternary system.