Diffusion of transition metals (Co,Ni) and its effects on sol–gel derived ZrO2 polymorphic stabilities

Abstract

Transition-metal-incorporated ZrO₂ gel matrices have been prepared by an impregnation method. The polymorphic forms of the studied gels at room temperature were determined by Fourier-transform IR (FTIR) spectroscopy and X-ray diffraction (XRD) techniques, and the phase transformation behaviour of the gels was investigated with using differential thermal analysis (DTA) methods. For both undoped and doped ZrO₂ gels, DTA reveals metastable tetragonal–monoclinic–tetragonal–cubic phase transformations in the heating process up to 1400 °C. A high-temperature tetragonal–monoclinic transition is also observed in the cooling process. For the metal-loaded ZrO₂ gels, it is found that the diffusing metal cations stabilize the low-temperature tetragonal phase. However, for high-temperature (900 °C) calcined gels, both as-prepared and metal-stabilized tetragonal phases are reduced substantially. Correlations between metal diffusion and gel polymorphic stabilities are also demonstrated.