Effect of Al co-doping on the phase transition of V-doped ZrO₂

Abstract

In this study, V-doped, Al-doped, (Al,V)-doped, and pure ZrO₂ powders were prepared using a complex polymerization method, and the thermally decomposed products were characterized using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). After calcination at 500 °C in air, several small broad peaks were observed in the XRD patterns of all samples. As the heating temperature increased, the phase-transition behavior of ZrO₂ varied among the four samples. The phase transition from tetragonal to monoclinic ZrO₂ was enhanced in ZrO₂ doped with V, but suppressed in ZrO₂ doped with Al. The tetragonal phase (t-ZrO₂) was dominant in the sample co-doped with Al and V and in Al-doped ZrO₂ samples calcined at 700 °C and below, and no diffraction peaks associated with the monoclinic phase (m-ZrO₂) were observed. However, after calcination at 800 °C, the diffraction peaks of t-ZrO₂ disappeared, and a single phase of m-ZrO₂ was observed. SEM observations revealed that the V-doped ZrO₂ particles were composed of fine particles in the range of 20–30 nm. In contrast, the SEM images of the (Al,V)-doped ZrO₂ powder indicated an increase in agglomerate size compared with that without Al doping. However, elemental analysis using energy-dispersive X-ray spectroscopy (EDX) showed no agglomeration or segregation of Al or V.