UV Raman spectroscopic study on the surface phase of ZrO2 modified with Nd2O3

The Nd2O3 modified ZrO2 was synthesized using two methods of co-precipitation (Nd-ZrO2) and wet impregnation (Nd/ZrO2). The surface and bulk crystalline phases of Nd2O3 modified ZrO2 were investigated by using UV Raman spectroscopy, visible Raman spectroscopy, and X-ray diffraction (XRD). It is observed that the tetragonal phase in the surface region of Nd-ZrO2 was not effectively stabilized by Nd2O3, as Nd2O3 is mainly present in the bulk of Nd-ZrO2. However, in Nd/ZrO2, it is found that with the impregnation of 0.5 mol% Nd2O3 on ZrO2, the surface tetragonal phase of Nd/ZrO2 can be stabilized even after calcination at 700 °C. The UV Raman results indicate that a disordered structure, or intermediate structure, which is involved in the transition from the tetragonal to the cubic phase, is formed at the surface region of Nd/ZrO2. The formation of the aforementioned intermediate structure inhibits the phase transition from tetragonal to monoclinic in the surface region of Nd/ZrO2. Furthermore, it is observed that the mixed tetragonal and monoclinic phases in the surface region of ZrO2 which has been impregnated with Nd2O3 can also be stabilized after calcination at 700 °C. This work provides a simple method for controlling the surface phase of ZrO2 at high temperatures.