UV Raman spectroscopic study on the surface phase of ZrO_2 modified with Nd_2O_3

摘要

The Nd_2O_3 modified ZrO_2 was synthesized using two methods of co-precipitation (Nd-ZrO_2) and wet impregnation (Nd/ZrO_2). The surface and bulk crystalline phases of Nd_2O_3 modified ZrO_2 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-ZrO_2 was not effectively stabilized by Nd_2O_3, as Nd_2O_3 is mainly present in the bulk of Nd-ZrO_2. However, in Nd/ZrO_2, it is found that with the impregnation of 0.5 mol% Nd_2O_3 on ZrO_2, the surface tetragonal phase of Nd/ZrO_2 can be stabilized even after calcination at 700 ℃ 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/ZrO_2. The formation of the aforementioned intermediate structure inhibits the phase transition from tetragonal to monoclinic in the surface region of Nd/ZrO_2. Furthermore, it is observed that the mixed tetragonal and monoclinic phases in the surface region of ZrO_2 which has been impregnated with Nd_2O_3 can also be stabilized after calcination at 700 ℃ This work provides a simple method for controlling the surface phase of ZrO_2 at high temperatures.