Electron paramagnetic resonance in combination with the thermal analysis, X-ray diffraction, and Raman spectroscopy to follow the structural properties of ZrxCe1-xO2 solid systems and precursors

The ZrxCe1-x(OH)(4) solids were prepared by simple precipitation of hydroxi des from known solutions of ZrOCl2. 8H(2)O and Ce(NO3)(3). 6H(2)O in aqueou s ammonium hydroxide. For x less than or equal to 0.5, the presence of a Ce O2 phase with a mixed Zr-Ce hydroxide has been evidenced by thermal analysi s and Raman and EPR spectroscopies. For this latter technique, the EPR sign al of Ce3+ ions was used as a probe to determine the presence of the CeO2 p hase. For x > 0.5, a pure ZrxCe1-x(OH)(4) was found without the formation o f the ZrO2 phase. After calcination under flow air at 700 degreesC of hydro xide samples, ZrxCe1-xO2 solid solutions were formed. For x less than or eq ual to 0.5, the solids possess a cubic phase slightly modified from that co rresponding to the pure CeO2 phase structure, since the Zr4+ ions replace i n the first step the Ce4+ ions located on the surface rather than in the bu lk of CeO2. For x > 0.5, the presence of Zr3+ ions corresponding to d(1) io ns in an octahedral environment with strong tetragonal distortion was evide nced. This ion was used as a probe to determine the phase nature of the Zrx Ce1-xO2 solid solution. This phase was attributed to a tetragonal one excep t for the pure ZrO2 solid, where a mixture of monoclinic and tetragonal pha ses was evidenced. As in the case of the XRD technique, EPR has been shown to efficiently evaluate the percentage of tetragonal or monoclinic phases i n the ZrO2 solid.