OxygenHole States in Zirconia Lattices: Quantitative Aspects of Their CathodoluminescenceEmission.

Systematic assessments of cathodoluminescence(CL) spectroscopy, Raman spectroscopy (RS), and X-ray diffraction(XRD) are presented for pure zirconia and for a series of Y-dopedzirconia powders (henceforth, simply referred to as undoped ZrO2and YSZ powders, respectively) synthesized according to acoprecipitation method of Zr and Y chlorides. Emphasis is placed hereon spectral emissions related to oxygen-vacancy sites (i.e., oxygenhole states) equally detected from undoped and Y-doped ZrO2samples, either as intrinsic defects or, extrinsically induced,by means of cathodoluminescence. Most counterintuitively, the undopedZrO2sample (i.e., the one with presumably the lowest amountof oxygen vacancies) experienced the strongest CL emission. A progressive“quenching” effect on CL emission with increasing thefraction of Y3+dopant could also be observed because theintrinsic vacancies present in the undoped lattice are the most efficientsince they can trap two electrons to gain electrical neutrality. However,as soon as Y3+ions are introduced in the system, thoseintrinsic vacancies migrate to Y-sites in next-nearest-neighbor locations,namely in a less efficient lattice location. This phenomenon is tentativelyreferred to as “delocalization” of vacancy sites. Moreover,the fact that Y-doped zirconia series presents quite similar CL spectracompared to the undoped zirconia could be an evidence that the radiativecenters of undoped and Y-doped ZrO2are basically the same.A fitting procedure has been made aiming to give a rational descriptionof the variation of the spectra morphology, and a parameter able todescribe the monoclinic to tetragonal phase transformation has beenfound. This parameter and the overall set of CL data enabled us toquantitatively assess polymorphic phase fractions by CL spectroscopyin the scanning electron microscope. [ABSTRACT FROM AUTHOR]