SURFACE CHARACTERIZATION OF YTTRIA-STABILIZED TETRAGONAL ZRO2 .1. STRUCTURAL, MORPHOLOGICAL, AND SURFACE HYDRATION FEATURES

The characterization of three microcrystalline Y2O3-stabilized tetragonal zirconia (t-ZrO2) preparations was carried out by BET, XRD, HRTEM, and FTIR spectroscopy, and revealed that morphological and surface features of t-ZrO2 specimens depend, much more than in the case of the monoclinic modification (m-ZrO2), on the preparative history of the material. Preparations fired at T less-than-or-equal-to 1000 K are mostly made up of coin-like particles terminating with the same crystal plane and present only one surface OH species, but after firing at higher temperatures crystal shape and morphology of the various preparations start changing appreciably and differing from one another. The morphological changes are also monitored by changes in the IR spectrum of the surface OH layer, which becomes quite similar to that of the microcrystalline m-ZrO2 phase. After firing at T greater-than-or-equal-to 1173 K, some of the t-ZrO2 preparations will generate to various extents (depending on the Y2O3 content and on the preparative procedure) an amorphous phase coating the particles. This modification can be monitored by appreciable changes in the IR spectrum of the surface OH layer.