Cubic‐Formation and Grain‐Growth Mechanisms in Tetragonal Zirconia Polycrystal

Abstract

The microstructure in Y 2 O 3 -stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°-1500°C was examined to clarify the role of Y 3؉ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y 2 O 3 concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grainboundary faces in Y-TZP and Y 3؉ ions segregated at their grain boundaries over a width of ϳ10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y 3؉ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y 3؉ ions segregating along the grain boundary, respectively.

Microstructure, crystallization and shape memory behavior of titania and yttria co-doped zirconia

“…By comparing the grain structure seen in the SEM image with the elemental maps, one can see that the yttrium segregation into LYR and HYR domains occurs in a grain-wise fashion. There is no clear suggestion of localization at grain boundaries as suggested by Schelling et al 13 Yttrium has a low solubility in the tetragonal zirconia crystal structure 13 , so the excess yttrium tends to accumulate in the cubic phase. The titanium distribution is rather homogeneous as compared to yttrium, which is expected as titanium solubility in tetragonal zirconia is higher than 5 mol%.…”

“…Typical powder processed Y-TZP generally has submicron grains as well as an inhomogeneous Y 2 O 3 distribution. 13 Since small grains tend to F o r P e e r R e v i e w 3 suppress the martensitic transformation, when such polycrystals are subjected to applied stress, cracks are generally initiated before achieving observable shape deformation via the transformation. On the other hand, in our recent work 14 , we showed that for small-volume samples with a length scale reduced to a few micrometers, zirconia ceramics will have an oligocrystalline structure and can exhibit significantly enhanced shape memory properties without cracking.…”

Enhanced reliability of yttria-stabilized zirconia for dental applications

“…To support this idea, the progressive development of a bimodal grain distribution can be appreciated from micrographs, which is often observed in Y-TZP after long sintering times or at higher temperatures [43]. Nonetheless, with these sintering conditions we are still far from the equilibrium and the conversion from tetragonal to cubic phase needs the formation of highly concentrated regions where the tetragonal distortion is reduced enough to nucleate the new phase [44]. Hence, the amount of cubic phase will be sensitive to the sintering time at this temperature [45,46].…”

Structure and Composition of Ba-W-Ti-O Ceramics Interface Regions Formed at Ultrasonic Vibration

“…The physical characteristics of barium-titanate ceramics were shown to be size dependent [1][2][3][4], and the Ba/Ti ratio was found to determine the grain growth mechanism [5,6]. At the same time, as was shown in [7][8][9], the relation between the elements in the ceramic interface regions may substantially differ from that in the bulk, which can result in both phase transformation and new phase formation. There may form, for example, a cubic-phase layer in the interface regions of polycrystalline tetragonal ceramics BaTiO 3 [10], a BaCO 3 phase as a result of interaction with atmospheric CO 2 on heating [11], and a glass phase in the interface areas of segnetoelectrical ceramics [12].…”