Zirconia tetragonal crystal

For instance, dislocations have been shown to play a key role in the accommodation process in YTZP, justifying the threshold stress in YTZP, in contrast with the hypothesis that this threshold stress is due to the electric field created by impurity segregation. However, dislocations are not systematically observed in YTZP furthermore it was shown that in yttria-stabilized tetragonal zirconia single crystals, the stress necessary to activate dislocations at 1400°C was over 400 MPa, one order of magnitude higher than the stresses used during superplastic deformation of YTZP at the same temperature. It will be necessary to conduct a systematic study of the microstructure of the monolithic ceramics such as YTZP before and after deformation and to correlate their relationship with the superplastic features. 

Mimurada, J., Nakano, M., Sasaki, K., Ykuhara, Y., and Sakuma, T., Effect of cation doping on the superplastic flow in yttria-stabilized tetragonal zirconia poly crystals , J. Am. Ceram. Soc, 2001, 84, 1817-21. 

Y-TZP Yttria-stabilized tetragonal zirconia poly crystals... 

N. Bonanos and E. P. Butler [1985] Ionic Conductivity of Monoclinic and Tetragonal Yttiia-Zirconia Single Crystals, /. Mat. Sci. Lett. 4, 561-564. 

Therefore, samples possess higher surface areas and pore volumes and smaller crystallite domains (Chap. 21) than samples prepared by precipitation even after calcination at relatively high temperature of 500°C. Note that zirconia aerogels are typically stabilized in their tetragonal crystal phase, so that they maintain this crystallographic structure, even after calcination at temperatures as high as 700°C (Chap. 23). Conventional mesoporous samples are converted from tetragraral to monoclinic under similar calcination treatment... 

Tetragonal structure, of ferroelectric crystals, 11 95, 96 Tetragonal symmetry, 8 114t Tetragonal zirconia polycrystals, 5 571 Tetrahedral... 

On heating to 1500 °C/6 h/Ar, the Zr material crystallizes to a mixture of monoclinic and tetragonal zirconia and crystobalite with loss of considerable original surface area (36 m2 g 1). The Hf material behaves similarly, although it partially crystallizes at 1000 °C to produce cubic or tetragonal hafnia. Cristobalite is only observed in materials heated to 1400 °C. Finally, thin films of the Zr and Hf derivatives could be cast from hydrocarbon solutions on quartz and then converted to thin films of the corresponding amorphous or ceramic materials. 

Superacid sites are not created by impregnation on the crystallized oxides, but on the amorphous forms whose calcination then converts them to the crystalline forms. Recent work shows that a W03/Zr02 catalyst prepared by impregnation of the crystalUne zirconia (65% tetragonal, 35% monocUnic) exhibits comparable behavior [77, 78]. 

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