XANES and EXAFS study of the local order in nanocrystalline yttria-stabilized zirconia (original) (raw)
Related papers
Short-range order of yttria doped zirconia powders studied by X-ray absorption (II)
Journal of Alloys and Compounds, 1996
The atomic structure of polymorphic zirconia powders doped with 6 mol.% yttria prepared by controlled hydrolysis of alkoxides has been studied by X-ray absorption spectroscopy. The short-range orders before and after heat treatment have been compared. The crystallization and incorporation of the yttrium atoms into the network have been monitored. Rietveld analysis of X-ray diffraction data has been used to determine the relative amounts of crystalline phases present in the sample.
Structure of nanocrystalline zirvonia and yttria
Nanostructured Materials, 1995
A combination of spectroscopic and imaging methods was chosen to investigate extended (XRD, TEM) and local (EXAFS, HR-TEM) structure of nanosized ZrO2 and Y2O3. Phase content of the powders was determined by Rietveld analysis. We investigated phase stability of metastable polymorphs in n-oxides by in-situ high temperature and high pressure XRD. EXAFS oscillations in nano oxide powders (5 to 30 nm) are distinctly weaker compared to coarse grained samples. In a compacted and sintered sample of n-Zr02 (80 nm) the EXAFS oscillation is nearly identical to the monoclinic coarse grained powder. High-Resolution-TEM micrographs show crystalline grains with grain sizes between 5 and 30 nm. Image contrast simulations of n-ZrO, powder micrographs indicate at least for some particles a shell like structure with different ph.ases.
Crystal structure and local order of nanocrystalline zirconia-based solid solitions
Powder Diffraction, 2008
Crystal and local structures ͑longand short-range order, respectively͒ of four nanocrystalline zirconia-based solid solutions-ZrO 2-6 and 16 mol % CaO and ZrO 2-2.8 and 12 mol % Y 2 O 3-synthesized by a pH-controlled nitrate-glycine gel-combustion process were studied. These materials were characterized by synchrotron X-ray diffraction ͑XRD͒ and extended X-ray absorption fine structure ͑EXAFS͒ spectroscopy. Our XRD results indicate that the solid solution with low CaO and Y 2 O 3 contents ͑6 and 2.8 mol %, respectively͒ exhibit a tetragonal crystallographic lattice, and those with higher CaO and Y 2 O 3 contents ͑16 and 12 mol %, respectively͒ have a cubic lattice. Moreover, our EXAFS study demonstrates that the tetragonal-to-cubic phase transitions, for increasing CaO and Y 2 O 3 contents, are both related to variations in the local symmetry of the Zr-O first neighbor coordination sphere.
Characterization of Nanocrystalline Yttria-Stabilized Zirconia: An In Situ HTXRD Study
ISRN Nanotechnology, 2011
Nanocrystalline yttria-stabilized zirconia powders, synthesized by the citrate nitrate gel combustion route, with yttria concentration varying from 8 to 12 mol% were studied by in situ high temperature X-ray diffraction in the temperature range of 25-1000 • C. The sample obtained has a high specific surface area of 35 m 2 /g while calculated surface area was around 123 m 2 /g. The in situ high temperature X-ray diffraction study revealed that crystallite size remains in the range of 7-9 nm up to 800 • C and then rapidly grows up to 21-23 nm upto 1000 • C; only holding the material at 1000 • C for 30 minutes can promote grain growth in the range of 42-49 nm. Coefficient of thermal expansion ranges from 9.65 to 9.03 ppm/ • C for 8-12 mol% nanocrystalline yttria-stabilized zirconia.
Sintering of Mechanically Alloyed YSZ Nanocrystalline Powders
Materials Science Forum, 2007
We report on the mechanical and structural properties of nanocrystalline 8% and 10% mol yttria stabilized zirconia (YSZ) obtained using mechanical alloying (MA). For milling times above 32 hours the complete alloying of the starting Y 2 O 3 and ZrO 2 powders is achieved. The asmilled powders show a body-centered cubic crystalline structure with grain sizes in the order of 10 nm. After uniaxial pressing and sintering the compacts exhibit densities of more than 93% of the theoretical value. The microhardness of the compacts increases with sintering temperature, reaching a maximum value of 913 HV0.5 after sintering at 1220º C for 6 hours. The correlation of these enhanced mechanical properties with the microstructural changes induced by heat treatment of the nanocrystalline MA powders is discussed.
Defect studies of nanocrystalline zirconia powders and sintered ceramics
Physical Review B, 2010
The main objective of the present paper is to communicate a study of defects behavior in zirconia-based nanomaterials-pressure-compacted yttria-stabilized zirconia ͑YSZ͒ nanopowders with different contents of Y 2 O 3 and ceramics obtained by sintering the YZS nanopowders. In addition, YZS single crystals were also investigated. Positron annihilation techniques including positron lifetime and coincidence Doppler broadening with a conventional positron source and Doppler broadening experiments on a monoenergetic positron beam were involved in this study as the principal tools. These techniques were supplemented with transmission electron microscopy and x-ray diffraction observations. In order to get better support of the experimental data interpretation, the state-of-art theoretical calculations of positron parameters were performed for the perfect ZrO 2 lattice and selected defect configurations in the YSZ. Theoretical calculations have indicated that neither the oxygen vacancies nor their neutral complexes with substitutional yttrium atoms are capable of positron trapping. On the other hand, the zirconium vacancies are deep positron traps and obviously are responsible for the saturated positron trapping observed in the YSZ single crystals. In the compacted YSZ nanopowders, a majority of positrons is trapped either in the vacancylike defects situated in the negative space-charge layers along grain boundaries ͑ 1 Ϸ 185 ps͒ or in vacancy clusters at intersections of grain boundaries ͑ 2 Ϸ 370 ps͒. The intensity ratio I 2 / I 1 was found to be correlated with the mean grain size d as I 2 / I 1 ϳ d −2 . A small fraction of positrons ͑Ϸ10%͒ form positronium in large pores ͑ 3 Ϸ 2 ns, 4 Ϸ 30 ns͒. A significant grain growth during sintering of the YSZ nanopowders above 1000°C was observed.
Materials, 2021
Mixtures of powders essentially differing in their particle morphology and size were applied to prepare polycrystals in a Y2O3-ZrO2 system. An yttria–zirconia solid solution nanometric powder with a Y2O3 concentration of 3.5% was prepared by subjecting co-precipitated gels to hydrothermal treatment at 240 °C. The crystallization occurred in distilled water. The pure zirconia powders composed of elongated and sub-micrometer size particles were also manufactured through the hydrothermal treatment of pure zirconia gel, although in this case, the process took place in the NaOH solution. Mixtures of the two kinds of powder were prepared so as to produce a mean composition corresponding to an yttria concentration of 3 mol%. Compacts of this powder mixture were sintered, and changes in phase composition vs. temperature were studied using X-ray diffraction. The dilatometry measurements revealed the behavior of the powder compact during sintering. The polished surfaces revealed the microstru...
PALS study on the defect structure of yttria-stabilized zirconia
Radiation Physics and Chemistry, 2007
Powders of stabilized ZrO 2-8 mol% Y 2 O 3 (YSZ) have been obtained by mechanical milling in zirconia vials. The samples were characterized by X-ray diffraction (XRD). Positron annihilation lifetime (PALS) measurements were performed to investigate the lattice defects originated by the incorporation of yttria and those mechanically induced. The XRD results indicate the formation of tetragonal YSZ solid solution. PALS results indicate that positron trapping occurs at different kinds of defects such as vacancy-like defects, grain boundary and associated defects.