Local electrical and dielectric properties of nanocrystalline yttria-stabilized zirconia

Grain core and grain boundary electrical and dielectric properties of nanocrystalline yttria-stabilized zirconia (YSZ) were analyzed using a novel nano-Grain Composite Model (n-GCM). Partially sintered pellets with average grain sizes ranging from 10 to 73 nm were analyzed over a range of temperatures using AC impedance spectroscopy (AC-IS). Local grain core and grain boundary conductivities, grain boundary dielectric constants, and effective grain boundary space charge widths were determined from the fitted circuit parameters. Required grain core dielectric constant data were provided by AC-IS measurements of single crystal YSZ over a range of temperatures. The local grain core conductivity of all the nanocrystalline samples was slightly decreased with respect to that of microcrystalline YSZ. Conversely, the local grain boundary conductivity was enhanced up to an order of magnitude compared to microcrystalline YSZ. At the nanoscale, there was a noticeable increase in local grain boundary dielectric constant versus single crystal values at the same temperature.     

Phase stability and electrical property of NiO-doped yttria-stabilized zirconia

The effects of NiO solid solution into yttria fully stabilized cubic zirconia (YSZ) on the phase stability and electrical properties of YSZ were investigated. Time-dependent conductivity change of NiO-doped YSZ at 1000 °C was also investigated. Raman spectra showed that weak tetragonal peaks in the YSZ monolith disappeared when NiO was added. In addition, the time-dependent conductivity of YSZ monolith sharply decreased after the first 30 h of annealing at 1000 °C, whereas NiO-doped YSZ did not show such decline. Therefore, the solid solution of NiO enhanced YSZ stability and produced time-dependent conductivity change with moderate time.     

Electrical properties of plasma-sprayed yttria-stabilized zirconia films

Yttria-stabilized zirconia films, 100 to 200 m thick, were prepared by plasma spraying. The electrical properties were investigated by complex impedance spectroscopy. The results are compared with those obtained on sintered pellets prepared with the same powders used for spraying and on commercial single crystals. The ionic conductivity and the activation energies of sprayed films and single crystals are found to be very similar, and no grain-boundary effect is observed in the film complex impedance plots. These results are explained by the high density and purity of the sprayed films.     

Effect of impurities on sintering and conductivity of yttria-stabilized zirconia

The effect of low concentrations of Fe₂O₃, Al₂O₃ and Bi₂O₃ on the sintering behaviour of (ZrO₂)_0.83 (YO_1.5)_0.17, made by alkoxide synthesis, has been investigated. The best results are achieved with Bi₂O₃ as a sinter agent and a relative density of 95% is obtained at 1200 K. The effects of these impurities on the electrical conductivity of the bulk and the grain boundaries has been investigated using frequency dispersion analysis (10¹-10⁶ Hz). All investigated impurities have a negative influence on both the bulk and grain-boundary conductivity. For Fe₂O₃ and Al₂O₃ grain-boundary segregation factors of about two are calculated.     

Influence of alumina dopant on the properties of yttria-stabilized zirconia for SOFC applications

The most important component of the solid oxide fuel cell (SOFC) is the dense electrolyte. Besides gastightness it must fulfill the requirements of good ionic conductivity and stability in reducing and oxidizing atmospheres. For this application yttria-stabilized zirconia is widely used. In this paper the effect of calcination temperature and milling time for zirconia powder stabilized with 8 mol% yttria (8YSZ) on the gastightness of the electrolyte layer was investigated. The influence of the addition of 0.77, 2 and 4 wt% Al₂O₃ to 8YSZ powder on the tightness and the sinterability of the electrolyte layer was studied. The performance of the cell with the electrolyte doped with 0.77 wt% Al₂O₃ was also investigated. The experiments show that the electrolyte layer, which was fabricated from 8YSZ powder (calcined at 1200°C) with particle size distributions of 0.25 m–<0.3 m (d ₅₀), gives the lowest leak rate. The Al₂O₃ added to 8YSZ improved the electrolyte tightness by increasing the sinterability of the electrolyte layer and reducing the sintering time. The performance of a cell with Al₂O₃ added to the electrolyte is better than that of a cell with an electrolyte of pure 8YSZ, especially at operating temperatures between 800 and 900°C.     

The effect of deposition parameters on the properties of yttria-stabilized zirconia thin films

Yttria-stabilized zirconia (YSZ) films were deposited by RF magnetron sputtering in order to examine the effects of sputtering conditions on the properties of the resulting thin-films. X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and scanning electron microscopy (SEM) were used to characterize the films. Additionally, films were deposited on alumina bars to examine the effect of the coatings on the strength of a brittle substrate. RBS analysis indicated that the ratio of oxygen to zirconium in the films varied from 1.84 to 2.10. XRD showed that there was a wide variation in the amount of monoclinic and tetragonal phases that appeared to be related to the O:Zr ratio. Despite these variations, there was no significant difference found in flexural strength found among the groups of alumina bars that were coated with YSZ. The likely cause is the columnar grain morphology of the deposited thin-films, which does not allow strengthening mechanisms to become operative.     

Effect of copper oxide on the polymorphism of unstabilized and yttria-stabilized zirconia

We have studied the effect of copper oxide doping on the phase composition of unstabilized and yttria partially and fully stabilized zirconia prepared via hydroxide precipitation followed by heat treatment at different temperatures. Copper oxide is shown to stabilize cubic zirconia only in the presence of yttria. The chemical processes in the CuO-Y₂O₃-ZrO₂ system and the mechanisms of C-ZrO₂ stabilization are discussed.     

Effect of boron oxide on the cubic-to-monoclinic phase transition in yttria-stabilized zirconia

Specimens of yttria fully stabilized zirconia with different amounts of boron oxide have been studied by X-ray diffraction at room temperature and at higher temperatures up to 1250 °C. A boron oxide-assisted cubic-to-monoclinic phase transformation was determined in the temperature range 800-1250 °C. In situ high temperature X-ray diffraction experiments gave evidences of the dependence of the phase transformation on the heating rate. The possibility of tuning the cubic-monoclinic phase ratio by suitable addition of boron oxide before pressing and sintering is proposed.     

The microstructure and mechanical properties of yttria-stabilized zirconia prepared by arc-melting

The microstructure of ZrO₂-Y₂O₃ alloys prepared by arc-melting was examined mainly by electron microscopy. It was found that the microstructure changed markedly with yttria content between 0 and 8·7 mol%. Pure zirconia was a single monoclinic phase, while ZrO₂-8·7 mol% Y₂O₃ alloy was single cubic phase as expected from ZrO₂-Y₂O₃ phase diagram. Tetragonal phase was found in alloys with 1 to 6 mol% Y₂O₃ together with monoclinic or cubic phase. The tetragonal phase found in present alloys normally had a lenticular shape with a length 1 to 5m and a width 0.1 to 0.3m, which is much larger than that formed by annealing. The phase with a herring-bone appearance was found in alloys with Y₂O₃ between 2 and 3 mol%, which was recognized to be a metastable rhombohedral phase. The structure of the present alloys is likely to be formed by martensitic or bainitic transformation during fairly rapid cooling from the melt temperature. The change in hardness and toughness with yttria content of the alloys is discussed on the basis of microstructural observations.     

Effects of Fe2O3 doping on structural and electrical properties of 8 mol% yttria-stabilized zirconia electrolyte for solid oxide fuel cells

Journal of Materials Science: Materials in Electronics - The effects of doping a trace of Fe2O3 on the structural and electrical properties of 8&nbsp;mol% yttria-stabilized zirconia (8YSZ) are...     

Xe+离子注入对单晶YSZ光学性能影响的研究

单晶YSZ(ytttia-stabilized cubic zirconia)在注入能量为200keV的Xe+离子后由无色透明变成紫色透明,吸收光谱测试表明,当注量达到1×1016cm-2时,开始出现吸收峰,并且吸收强度随注量增加而增大.对注量为1×1016cm-2和1×1017cm-2的样品,吸收带峰值分别位于522nm和497nm.吸收带可能与氧空位捕获电子形成的F型色心和氧离子捕获空位形成的V型色心有关.注入注量为1×1016cm-2样品的荧光测试表明,荧光光谱均为400～600nm范围内的宽发射带.注入注量为1×1017cm-2的样品没有荧光现象产生,可能是由于辐照损伤严重,缺陷浓度增大所致.     

Robocasting of dense yttria-stabilized zirconia structures

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions (<38 vol%). The sintered structures were able to retain the original morphologies with >94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.     

Effect of different electrode materials on electrophoretic depositional behavior of yttria-stabilized zirconia powder

The electrophoretic depositional (EPD) behavior of yttria-stabilized zirconia (YSZ) powder with 8 mol% Y₂O₃, which is a common material for oxygen sensors as a solid electrolyte, was investigated on stainless steel and carbon based substrates. Ethanol + HNO₃ based suspensions were used for the EPD experiments, and three different YSZ powders, one commercially available powder and two own-made coprecipitated powders, were deposited. The latter powders were calcined at 900 and 1200 °C, respectively. The concentration of the suspension was 3 g/300 cm³ and a small amount of HNO₃ solution was added as a dispersant. A DC electric field of 100–200 V/15 mm was applied between parallel electrodes. On stainless steel electrodes it was found that the own-made coprecipitated powder calcined at 1200 °C, showing the best deposition properties, whereas the commercial YSZ powder showed the best depositional properties on carbon electrodes. These characteristic depositional behaviors are discussed with regard to the adhesive force between the particles and the different electrodes, and some powder properties, e.g., particle size distribution and packing behavior.A thick, continuous, free-standing YSZ film with a thickness of around 10 μm was successfully obtained after firing the deposit on the carbon electrode in flowing air.     

固相含量对氧化钇稳定氧化锆性能的影响

主要研究料浆固相含量对氧化钇稳定氧化锆料浆流变性质,以及YSZ的微结构、密度和强度的影响规律,并分析讨论其原因。结果表明不同固相含量的氧化钇稳定氧化锆料浆表现为剪切变稀的特征,随固相含量增加,坯体密度增加,强度降低,而烧结体密度是先增加后减少的,固相含量为53%(体积分数)时,坯体比较均匀,气孔少。     

Effect of additions of TiO2, SnO2, and Al2O3 on electrical properties of tetragonal zirconia

Abstract

The effect of additions of TiO₂ and SnO₂ on the tetragonal phase of the ZrO₂–Y₂O₃ system has been investigated using complex impedance, X-ray, and transmission electron microscopy measurements. Neither addition acts to stabilize the tetragonal phase and SnO₂ increases the specific grain boundary resistance by a factor of 3. Additions of Al₂O₃ improve the specific grain boundary conductivity of GPR (general purpose reagent) grade material to a level comparable to that of commercially available grades of tetragonal zirconia.

MST/558     

Preparation and characterization of yttria-stabilized zirconia nanotubes

Yttria-stabilized zirconia (YSZ) nanotubes were synthesized by the sol–gel method using porous anodic alumina oxide (AAO) as the templates. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersion X-ray (EDX) spectrum and selected area electron diffraction (SAED) techniques were used to characterize the morphology and crystalline structure of the prepared YSZ nanotubes. The length and the diameter of the YSZ nanotubes are 50 μm and 200 nm, respectively, which are in good agreement with the dimensions of the template pores, while the wall thickness of the nanotubes depends on the impregnation time. XRD and SAED measurements indicate that the obtained YSZ nanotubes after sintering at 1073 K possess a polycrystalline structure and a cubic crystal phase. Brunauer–Emmett–Teller (BET) measurement shows that the YSZ nanotubes have a surface specific area of around 40.5 m² g⁻¹ that is higher than that corresponding to the YSZ nanopowders.     

Influence of copper- and iron-doping on cubic yttria-stabilized zirconia

Cubic yttria-stabilized zirconias (YSZs) (15 mol% Y₂O₃) doped with 2 wt% CuO and 0.3 wt% Fe₂O₃, respectively, have been compared with undoped YSZ. The lattice constants were found to increase in the sequence:a _YSZ <a _YSZ/Fe <a _YSZ/cu. Vickers microhardness of polycrystalline YSZ/Fe exceeds that of polycrystalline YSZ/Cu, whereas the hardness of the single crystalline materials YSZ/Fe and YSZ/Cu are nearly identical and consistently lower than the polycrystalline values. Raman and infrared spectra reveal a breakdown of the selection rules, i.e. these techniques probe the local, non-cubic arrangement of oxygen vacancies. The findings are discussed in terms of a substitutional versus an interstitial-doping model.