The influence of alumina on the microstructure and grain boundary conductivity of yttria-doped zirconia (original) (raw)
Related papers
Yttria-zirconia: Effect of microstructure on conductivity
Journal of Materials Science, 1987
Complex impedance measurements and detailed analysis of the grain-boundary microstructure have been made on fully stabilized yttria-zirconia sintered bodies as a function of grain size. The prereacted yttria-zirconia powder used in this study was obtained from a commercial source. The powder has very high reactivity and starts sintering around 1 200 ° C. The densification process is complete around 1 350°C but the grain growth continues almost linearly with sintering temperature. The grain size variation obtained was between 1 and 30#m. The grainboundary resistivity when plotted against grain size showed an inflection in the vicinity of 1 500°C sintering temperature. These results have been explained in terms of the grainboundary microstructure changing with the sintering temperature. The thickness of the grainboundary layer determined from impedance data and transmission electron micrographs are in reasonably good agreement. The activation energy for the grain-boundary resistivity was only slightly higher than that for the lattice resistivity.
Microstructure- transport property relation in yttria-doped zirconia
2004
Transmission electron microscopy, XPS analysis, electrical conductivity and diffusion measurements have allowed us to show the microstructure-transport property relation in ZrO 2-9.0 mol% Y 2 O 3 (YSZ) and Al 2 O 3-YSZ composites. Samples with no detectable amorphous grain boundary precipitates show the highest grain boundary electrical conductivity (σ gb) and oxygen diffusion coefficient (D O) values, which decrease in presence of alumina additions. On the contrary, alumina additions (≤ 2 mol%) lead to an increase of the transport properties of samples showing grain boundary glassy films. These results were attributed to a decrease of the grain boundary wettability by the glassy phase when the alumina amount increases. Furthermore, the same grain boundary activation energy found for the different samples show that only ″clean″ grain boundaries contribute to the transport processes
Grain and Grain Boundary Conductivities in Nanocrystalline Yttria-Stabilized-Zirconia Thin Films
ECS Transactions, 2012
Nanocrystalline yttria-stabilized-zirconia thin films with grain sizes smaller than 15 nm are fabricated by spray pyrolysis. Impedance spectroscopy is performed perpendicular to the thin film between room temperature and 600 °C. For a grain size of 13 nm, the grain and grain boundary contributions of the electrical conductivity can be discerned but only between 200 °C and 400 °C. For smaller grains, and higher or lower temperatures, the grain contribution cannot be resolved.
1999
Silica-doped SiO 2 0 À 1X0 wt % 3Y-TZP (3 mol % yttria-doped tetragonal zirconia polycrystal) ceramics are prepared from hetero-coagulated aqueous suspension by colloidal processing. Consolidation of the suspension was carried out by pressure ®ltration at 10 MPa followed by cold isostatic pressing (CIP) at 400 MPa. Consolidated compacts are densi®ed to a relative density over 99% by sintering at 1573 K for 2 h. The formation of glass pockets at grain boundary multiple junctions was observed by SEM for ! 0.5 wt % silica-doped samples. Electrical conductivity measurements were performed to evaluate the modi®cation of grain-boundaries by silica. The apparent grain boundary conductivity decreased with an increase in silica content and became nearly constant above 0.3 wt % of silica, while the bulk conductivity was constant with silica content.
Influence of flash sintering on the ionic conductivity of 8 mol% yttria stabilized zirconia
Journal of the European Ceramic Society, 2018
The ionic conductivity of flash-sintered, polycrystalline 8 mol% yttria stabilized zirconia (8YSZ) was enhanced compared with that of conventionally-sintered specimens. Flash sintering was carried out at a furnace temperature of 850°C with an electric field of 100 V cm-1 to initiate flash. The current density limit was varied between 60 and 100 mA mm-2. Post-flash impedance measurements over the range 215-900°C showed that both bulk and grain boundary conductivities had increased with the increased current density limit which was set prior to flash. The conductivity increases post-flash were ionic, not electronic, although electronic conductivity probably occurred, in addition to ionic conductivity, during flash. The conductivity increases were not attributable to sample densification or microstructural changes. The higher ionic conductivities are attributed to a change in YSZ defect structure that led to an increased concentration of mobile charge carriers; possible explanations for this are discussed. 2. Materials and methods Powders of 8YSZ (Tosoh Corporation, Tokyo, Japan) with manufacturer-specified particle size of 150 nm, were mixed with binder (B
The electrical conductivity of yttria substituted zirconia electrolytes containing glass-forming Si02 and A1203 impurities has been investigated by complex impedance spectroscopy between 450-1270 K. Both fine grained tetragonal ceramics with 3mol% Y203 (3Y-TZP) and coarse grained cubic ceramics with 8mol% Y 203 (8Y-FSZ) have been studied. Al low temperatures, the total conductivity is suppressed by intergranular glass films. These intergranular films have a limited equilibrium thickness of 1-2 nm. A change in slope of the Arrhenius plots of the total conductivity can be observed at the characteristic temperature Tb at which the macroscopic grain boundary resistivity is equal to the macroscopic resistivity of the grains. This behavior can be modelled by a series combination of two resistors using the
Investigation of the electrical conductivity of sintered monoclinic zirconia (ZrO 2 )
Ceramics International, 2017
High-density monoclinic ZrO 2 was manufactured through sintering at~1200°C by using nanosized powders. Then, the electrical conductivity was measured at a range of high temperatures (700-900°C) by electrical impedance spectroscopy (EIS). For the as-sintered monoclinic ZrO 2 , the measured electrical conductivity was 3.2×10 −5 s/cm (for 80% TD) and 4.4×10 −5 s/cm (for 89% TD) at 900°C. After aging at 900°C for 100 h, the electrical conductivity of the monoclinic ZrO 2 of 80%-TD decreased by more than 50%. However, after reheating at 1200°C for 1 h, approximately 80% of the conductivity was recovered compared to the value of the assintered monoclinic ZrO 2. The pure monoclinic crystal structure was retained despite the aging and reheating treatment. Based on microstructural observations of the aged and reheated monoclinic ZrO 2 , the changes in electrical conductivity after aging and reheating were explained by the formation and recovery of micro-cracks, respectively.
Ceramics International, 2011
Densification studies of 8 mol% yttria stabilized zirconia ceramics were carried out by employing the sintering techniques of conventional ramp and hold (CRH), spark plasma sintering (SPS), microwave sintering (MWS) and two-stage sintering (TSS). Sintering parameters were optimized for the above techniques to achieve a sintered density of >99% TD. Microstructure evaluation and grain size analysis indicated substantial variation in grain sizes, ranging from 4.67 mm to 1.16 mm, based on the sintering methodologies employed. Further, sample was also sintered by SPS technique at 1425 8C and grains were intentionally grown to 8.8 mm in order to elucidate the effect of grain size on the ionic conductivity. Impedance spectroscopy was used to determine the grain and grain boundary conductivities of the above specimens in the temperature range of RT to 800 8C. Highest conductivity of 0.134 S/cm was exhibited by SPS sample having an average grain size of 1.16 mm and a decrease in conductivity to 0.104 S/cm was observed for SPS sample with a grain size of 8.8 mm. Ionic conductivity of all other samples sintered vide the techniques of TSS, CRH and MWS samples was found to be 0.09S/cm.HighestconductivityirrespectiveofthegrainsizeofSPSsinteredsamples,canbeattributedtothelowdensificationtemperatureof13258Cascomparedtoothersinteringtechniqueswhichnecessitatedhightemperaturesof0.09 S/cm. Highest conductivity irrespective of the grain size of SPS sintered samples, can be attributed to the low densification temperature of 1325 8C as compared to other sintering techniques which necessitated high temperatures of 0.09S/cm.HighestconductivityirrespectiveofthegrainsizeofSPSsinteredsamples,canbeattributedtothelowdensificationtemperatureof13258Cascomparedtoothersinteringtechniqueswhichnecessitatedhightemperaturesof1500 8C. The exposure to high temperatures while sintering with TSS, CRH and MWS resulted into yttria segregation leading to the depletion of yttria content in fully stabilized zirconia stoichiometry as evidenced by Energy Dispersive Spectroscopy (EDS) studies. #
Ionic conductivity of nanocrystalline yttria-stabilized zirconia: Grain boundary and size effects
Physical Review B, 2010
We report on the effect of grain size on the ionic conductivity of yttria-stabilized zirconia samples synthesized by ball milling. Complex impedance measurements, as a function of temperature and frequency are performed on 10 mol % yttria-stabilized zirconia nanocrystalline samples with grain sizes ranging from 900 to 17 nm. Bulk ionic conductivity decreases dramatically for grain sizes below 100 nm, although its activation energy is essentially independent of grain size. The results are interpreted in terms of a space-charge layer resulting from segregation of mobile oxygen vacancies to the grain-boundary core. The thickness of this space-charge layer formed at the grain boundaries is on the order of 1 nm for large micron-sized grains but extends up to 7 nm when decreasing the grain size down to 17 nm. This gives rise to oxygen vacancies depletion over a large volume fraction of the grain and consequently to a significant decrease in oxide-ion conductivity.