Showing papers in "Journal of the American Ceramic Society in 1986"
TL;DR: In this article, a disordered layer structure of Calcium silicate hydrate gel is presented, in which most of the layers are structurally imperfect ones of jennite (Ca9Si6O32H22), and others are similarly related to 1.4-nm tobermorite, both structures being modified by omission of many of their silicate tetrahedra.
Abstract: Calcium silicate hydrate gel is a very poorly crystalline material that is the main product of reaction of portland cement with water. Evidence is presented for a disordered layer structure, in which most of the layers are structurally imperfect ones of jennite (Ca9Si6O32H22), and others are similarly related to 1.4-nm tobermorite (Ca5Si6O26H18), both structures being modified by omission of many of their silicate tetrahedra. The evidence comprises conditions of formation, silicate anion type, Ca/Si ratio, H2O/Ca ratios and densities for various drying conditions, thermogravimetric curve, X-ray powder and selected-area electron diffraction patterns, and results of analytical electron microfcopy.
569 citations
TL;DR: In this article, the detrimental aging phenomenon observed in ZrO2-Y2O3 materials was investigated with respect to the gaseous aging environment and the Y 2O3 and SiO2 content of the material and it was shown that the aging phenomenon is caused by water vapor and that intergranular silicate glassy phases play no significant role.
Abstract: The detrimental aging phenomenon observed in ZrO2-Y2O3 materials, which causes tetragonal ZrO2 to transform to its monoclinic structure at temperatures between 150 and 400°C, was investigated with respect to the gaseous aging environment and the Y2O3 and SiO2 content of the material. It is shown that the aging phenomenon is caused by water vapor and that inter-granular silicate glassy phases play no significant role. Transmission electron microscopy of thin foils, before and after aging, showed that the water vapor reacted with yttrium in the ZrO2 to produce clusters of small (20 to 50 nm) crystallites of α-Y(OH)3. It is hypothesized that this reaction produces a monoclinic nucleus (depleted of Y2O3) on the surface of an exposed tetragonal grain. Monoclinic nuclei greater than a critical size grow spontaneously to transform the tetragonal grain. If the transformed grain is greater than a critical size, it produces a microcrack which exposes subsurface tetragonal grains to the aging phenomenon and results in catastrophic degradation. Degradation can be avoided if the grain size is less than the critical size required for microcracking.
360 citations
TL;DR: In this paper, lattice parameter and density data were compiled for Y2O3-Stabilized ZrO2, both from the literature and from experimental measurements, and the data were described very well over a wide range of composition by the model of Aleksandrov et al., which assumes Y substitution for Zr in the unit cell with compensating anion vacancies.
Abstract: Lattice parameter and density data were compiled for Y2O3-Stabilized ZrO2, both from the literature and from experimental measurements. The data are described very well over a wide range of composition by the model of Aleksandrov et al., which assumes Y substitution for Zr in the unit cell with compensating anion vacancies. Effects are noted in two-phase cubic-tetragonal materials which indicate significant lattice strains in the two-phase materials.
338 citations
TL;DR: In this article, the oxidation kinetics of several single-crystal and polvcrystalline silicon carbide materials and singlecrystal silicon in dry oxygen over the temperature range 1200° to 1500°C were fitted to the linear-parabolic model of Deal and Grove.
Abstract: The oxidation kinetics of several single-crystal and polvcrystalline silicon carbide materials and single-crystal silicon in dry oxygen over the temperature range 1200° to 1500°C were fitted to the linear-parabolic model of Deal and Grove. The lower oxidation rates of silicon carbide compared to silicon can be rationalized by additional consumption of oxidant in oxidizing carbon to carbon dioxide. The (000J) Si face of the silicon carbide platelets exhibited lower parabolic oxidation rates than the (0001) C face, by a factor of 10 at 1200°C. Apparent activation energies increased from a value of ∼120 kJ/mol below 1400°C to a value of ∼300 kJ/mol above this temperature. The (0001) Si face exhibited this high activation energy over the entire temperature range. The controlled nucleation thermally deposited material exhibited the highest oxidation rates of the polycrystalline materials followed by the hot-pressed and sintered α-silicon carbides. In general, the oxidation rates of the polycrystalline materials were bracketed by the oxidation rates of the basal planes of the single-crystal materials. Higher impurity concentrations and higher density of nucleation sites led to a greater susceptibility to crystallization of the scale which significantly complicated the oxidation behaviors observed. When crystallization of the oxide scale occurred in the form of a layer of spherulitic cristobalite crystals, a retardation of the oxidation rates was observed. An accelerated oxidation behavior was found when this coherent layer was superseded by the formation of fine mullite crystals.
323 citations
TL;DR: In this paper, the effect of the grain boundary effect on dc ionic conductivity was studied for ceria ceramics doped with trivalent dopants (Y3+, Gd3+, and La3+).
Abstract: The “grain-boundary effect,” which leads to a greatly reduced dc ionic conductivity due to the presence of a blocking layer in the vicinity of the grain boundaries, is studied in detail for ceria ceramics doped with various trivalent dopants (particularly Y3+, Gd3+, and La3+). The effects of porosity, of sintering time, and of dopant size and dopant concentration are investigated. Finally, it is shown that the grain-boundary effect virtually disappears when nearly silicon-free starting materials are used.
288 citations
TL;DR: Two kinds of xerogels were prepared by slow and rapid hydrolyses of tetraethoxysilane and aluminum nitrate nonahydrate dissolved in ethanol as discussed by the authors.
Abstract: Two kinds of xerogels were prepared by the slow and rapid hydrolyses of tetraethoxysilane and aluminum nitrate nonahydrate dissolved in ethanol. Xerogels prepared by slow hydrolysis crystallized mullite directly from the amorphous state on firing whereas those formed by rapid hydrolysis crystallized a spinel phase before mullite formation. The composition of the spinel phase was characterized by various methods to be near SiO2·6Al2O3. The process of mullite formation is discussed in relation to the structures of the starting materials.
282 citations
TL;DR: In this article, the existence of ferroelasticity in tetragonal zirconia was investigated and the reorientation of the domains by externally applied stress was proposed as a toughening mechanism.
Abstract: X-ray diffraction data are presented in support of the existence of ferroelasticity in tetragonal zirconia. Reorientation of ferroelastic domains by externally applied stress is proposed as a toughening mechanism. Toughening by this mechanism can occur in addition to transformation toughening and also explains high toughness of some zirconias which exhibit no transformation to the monoclinic form. Zirconia ceramics toughened by the ferroelastic mechanism have the potential to retain high toughness at elevated temperature unlike transformation toughening.
264 citations
TL;DR: A bending technique for the strength measurement of glass fibers is described and an analysis is presented which determines the effective tested length as a function of the statistical parameters which describe the fracture properties of the fiber as discussed by the authors.
Abstract: A bending technique for the strength measurement of glass fibers is described and an analysis is presented which determines the effective tested length as a function of the statistical parameters which describe the fracture properties of the fiber. The analysis is used to compare strength data determined in both tension and bending for various representative fibers. It is found that the tensile strength cannot be predicted from the strength in bending and vice versa because the tested lengths differ by at least 3 orders of magnitude. Thus, while bending does not replace tension as a measurement technique, it does provide additional valuable information about the flaw size distribution.
253 citations
TL;DR: In this article, a single-phase Ba-Nb-doped BaTiO3 has been prepared with various Ba/(Ti + Nb) ratios such that single phase products will be obtained if the charged donor center is assumed to be compensated in turn by Ba vacancies, Ti vacancies, equal concentrations of the two cation vacancies, oxygen interstitials, or electrons.
Abstract: Nb-doped BaTiO3 has been prepared with various Ba/(Ti + Nb) ratios such that single-phase products will be obtained if the charged donor center is assumed to be compensated in turn by Ba vacancies, Ti vacancies, equal concentrations of the two cation vacancies, oxygen interstitials, or electrons. For air-Fired samples, examination by transmission electron microscopy showed that only the composition adjusted for compensation by titanium vacancies was single phase. The other compositions contained a Ti-rich second phase in order to achieve a matrix with the appropriate concentration of titanium vacancies. When sintered in a reducing atmosphere, compensation was by electrons, and a Ba-rich second phase was present hi the composition adjusted to give compensation by titanium vacancies. The results indicate that for donor concentrations greater than ∼0.5 mol% in BaTiO3, charge compensation is achieved by Ti vacancies under oxidizing conditions, and by electrons (as is well-known) under reducing conditions.' The effect of compensating defects on grain growth is also discussed.
241 citations
TL;DR: Both tetragonal (t) and monoclinic (m) ZrO2 particles in Al2O3 can give rise to toughening, and the residual stresses around already-transformed m-ZrO 2 particles can cause microcracking as discussed by the authors.
Abstract: Both tetragonal (t) and monoclinic (m) ZrO2 particles in ZrO2-toughened Al2O3 can give rise to toughening. In the stress field of propagating cracks, the t-ZrO2 particles can undergo the stress-induced t→m transformation, and the residual stresses around already-transformed m-ZrO2 particles can cause microcracking. The t-ZrO2 particles transformed in crack tip stress fields do not, however, also cause appreciable microcracking. The toughening increments via these distinct mechanisms are comparable. It appears that optimally fabricated Zr02-toughened Al2O3's should contain a mixture of t- and m-ZrO2.
225 citations
TL;DR: Barium titanate precursors with Ba/Ti ratios ranging from 2:1 to 1:9 were prepared by controlled hydrolysis of mixed barium and titanium species in an alcohol medium.
Abstract: Barium titanate precursors with Ba/Ti ratios ranging from 2:1 to 1:9 were prepared by controlled hydrolysis of mixed barium and titanium species in an alcohol medium. Details of the synthesis and characterization of the resultant products are given. Amorphous powders precipitated by hydrolysis from ethanol solutions of barium and titanium alkoxides crystallize to single-or two-phase 1:2 and 1:5 compounds at ∼700°C. These compounds transform at higher temperatures to other known crystalline phases, the 1:5 phase being maintained metastably to ∼1100°C.
TL;DR: In this paper, the authors have shown that solid-solution formation with SnO/sub 2/, as in commercial dielectric compositions, is effective in stabilizing the high-temperature structure of these materials.
Abstract: ZIRCONIUM TITANATE solid solutions are of interest for their useful dielectric properties in the microwave frequency regime. The authors have shown that solid-solution formation with SnO/sub 2/, as in commercial dielectric compositions, is effective in stabilizing the high-temperature structure of these materials. This high-temperature structure is of the type known as ..cap alpha..-PbO/sub 2/, space group Pcnb, number 60. The space group implies a random cation distribution on the available sites and has been confirmed using Reitveld total profile analysis of neutron powder diffraction data obtained using specimens prepared during this work. Single-phase, ..cap alpha..-PbO/sub 2/-type zirconium titanate solid solutions with compositions Zr/sub 1+x/Ti/sub 1-x/O/sub 4/ (1/10 > x > - 1/6) can be prepared by solid-state reaction. The phase transition, as observed during cooling is characterized by a gradual contraction of the unit-cell volume in the temperature range 1400/sup 0/ to 1050/sup 0/C. A major inflection, especially apparent in the c-axis length, is observed between 1200/sup 0/ and 1100/sup 0/C.
TL;DR: In this paper, the local structural environments of Y/sup 3 +/ and Zr/sup 4 +/ in 18 wt% Y/sub 2/O/sub 3/-stabilized zirconia were studied using extended X-ray absorption fine structure spectroscopy over the temperature range.
Abstract: The local structural environments of Y/sup 3 +/ and Zr/sup 4 +/ in 18 wt% Y/sub 2/O/sub 3/-stabilized zirconia were studied using extended X-ray absorption fine structure spectroscopy over the temperature range - 120/sup 0/ to 770/sup 0/C. The measured cation-oxygen distances reflect those of the parent oxides, with the mean Zr-O distance 0.017 nm shorter than the mean Y-O distance. The spread in the Zr-nearest-neighbor and Zr-next-nearest-neighbor distances is considerably larger than observed for Y/sup 3 +/. This result is attributed to the anion vacancies being preferentially sited adjacent to the smaller Zr/sup 4 +/ cation which, with ensuing relaxations, permits a closer contact between Zr/sup 4 +/ and its oxygen neighbors. Thus, the structural environment of these Zr/sup 4 +/ ions resembles that of the 7-coordinated Zr/sup 4 +/ in monoclinic zirconia. Increasing the temperature of the sample results in the local structural environments of the two cations becoming more alike, suggesting that increased anionic mobility leads to an increasingly random distribution of anion vacancies.
TL;DR: In this article, two mechanisms are proposed for the limitation of strength in transformation-toughened zirconia ceramics: the strength is limited by the critical stress to induce the tetragonal-to-monoclinic phase transformation and that the inherent R-curve behavior of these materials limits the strength.
Abstract: Two mechanisms are proposed for the limitation of strength in transformation-toughened zirconia ceramics: that the strength is limited by the critical stress to induce the tetragonal-to-monoclinic zirconia phase transformation and that the inherent R-curve behavior of these materials limits the strength. Experimental evidence to support both mechanisms is presented which agrees tolerably well with theoretical predictions. However, for materials with larger initial flaws and higher toughness the experimental results favor the R-curve argument.
TL;DR: In this article, the lattice vibrations of Ba(Zn,Ta)O3 and BaZrO3 solid solutions, far infrared reflection spectra were measured from 50 to 4000 cm−1 using a Fourier transform infrared spectrometer.
Abstract: The dielectric ceramic materiala Ba(Zn1/3Ta2/3)O3–BaZrO3 has extremely low dielectric loss at microwave frequencies. To investigate the lattice vibrations of Ba(Zn,Ta)O3 and Ba(Zr, Zn, Ta)O3 solid solutions, far infrared reflection spectra were measured from 50 to 4000 cm−1 using a Fourier transform infrared spectrometer. These data were analyzed according to the classical dispersion theory. The spectra of Ba(Zn,Ta)O3 are well fitted by using the 14 resonant modes, and the spectra of Ba(Zr, Zn, Ta)O3 solid solution are fitted by assuming the normal distribution on resonant frequencies. The damping constant of these materials is discussed, and the values of tan δ calculated from the dispersion parameters agree with the measured values.
TL;DR: In this article, the effect of MgO as a solid-solution additive in the sintering of Al2O3 was studied and the separate effects of the additive on densification and grain growth were assessed.
Abstract: The effect of MgO as a solid-solution additive in the sintering of Al2O3 was studied. The separate effects of the additive on densification and grain growth were assessed. Magnesia was found to increase the densification rate during sintering by a factor of 3 through a raising of the diffusion rate. The grain-size dependence of the densification rate indicated control primarily by grain-boundary diffusion. Magnesia also increased the grain growth rate during sintering by a factor of 2.5. The dependence of the grain growth rate on density and grain size suggested a mechanism of surface-diffusion-controlled pore drag. It was argued, therefore, that MgO enhanced grain growth by raising the surface diffusion coefficient. The effect of MgO on the densification rate/grain growth rate ratio was, therefore, found to be minimal and, consequently, MgO did not have a significant effect on the grain size/density trajectory during sintering. The role of MgO in the sintering of alumina was attributed mainly to its ability to lower the grain-boundary mobility.
TL;DR: In this paper, a yield criterion based on both shear and dilatation effects correctly correlates deformation data from tension, compression, bending, and indentation, and further delineates a crack-tip process zone comparable to the one observed experimentally.
Abstract: Transformation plasticity in ZrO2-containing ceramics generally exhibits shear and dilatation effects of comparable magnitude. The coupling between external stresses and crystallographic strains assists the tetragonal-monoclinic transformation, which, via shear localization, gives rise to macroscopic shear and dilatant deformation. Application of a yield criterion based on both shear and dilatation effects correctly correlates deformation data from tension, compression, bending, and indentation, and further delineates a crack-tip process zone comparable to the one observed experimentally. Similar shear and dilatation effects in microcracking due to transformation plasticity are explored. These findings suggest that the strength of the ultimate transformation-toughened structural ceramics should be yield limited and sensitive to the stress state. Strategies for fracture control are recommended.
TL;DR: In this paper, a transformation-toughened MgO-partially-stabiltzed ZrO2 was identified using in situ observations, related to measured stress-strain curves, strengths under various loading conditions, strength degradation from surface damage, and comparative strengths and toughnesses of toughened and overaged materials.
Abstract: Mechanisms of failure in a transformation-toughened MgO-partially-stabiltzed ZrO2 are identified using in situ observations. The observations are related to measured stress-strain curves, strengths under various loading conditions, strength degradation from surface damage, and comparative strengths and toughnesses of toughened and overaged materials. Both reversible and irreversible tetragonal-to-monoclinic transformations, as well as microcracking, are associated with nonlinear stress-strain curves. The influence of this nonlinear response on stresses produced by flexural loading is evaluated. Failure is preceded by stable growth of microcracks, resulting in R-curve behavior and damage-tolerant strength characteristics. The implications of R-curve response for strengthening and toughening characteristics are discussed.
TL;DR: In this paper, the authors measured the time-dependent axial and radial strains in cylindrical specimens of powder compacts when they are sintered under a superimposed uniaxial load and found that the deformation rate of the porous body follows Coble creep behavior except for a stress enhancement factor arising from the reduced effective cross-sectional area from the presence of voids.
Abstract: Kinetics of densification and deformation can be studied simultaneously by measuring the time-dependent axial and radial strains in cylindrical specimens of powder compacts when they are sintered under a superimposed uniaxial load. Such experiments, carried out on powder compacts of magnesia-doped alumina, are reported. Several results have been obtained. The experiments have provided a direct measure of the intrinsic sintering pressure, which we find to lie in the range 0.4 to 0.8 MPa. The deformation rate, or shear rate of the porous body, is found to follow Coble creep behavior except for a stress enhancement factor arising from the reduced effective cross-sectional area from the presence of voids. The rate of densification follows a linear dependence on the total mean pressure and a cubic dependence on the average grain size.
TL;DR: In this article, a tritagonal zirconia polycrystals were produced from high purity powders containing 1.5 to 5.0 mol% Y/sub 2/O/sub 3/ by cold isostatic pressing and sintering.
Abstract: Tetragonal zirconia polycrystals were produced from high purity powders containing 1.5 to 5.0 mol% Y/sub 2/O/sub 3/ by cold isostatic pressing and sintering, hot-pressing, and hot isostatic pressing. The mechanical properties and microstructures of these resulting materials were examined, with emphasis on the relation between strength and fracture toughness.
TL;DR: In this article, the average grain size of ZrO2(+Y, o) materials sintered at 1400°C was observed to depend significantly on the Y2O3 content.
Abstract: The average grain size of ZrO2(+Y, o,) materials sintered at 1400°C was observed to depend significantly on the Y2O3 content. The average grain size decreased by a factor of 4 to 5 for Y2O3 contents between 0.8 and 1.4 mol% and increased at Y2O3 contents of 6.6 mol%. Grain growth control by a second phase is the concept used to interpret these data; compositions with a small grain size lie within the two-phase tetragonal + cubic phase field, and the size of the tetragonal grains is believed to be controlled by the cubic grains. This interpretation suggests that the Y2O3-rich boundary of the two-phase field lies between 0.8 and 1.4 mol% Y2O3. Transformation toughened materials fabricated in this binary system must have a composition that lies within the two-phase field to obtain the small grain size required, in part, to retain the tetragonal toughening agent.
TL;DR: A mathematical model which simulates the development of microstructure during the hydration of tricalcium silicate (C3S) is described in this article, which is part of a program to develop a model which will quantitatively connect variables associated with different observable characteristics in cement-based systems, from the time of mixing onwards.
Abstract: A mathematical model which simulates the development of microstructure during the hydration of tricalcium silicate (C3S) is described. It is part of a program to develop a model which will quantitatively connect variables associated with different observable characteristics in cement-based systems, from the time of mixing onwards. The core of the model is a mathematical description of all significant aspects of a selected volume of hydrating material. Output is either a numerical description of some aspect of the system or a graphic representation of the microstructure. The model is versatile and interactive and provides the ability to test the consequences of individual hypotheses in a system which has complex interconnected cause-effect relationships. It has the potential for predicting microstructure and bulk properties resulting from a wide variety of hydration conditions. It might also serve as a prototype for other materials which are formed through reaction bonding of powder compacts, including fired ceramics, chemically bonded ceramics, and products of powder metallurgy.
TL;DR: In this article, the effect of small uniaxial stresses on the sintering of CdO powder compacts was studied using a loading dilatometer, where compacts of two different green densities were sintered at 1123 K and subjected to stresses between 0 and 0.25 MPa.
Abstract: The effect of small uniaxial stresses on the sintering of CdO powder compacts was studied using a loading dilatometer. Compacts of two different green densities were sintered at 1123 K and subjected to stresses between 0 and 0.25 MPa. Densification and creep occur simultaneously, and the effects of these two processes can be separated. Between relative densities of 0.5 and 0.9, the dependence of the uniaxial creep rate on density can be described in terms of a stress intensification factor which depends exponentially on the porosity but is independent of the grain size. Comparison of the densification and creep rates permits definition of the sintering stress, which is found to decrease with increasing density, and verification of the Zener relation. The stress and grain size dependence of the creep rate, and the grain size dependence of the densification rate, support grain-boundary diffusion as the rate-controlling step in both processes.
TL;DR: In this paper, the thermal expansion of the skeletal framework was essentially zero for NaZr2(PO4)3-type compounds; the interstitialion, e.g., Na+, was primarily responsible for the total thermal expansion.
Abstract: The thermal expansion of the skeletal framework was essentially zero for NaZr2(PO4)3-type compounds; the interstitialion, e.g., Na+, was primarily responsible for the total thermal expansion. The composition dependence of the thermal expansion is discussed in terms of the amounts, crystallographic sites, and ionic radii of the interstitial ions. The mechanism which results in low thermal expansion was clarified, particularly for KZr2(PO4)3, in which a larger ion is substituted for Na+, and NbZr(PO4)3, which does not contain Na+. Polycrystalline ceramics formed from these crystals might be useful as thermal-shock-resistant materials.
TL;DR: In this article, effective sintering aids for SiC ceramics are discussed on the basis of their reactivities with various sinterings aids around sinter-ing temperatures (2300 to 2400 K).
Abstract: Effective sintering aids for SiC ceramics are discussed on the basis of their reactivities with various sintering aids around sintering temperatures (2300 to 2400 K). The free energy consideration of the reactions suggests that metals and metal oxides which do not decompose SiC in the sintering process are effective as sintering aids for SiC ceramics.
TL;DR: In this article, the authors investigated the role of free energy on subsequent transformation nucleation during degradation of tetragonal polycrystalline t-ZrO2 polycrystals with 2 and 3 mol% Y2O3.
Abstract: Various aspects of the tetragonal (t) to monoclinic (m) transformation during degradation have been studied experimentally and theoretically in yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), i.e., polycrystalline t-ZrO2 containing Y2O3 in solution. Transmission electron microscopy (TEM) revealed that protruding grains at the surface of Y-TZP specimens do not transform under corrosive conditions (250°C, humid atmosphere) even after an annealing time of 168 h. Eigenstresses due to anistropic thermal expansion In and around protruding and bulk grains have been calculated for Y-TZP containing 2 and 3 mol% Y2O3. The prominent role of these stresses on subsequent transformation nucleation during degradation is shown to agree qualitatively with an established free energy concept. The lack of complete transformation of m-ZrO2 is attributed to characteristics of the nucleation- and growth-controlled transformation process.
TL;DR: In this paper, the concentrations of lime and silica in the aqueous phase which is in contact with calcium silicate hydrate are analyzed and some important insights emerge for the understanding of the complex processes which occur during the hydration of tricalcium silicate.
Abstract: There are many published values for the concentrations of lime and silica in the aqueous phase which is in contact with calcium silicate hydrate. These have been collected, carefully analyzed, and found often to be apparently inconsistent. When, however, they are interpreted as having come from an aqueous phase which is in near equilibrium with one or another of two possible modifications of calcium silicate hydrate, almost all the data are rationalized. Some important insights emerge for the understanding of the complex processes which occur during the hydration of tricalcium silicate.
TL;DR: The theory of colloidal filtration in slip casting of ceramics as developed by Aksay and Schilling for incompressible cakes has been extended to compressible materials as mentioned in this paper.
Abstract: The theory of colloidal filtration in slip casting of ceramics as developed by Aksay and Schilling for incompressible cakes has been extended to compressible materials. The rate of cake deposition in the mold depends upon the capillary pressure and permeability of the mold. Assuming that the capillary pressure is inversely proportional to an average diameter typifying the mold and that the permeability is directly proportional to the square of the diameter, an optimum diameter exists for production of maximum pressure drop across the cake and maximum rate of deposition.
TL;DR: In this paper, the defect structure in 3 mol% Y-TZP was studied by correlated internal friction, dielectric loss, and ionic conductivity experiments, and the relaxation parameters were determined as Hm= 90 ± 3 kJ·mol−1, τ∞= (1.0+1.5−0.6) × 10−14 s for the mechanical relaxation.
Abstract: The defect structure in 3 mol% Y-TZP was studied by correlated internal friction, dielectric loss, and ionic conductivity experiments. A prominent mechanical and dielectric loss peak occurs in the temperature range between 380 and 550 K that depends on the frequency of measurement. The relaxation parameters were determined as Hm= 90 ± 3 kJ·mol−1, τ∞= (1.0+1.5−0.6) × 10−14 s for the mechanical relaxation and Hd= 84 ± 3 kJ·mol−1, τ∞= (1.6+1.7−0.9) × 10–13 s for the dielectric relaxation. The ionic conductivity below 790 K is controlled by an activation enthalpy of Hσ= 89 ± 3 kJ·mol−1; at higher temperatures Hσ= 60 ± 3 kJ·mol–1. An atomistic model is presented which assumes that oxygen vacancies are trapped by yttrium ions forming anisotropic complexes which—by reorientation—cause anelastic and dielectric relaxation. At higher temperatures (>790 K) these complexes are dissociated, which leads to the reduced activation enthalpy for ionic conductivity.