Energy selected imaging with a Zeiss 912 ω-filter TEM was used to examine grain boundary solute distributions in an Si3N4/SiC(w) ceramic densified with Y2O3 + Al2O3 sintering aid. These results are compared to boundary region solute distributions in the same materials determined by field emission small probe electron energy loss spectroscopy and related methods. The intrinsic higher incident flux of the FEG small probe methods renders them the most useful for high spatial resolution local chemical width measurement. Energy selected imaging is fast and relatively simple for determining elemental distributions in boundaries at low magnifications. The methods are complementary.

Contact angles and spreading rates of liquids on solids are oft characterized owing to the widespread importance of wetting. Particularly with dissimilar materials, such as liquid metals on ceramics, where wetting can be poor, additives that can induce various reactions often promote wetting, even if it preceeds the reaction. However, excessive or unwanted reaction can equally well be detrimental in other metallic or ceramic systems. Despite obvious needs, mechanisms of reactive wetting are poorly known.

An effort is described to categorize sessile or spreading drop situations having a potential for some degree of reaction and ways wherein the driving force for reaction can actually couple with or parallel that for fluid flow. Several categories where reactivity enhances or retards spreading are described for which the very existence typically depends upon kinetic or nucleation limitations; this includes defining situations in which metastable interfaces have a meaningful context and unique properties. Examples use pairs of inorganic materials, for which the solid may only rarely be truly inert.

Diffusion-induced grain boundary migration is observed during internal reduction of chromium-doped alumina. It occurs because grain boundary diffusion is fast compared to lattice diffusion of oxygen. The oxygen chemical potential relaxes between grain boundaries and adjacent grains. Migration to either side of the boundary is controlled by multiple factors: chemical composition differences between adjacent grains, elastic strain energy differences on the two sides of the boundary plane or by more rapid oxygen relaxation when the c-axis of a grain is perpendicular to the boundary plane.

The study of the migration of the first-order paraelectric-ferroelectric interfaces in BaTiO3 under the hydrostatic pressure is provided in the framework of the time-dependent Ginzburg-Landau theory. The analytical solution describing the interphase boundary is applied for the calculations of its width and velocity at different pressures. The calculations are based on the experimental data for BaTiO3. The parameters of the power law of the temperature and pressure dependences of the interface velocity under the temperature and pressure were obtained. Using the BaTiO3 example we illustrate the ability of the suggested approach in the description of the kinetics of the first-order ferroelectric phase transition in perovskites.

Controlled-geometry pore structures were introduced into undoped and Ti-doped sapphire using microfabrication techniques, and subsequently transferred to internal sapphire-sapphire and sapphire-polycrystalline alumina interfaces via hot pressing. The high-temperature evolution of several different types of structures was examined, in order to isolate different surface properties and evolution processes which are of interest during sintering. A study of pore channel breakup showed that Ti strongly stabilizes channels oriented in the sapphire [1100] direction, suggesting a significant alteration of the Wulff plot. In another study, the equilibration rate of isolated pores was enhanced in Ti-doped sapphire; as glassy phases are unlikely in this material, a solid-state diffusion mechanism for this enhancement is suggested. The evolution of pore channels with pre-existent perturbations was also studied, and the results of these studies are presented.

The discontinuous dissolution of oxide particles has been investigated in the Al2O3 -Fe2O3 system by changing oxygen partial pressure (PO2) and temperature. In PO2 change experiment, 95Al2O3-5Fe2O3 (in wt%) powder compacts were sintered at 1500°C in PO2=0.001 atm and then annealed at 1500°C in air. In temperature change experiment, 85Al2O3-15Fe2O3 (in wt%) powder compacts were sintered at 1600°C in air and then annealed at 1450°C in air. During annealing the sintered specimens, which contained corundum grains and iron aluminate spinel particles, the grain boundaries migrated concomitantly with the dissolution of spinel particles. A discontinuous dissolution of spinel precipitates thus occurred, when the grain boundary migration of alumina in a two phase mixture of corundum and spinel was induced by PO2 or temperature change. The present result would be a distinct observation of the discontinuous dissolution of precipitates in ceramic systems.

A series of spinels were grown by topotaxial solid state reaction on MgO(001) and sapphire(11.2) substrates. The structure of the various spinel/oxide reaction fronts was investigated by cross-sectional high resolution electron microscopy and other methods. While for extremely low misfit the reaction front is completely coherent, different interfacial defects form in other cases, depending on sign and amount of the spinel/oxide lattice misfit. For a large positive misfit, a network of misfit dislocations occured all running along <100<, with Burgers vectors of types a/2[101] and a/2[011] pointing out of the interface. The perpendicular Burgers vector component along [001] permits these dislocations to glide in order to cope with the advancing reaction front, avoiding kinetically unfavourable climb processes. The latter have, however, been observed in negative misfit, where the interfacial dislocations run along <110>, with their Burgers vectors lying in the interface plane. At the sapphire/MgAl2O4 front the structure is completely different. Here the h.c.p.-type oxygen sublattice of sapphire is reconstructed into the f.c.c-type oxygen sublattice of the spinel, which requires a tilt of the MgAl2O4 lattice and the formation of interfacial ledges.

Using tabulated thermodynamic data, a comprehensive investigation of the thermodynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient thermodynamic data exists to conclude that all binary oxides except the following are unstable in contact with silicon at 1000 K: LiO2, the alkaline earth oxides (BeO, MgO, CaO, SrO, and BaO), the column IIIB oxides (Sc2O3, Y2O3, and Re2O3 where Re is a rare earth), ThO2, ZrO2, HfO2, and Al2O3. Of these remaining oxides, sufficient thermodynamic data exists to conclude that MgO, CaO, and ZrO2 are thermodynamically stable in contact with silicon at 1000 K.

The aim of the paper is to explain the recently observed de-wetting grain boundary transition with increasing temperature. On the example of a bicrystal from the Fe-6at.%Si alloy, it was found recently that as temperature is increased, the following GB transitions take place: “solid” (or regular) GB-→“premelted” GB →“solid” GB. At the same time the wetting/de-wetting transitions have taken place. Another example of such GB behavior was discovered during sintering of alumina. The inverse melting behavior is explained as follows: low melting point impurities cause GB premelting at low temperatures, However de-segregation of impurities at high temperatures causes return of the GB structure to its regular “solid” state.

Unidirectional solidification experiments were carried out at the eutectic composition of the systems CoO-ZrO2(CaO) and Co1-xNixO-ZrO2(CaO) yielding materials made of regularly aligned lamellar structures. These eutectic samples were submitted to a high temperature chemical oxidation treatment under oxygen, in conditions where CoO should be oxidized into Co3O4. The study of partially oxidized samples shows that Co3O4 is formed by two mechanisms which are presented together with the corresponding kinetics.

The structures of all the prominent ceramic dielectric resonators have been found to exhibit extensive inhomogeneity. This structural disorder arises from the formation of extended defects, polytype intergrowths or variable degrees of cation order. For the systems involving a cation order-disorder reaction, e.g. ZrTiO4 and Ba(Zn1/3Ta2/3)O3, the formation of internal interfaces can have a pronounced effect on the dielectric properties. In the absence of secondary dopants the lattice strains associated with the interfaces increase the dielectric losses by as much as two orders of magnitude. However, the contributions of the interfaces can apparently be controlled, and perhaps eliminated, by introducing selected dopants that segregate and stabilize the local boundary regions.

An atomic force microscope is used for visualization and control of domain structure in the ferroelectric crystal guanidinium aluminum sulfate hexahydrate (GASH). Large built-in domains are delineated due to the tip-sample electrostatic interaction by the force microscope operating in friction mode. It is found that an applied voltage of a particular sign created new domains whereas a potential of opposite sign erased these domains. Domains created by an external electric field are visualised in topography mode due to piezoelectric deformation of the crystal. The dynamics of domain lateral growth has been directly observed with nanoscale resolution.

This contribution summarizes former results and presents recent findings concerning interfacial properties in solid state ionics but also stresses the model role of ionic conductors for typical ceramic problems. Moreover, recently developed and improved electrochemical techniques allowing spatial resolution are discussed, viz. a two-dimensional impedance spectroscopy as well as a combination of microelectrochemistry and atomic force microscopy.

A large enhancement in the ionic conductivity of certain compounds occurs when the compound is produced as a composite material containing a finely-dispersed non-conductor such as SiO2 or Al2O3 This effect has been reported on for more than 20 years, and it is well established that the enhancement is associated with the presence of interfaces. The popular explanation has been based on a model which contends that the enhancement is due to a space-charge layer which forms to compensate a net charge layer at an interface. A different model proposes that extended defects such as dislocations and grain boundaries, either resulting from or stabilized by the interface, are responsible for the enhancement. This paper describes recent experiments which strongly support the latter model. The ionic conductivities of LiI and CaF2 thin films grown on sapphire(0001) substrates were monitored in-situ during deposition as a function of film thickness and deposition conditions. LiI films grown at 27°C exhibited a region of enhanced conduction within 100 nm of the substrate and a lesser enhancement as the film thickness was increased further. This conduction enhancement was not stable but annealed out with a characteristic log(time) dependence. The observed annealing behavior was fit with a model based on dislocation motion which implies that the increase in conduction near the interface is due to extended defects generated during the growth process. LiI films grown at higher temperatures (100°C) in order to reduce the grown-in defects showed no interfacial conduction enhancement. X-ray diffraction measurements suggest that these high-temperature LiI films nucleate as faceted epitaxial islands with a stable misfit dislocation density defined by the epitaxial relationship between the substrate and film. CaF2 films grown at 200°C showed a behavior similar to the 27°C LiI films, with a region of thermally unstable enhanced conduction that occurs within 10 nm of the substrate. Amorphous Al2O3 films deposited over the CaF2 layers created no additional enhancement but did increase the stability of the conduction, consistent with an extended defect model. Simultaneous deposition of CaF2 and Al2O3 produced films consisting of very-fine-grained CaF2 and particles of amorphous Al2O23 (5-10 nm grain and particle size) and a high defect density which was stable even well above the growth temperature. Measured conduction in the composite at 200°C was approximately 360 times that of bulk CaF2.

Oxygen grain boundary diffusion has been studied in low energy (∑5, ∑13) and high energy (asymmetric 16° tilt) MgO grain boundaries. Enhanced diffusion of oxygen was observed in all boundaries, but more so in the general, high energy boundary, by 1 - 2 orders of magnitude. This supports the theory that the better the atomic registry between the adjoining grains the lower the diffusivities in the grain boundary. Also the activation energies for bulk and grain boundary diffusion (in the ∑13 boundaries) were found to be equal to within experimental error. (≈ 3.9eV)

Electrical properties of ZnO-CuO ceramic composites with varying composition were investigated. The electrical conductivity increased with increasing CuO volume fraction between 1 mol% to 95 mol%. Impedance response showed three semicircles, indicating three resistive elements contributing to the total resistance of the composite. A new model based on the equivalent circuits was developed to explain the contribution of grain boundaries to the resistance of the composite. The change of electrical conductivity was explained by the probability change of two equivalent circuits.

Variations in local electric fields near individual grain boundaries have been observed in TiO2 with an ac, non-contact, atomic force microscopy detection scheme. A lateral, in-plane bias was applied to the sample inducing an electric field gradient. A modified AFM then allowed accurate force and force gradient images of both topography and the electric fields to be measured. The sample-tip separation and bias dependence of the AFM probe response to electrostatic fields are used to derive the relationships that allow quantification of lateral fields. With this technique, observation and quantification of potential barriers and enhancement and depletion widths may be observed, especially as a function of boundary chemistry and orientation. Results are discussed in terms of interface potential barrier models.

It is well known that in many cases, the structure of interfaces is well described in terms of “good matching” islands, separated by misfit dislocations. The “0” lattice theory can predict the dislocations' spacing but not their core width. In the present paper, a new physical parameter: p, called further “localization parameter”, is introduced. It permits the assessment of the width of misfit dislocations. p is expressed as p=EAB/E where EAB is the bonding energy of the two crystals and E is their average cohesion energy. The localization parameter was calculated for about 30 interfaces: metal/metal, metal/ceramics, ceramics/ceramics. For p<0.25, misfit dislocations are delocalized.

The properties of a series ceramic bimorph structure were studied in this paper. The two components of the bimorph were PLZT ceramics with different transition temperatures. The properties of the series bimorph were strongly influenced by the space charge that appears due to the inhomogenities in resistance and dielectric constant.. Some theoretical considerations were made regarding the electric fields that appear inside the bimorph, when heated. It is shown that the value and the direction of these fields could suffer considerable changes in a bimorph structure, compared with the situation when each of the two components is heated separately. The possibility to obtain structures with improved pyroelectric coefficient was put into evidence.