Of the four groups of crystal lattice defects, i.e., point defects, dislocations, interfaces and particles, dislocations are often thought to be the least important for ceramic materials. However, they not only give considerable insight into interfaces (they can be thought of as the link between point defects and interfaces), but they are becoming more important as interest grows in epitactic oxide heterostructures.

The present paper provides a review of our current understanding of dislocations in ceramics. To simplify the discussion, we can separate the task into the following sections, namely

1. Simple oxides (MgO, ZnO etc.)

2. Simple non-oxides (A1N, GaN, SiC, TiC, etc.)

3. More complex binary oxides (AI2O3, Fe203, etc.)

4. Multicomponent oxides and complex non-oxides (spinels, garnets, S13N4)

5. Interfacial dislocations (misfit, grain boundary, etc.)

The features which are most often associated with ceramic materials are their complex structures and large unit cells. For example in bcc garnets, the smallest Burgers vector for a perfect lattice dislocation is ∼0.8nm long.

Lead-based cubic perovskites such as Pb(B2+1/3B5+2/3)O3 (B2+ = Mg, Co, Ni, Zn; B5+ = Nb, Ta) are relaxor ferroelectrics. Localized order and disorder often occur in materials of this type. In the Pb(Mg1/3Nb2/3)O3 (PMN) family, previous studies have proposed two models, space-charge and charge-balance models. In the first model, the ordered regions carry a net negative charge [Pb(Mg1/2Nb,/2)03], while in the second model it does not carry a net charge [Pb((Mg2/3Nb1/3)1/2Nb1/2)03]. However, no direct evidence for these two models has appeared in the literature yet. In this paper we report the first direct observations of local ordering in undoped and La-doped Pb(Mg1/3Nb2/3)03, using high-resolution Z-contrast imaging.

Because the ordered structure in Ba(Mg1/3Nb2/3)03 is well known, the Z-contrast image from an ordered domain is used as a reference for this study. Fig. 1(a) shows the projection of the supercell of fully ordered Ba(Mg1/3Nb2/3)03 along the [110] direction.

The evaluation of the two dimensional projected atom column positions around a defect or an interface in an electronic ceramic, as it has been performed in numerous examples by (quantitative) conventional high-resolution electron microscopy (HRTEM), is often not sufficient to relate the electronic properties of the material to the structure of the defect. Information about point defects (vacancies, impurity atoms), and chemistry or bonding changes associated with the defect or interface is also required. Such complete characterization is a necessity for atomic scale interfacial or defect engineering to be attained.

One instructive example where more than an image is required to understand the structure property relationships, is that of grain boundaries in Fe-doped SrTi03. Here, the different formation energies of point defects cause a charged barrier at the boundary, and a compensating space charge region around it. The sign and magnitude of the barrier depend very sensitively on the atomic scale composition and chemistry of the boundary plane.

In ion irradiation damage studies on ceramics, damage evolution is often assessed using Rutherford backscattering spectroscopy and ion channeling (RBS/C) techniques. In a typical experiment, a single crystal ceramic sample is irradiated with heavy ions and then the crystal is exposed to He ions along a low-index crystallographic orientation. Simultaneously, the backscattered He ion yield is measured as a function of ion energy loss. For He ions scattered from the heavy ion irradiated volume, the He ion yield increases in proportion to the heavy ion dose. The RBS/C yield rises because the He ion beam is dechanneled by, for instance, interstitial point defects and clusters and their associated strain fields. A quantitative measure of dechanneling is denoted by χmin, defined as the ratio of the He ion yield along a low-index crystal orientation, to the yield obtained in a random (non-channeling) orientation. The damage parameter xmin varies from 0 to 1, where 1 represents the maximum damage level that can be measured by RBS/C.

Secondary phases that form during the corrosion of nuclear waste forms may influence both the rate of waste form dissolution and the release of radionuclides [1]. The identification of these phases is critical in developing models for the corrosion behavior of nuclear waste forms. In particular, the secondary uranyl (VI) minerals that form during waste form alteration may control uranium solubility and release of radionuclides incorporated into these phases [2].

The U6+ cation in uranyl minerals is almost always present as a linear (UO2)2+ ion [3]. This uranyl (Ur) ion is coordinated by four, five, or six anions (ϕ) in the equatorial plane resulting in the formation of square (Urϕ4), pentagonal (Urϕ5), and hexagonal (Urϕ6) bipyramids, respectively [3]. These bipyramid polyhedra may polymerize to form complex infinite sheet structures. The linking of Urϕ5 is observed in a number of uranyl minerals formed during waste glass and spent fuel corrosion [2,4], such as weeksite [Na,K(UO2)2(Si205)3*4H2O] and β-uranophane [Ca[(UO2)(SiO3OH)]2*5H2O].

The white lines on the L2,3 absorption edges of the transition metals and on the M4,5 absorption edges of the rare earth elements are the most prominent feature in electron-energy-loss spectra (EELS). The white lines of these elements have been studied and used to determine valance and coordination of atoms in various systems. Fe-O compounds with valence 2, 3 and mixed valence states, for example, have been carefully examined and characterized. However, in spite of the importance of iron sulfides in geochemistry and environmental science, the EELS data of these compounds are not available. Pyrite (FeS2) is widespread in hydrothermal ores, modern sediments, and sedimentary rocks deposited throughout the geologic record. The ferromagnetic iron sulfide greigite (Fe3S4) is another important compound. It has been recognized as a carrier of magnetic remanence in young sediments. Sedimentary greigite may be precipitated inorganically or biogenically by magnetotactic bacteria.

Substrates of fused silica or other refractory glasses are of interest for the fabrication of diamondbased electronic sensors (such as thermistors) and field-emitter arrays. For temperature-sensing applications, the diamond thin film layers must be deposited on thermally insulating substrates, in order to optimize the accuracy and dynamic response time of the device. Silica and silicate glasses are good insulators, providing a barrier to the heat flow out of the device and thereby allowing for optimized performance of temperature sensors. Also, fabrication of diamond field emitters on large area glass substrates is important for manufacture of field emission flat panel displays. Recently, it has been demonstrated that significant enhancement of diamond nucleation on Si02 substrates can be achieved by applying electrical bias to the substrate during its exposure to a microwave generated CH4/H2 plasma.

To investigate the nucleation mechanism of diamond on Si02 substrate, induced during the biasing pretreatment, several TEM techniques were used to characterize the films and the film/substrate interface.

Boron nitride thin films have been deposited on (100) oriented Si substrate by magnetically enhanced activated reactive evaporation technique. The build up of c-BN is normally accompanied by strong compressive stresses. When these stresses exceeds the strength of the adhesion forces at the interface, adhesion fails causing the destruction of the c-BN film. This has been one of the major limiting factors of using the c-BN films for many important industrial applications such as cutting tools and semiconductor devices.

In this experiment, the plasma immersion ion implantation has been applied to improve the adhesion of the film. The post ion implantation was conducted at several implantation energies and constant dose. The effect of ion implantation on the microstructures was investigated by Fourier Transform Infrared spectroscopy and Transmission Electron Microscopy.

Infrared characterization of c-BN film by FTIR (Fig.l) shows that the IR spectra of the specimens prepared at all energies but 72 kV have strong absorption band at 1080 cm-1 corresponding to cubic boron nitride.

Silicon carbide composites are known for high-temperature strength retention, creep resistance, high elastic modulus and light weight. Laminated matrix composites (LMC's) with a matrix of alternating layers of silicon carbide (SiC) and carbon (C) with carbon fiber reinforcements possess added toughness in addition to the desirable properties of SiC composites mentioned above. The improved toughness results from both the laminated matrix, which offers a tortuous path to crack propagation, and the energy expended in fiber debonding during fracture. Microstructural analyses of LMC's are necessary to help the processing effort to achieve structures with the desired properties. In this work, a preliminary examination of the microstructure of the laminated matrix composite is undertaken using TEM.

Specimens for TEM examination were prepared by cutting slices from a bulk sample of ∼ 1 mm thickness with a low-speed diamond saw. The slices were then ground to no less than 200 μm thickness to prevent the slices from breaking.

Aluminum nitride, translucent, calcia-sintered and hot pressed, with its superior thermal properties has applications in high performance electronic devices such as multichip modules. In these applications, A1N is exposed to high energy electromagnetic sources which could alter its properties; for example, upon UV irradiation, thermal conductivity drops and dielectric loss increases. These observations indicate that the UV altered properties are due to the presence of impurities. The early studies concentrated primarily on oxygen doped samples, which photodarken upon UV exposure; the role of other impurities was not considered.

In the current work, we consider the role of carbon in the microstructure of two very low oxygen content (< 0.3 wt %), carbon-containing samples, labeled B and E, for the ultimate purpose of 3 determining the mechanism by which carbon impurities affect the properties of A1N. Previous work on these samples correlated higher carbon content with a lower increase in the dielectric loss factor, after UV irradiation,

Magnetoresistance describes a phenomenon in which the electrical resistance of the material depends strongly on an externally applied magnetic field. Colossal magnetoresistance (CMR) was observed in a new class of oxides, (La,A)MnO3 (A = Ca, Sr, or Ba), and the Magnetoresistance ratio of ΔR/R(H)> -100,000% has been reported in epitaxially grown La0.67Ca0.33MnO3 films. The new types of intrinsic magnetoresistive oxides offer exciting possibilities for improved magnetic sensors, magnetoresistive read heads, and magnetoresistive random access memory (MRAM).

The CMR magnetic oxides have a perovskite-type crystal structure with ferromagnetic ordering in the a-b planes and antiferromagnetic ordering along the c-axis (Figure 1). The ferromagnetically ordered Mn-O layers of the a-b planes are isolated by a non-magnetic La(A)-O monolayer. This spin-coupling structure is intrinsic. La1-xAxMn03 compounds having the extreme values x = 0, 1 are neither ferromagnetic nor good electrical conductors; they are semiconductors. Only compounds with intermediate values of x are ferromagnetic,

A perovskite manganese oxide of Bi0.2Ca0.8MnO3 exhibits charge ordering of Mn3+ and Mn4+ ions upon cooling. This is an interesting phenomenon from both academic and practical viewpoints, since the charge ordering is accompanied by significant changes in both electric and magnetic properties of the oxide. Since a difference of scattering amplitudes between Mn3+ and Mn4+ is quite small, charge ordering can be observable as superlattice reflections due to the lattice strain caused by this ordering with an electron diffraction method. However, the background in an electron diffraction pattern, which is mainly caused by plasmon scattering, has hindered a precise investigation of the weak diffuse scattering. The purpose of the present work is to assess an efficiency of an omega-type energy-filter in detailed observations of the weak superlattice reflections associated with the charge ordering.

Specimens of Bi0.2Ca0.8MnO3 were prepared by a conventional ion-milling technique. The critical temperature of charge ordering (TCo) was determined to be 160K by resistivity and magnetization measurements.

Ferroelectric superlattices have been actively and intensively studied in recent years for their great scientific and technological interest. Superlattice containing Pb-based ferroelectric layers are important among ferroelectric superlattice systems, however, it is difficult to grow such superlattice due to the high volatility of Pb. Recently, great progress has been made in fabricating superlattice structure of PbZrO3/PbTiO3 by multi-ion-beam sputtering’ and molecular beam epitaxy (MBE). In this paper, we report the microstructural investigations of PbTiO3/SrTiO3 superlattice films, which were epitaxially grown on the SrTi03 substrate by MBE, using transmission electron microscopy (TEM).

[(PbTiO3)l0/(SrTiO3)l0]15 superlattice films were stacked on (100) SrTiO3 substrate alternately by MBE. Before growing the superlattice structure, a baffle layer including the 1000Å La-doped SrTi03 and the subsequent 500 Å PbTiO3 thin films was grown on the substrate. Above the PbTi03/SrTi03 superlattices, another PbTi03 thin film (1000 Å) was grown. Cross-section TEM specimens were prepared by standard methods.

Epitaxial thin film of SrRuO3 is very useful in device applications, due to its important electrical and magnetic properties. For example, (Pb,Zr)TiO3 ferroelectric capacitors with SrRuO3 thin film electrodes exhibit superior fatigue and leakage characteristics. Epitaxial SrRuO3 thin films grown on different substrates, such as on (001) SrTiO3 and (001) LaA1O3, have different magnetic properties, owing to the different microstructures in the film. Microstructures in epitaxial SrRuO3 thin films grown on (001) SrTiO3 have been studied in our previously work. In this paper, microstructure of epitaxial SrRu03 thin films grown on (001) LaA103 is reported.

SrRuO3 thin films on (001) LaA1O3 were deposited by 90° off-axis sputtering. For cross-section TEM studies the SrRuO3/LaA1O3 heterostructural samples were cut along the [100] direction of LaA103. The cut slides were glued face-to-face by joining the SrRu03 surfaces. Plan-view and cross-section TEM specimens were prepared by mechanical grinding, polishing and dimpling, followed by Ar-ion milling.

It is widely believed that the stress in the epitaxial thin films, caused by the lattice mismatch between the thin film and substrate, has a strong influence on the properties. For example, lattice strained epitaxial thin films of SrRu03 grown on (001) SrTiO3 demonstrated magnetic and electrical properties different from those in bulk materials.1 In this paper, we report the effect of strain relaxation of the thin film on microstructure by means of transmission electron microscopy (TEM).

SrRuO3 thin film on a vicinal (001) SrTiO3, with a miscut angle 0.9° and miscut direction 5.7° away from the in-plane [100] axis, was grown by 90° off-axis sputtering. Cross-section and plan-view TEM specimens were prepared following the procedure described in Ref. 2. TEM investigations were conducted in a Philips CM 12 microscope in the EMAL at the University of Michigan.

X-ray diffraction studies of the as-grown SrRu03 thin film using a four-circle diffractometer showed that the film consists of a single [ 110]-type domain structure.

The perovskite structure is based upon the mineral CaTiO3, which is a pseadocubic at room temperature. The ideal structure has a twelve fold coordinate A-site, and an octahedral coordinated B-site, and the face-centered position being oxygen. The perovskites have been of commercial interest for capacitors owing to their high dielectric constants. The crystal chemistry related to the perovskite based dielectrics multilayer capacitors (MLCs) is of interest in this paper. The MLCs with base metal internal electrodes such as copper and nickel have been studied for many years. To avoid oxidation of the nickel or copper electrodes during sintering, a reducing atmosphere is necessary. However, reduced firing causes two basic problems: an increasing of conductivity of the BaTiO3, dielectrics and limitation on reliability by the migration of oxygen vacancies. The solution for the first problem is to use acceptor dopants, such as MnO and more stable oxide additives, such as CaZrO3 to increase the resistivity of the dielectrics.

Achieving superplasticity in fine-grained ceramics is a potential method to lower energy costs associated with ceramic manufacturing via net shape forming. Superplasticity is intrinsic in 3-mol%- yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), and can be enhanced by addition of glass to form intergranular phases which are thought to both limit grain growth and promote grain boundary sliding during processing (sintering and hot isostatic pressing). This permits processing at lower temperatures. However, superplasticity has not been observed in 8-mol%-yttria-stabilized cubic zirconia (8Y-CSZ), ostensibly due to its larger grain size and high grain growth rates.3,4 As part of a larger study, high-spatial-resolution energy-dispersive X-ray spectrometry (EDS) has been performed on 3Y-TZP and 8Y-CSZ specimens doped with various glassy phases to characterize intergranular compositions.

Zirconia powders were mixed with glass to produce specimens having either 1 wt % lithiumaluminum- silicate, 1 wt % barium-silicate, or 1 wt % borosilicate. Some specimens were prepared without added glass.

EELS is a powerful analytical tool for exploring the local solid state environment in materials. There is an extensive literature on EELS analysis of the transition elements and light elements, yet few EELS data exist for heavy elements with multiple oxidation states. We report here on EELS studies of oxidation state influences on near-edge structure in cerium and uranium compounds.

All materials analyzed for this study were embedded in low viscosity epoxy and TEM specimens prepared using ultramicrotomy. The thin sections (∼50 nm thick) were analyzed using a JEOL 2010 (200kV) TEM operated with a LaB6 filament and equipped with a GAT AN 666 parallel EELS spectrometer. EELS data were collected in image mode at 105X magnification with a collection semi-angle of ∼ 100 milliradians at a dispersion of 0.1 eV/channel. The full width at half maximum of the raw (unprocessed) zero-loss peak was 0.7 eV. Peak positions were calibrated by applying a known voltage to a drift tube.

Metal-ceramic composites possess a wide range of applications due to an increased fracture toughness and strength compared to monolithic materials. A better understanding of the correlation between properties and microstructure of these materials requires a detailed analysis of the phases which form during processing. This can be accomplished by using various transmission electron microscopy (TEM) methods. In this study Nb based AI2O3 composites were investigated. The composites were prepared by pressureless sintering 2 of compacts of attrition milled AI2O3 and prealloyed Nb(Al) powder mixtures. The addition of 7 wt.% of Al to the Nb powder is supposed to assist in rapid and complete sintering of the material. The microstructure was studied in detail by conventional TEM using selected area diffraction (SAD). The chemistry and structure of the occurring phases, second phase particles and grain boundaries were analysed by analytical TEM and high resolution TEM (HRTEM).

Silicate glasses are the most common constituents of intergranular phases which can be found in liquid-phase sintered ceramics [1]. Silicates are known to influence the structure of ceramic interfaces which, in turn, frequently affect mechanical properties of ceramic materials [2]. In earlier studies of silicate glasses on single-crystal alumina Ramamurthy et al [3] and Mallamaci [4] showed that the morphology of dewetted glass films and the mechanism of devitrification depend on the crystallographic orientation of the substrate surface. In continuation of these studies, results are presented on the dewetting behavior of monticellite (CaMgSi04) in contact with the (OOl)-oriented surface of single-crystal MgO. Due to the simplicity of sample preparation and availability of 3- dimensional topographic information, Atomic Force Microscopy (AFM) was used for surface characterization. These AFM results are complemented by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) data on the chemical composition and the structure of the glass-substrate interface.