Long period polytypoid structures observed along the pseudobinary Al2O3-AlN composition join at a composition of 95 mol% A1N have been investigated by convergent beam electron diffraction and lattice imaging. Two new long period structures, 32H (Ramsdell notation) and 16H with c-periodicities of 8.3 nm and 4.07 nm respectively, have been independently identified by these two techniques. However, the 32H polytypoid was sometimes found to be intergrown with faulted 27R long period structure of periodicity 7.2 nm. Further, it has been shown that the 32H polytypoid is stabilized by local compositional fluctuations during the sintering process.

Surface steps have been observed on low-index planes of alpha-alumina and spinel. The steps were produced by annealing both bulk and perforated thin foil single crystals. A comparative study of bright-field TEM and dark-field REM of the same crystals makes it possible to construct models for the surface structure. Many faceted steps can be observed on the (0001), {0112}, {1010} and {1120} surfaces of alpha-alumina and on the {100} surface of spinel. A detailed study of step faceting and step facet movement during reheating is presented.

The atomic structures of a number of <001> high-angle tilt grain boundaries in NiO have been studied by high-resolution electron microscopy (HREM). Crystal 1inity is always maintained right up to the grain boundary (GB). Grain boundary planes bounded by a (100)-plane are preferred, however symmetrical facets are also found at each misorientation. A tendency to match atomic planes across the GB is not only observed in symmetrical, but also in asymmetrical GBs. Structural units can be clearly recognized in symmetrical GBs. Contrast differences suggest that a multiplicity of structural units exists for some GB configurations. Frequently symmetric GBs also show deviations from mirror symmetry. Multislice simultations indicate that the image contrast associated with HREM GB images is not particularly sensitive to GB relaxation.

The substitution of divalent metal ions for γ(+3) in γCrO3 results in a charge compensating transition of Cr(+3) to Cr(+4) and the formation of small polarons as charge carriers. The experimentally measured electrical conductivity, σ, and Seebeck coefficient, S, exhibit behavior consistent with a theoretical model developed for small polaron transport in these narrow-band semiconductors. The small polaron transport is a thermally-activated process with a measured activation energy, E, of about 0.18 to 0.25 eV in these materials. Both σ and S increase with temperature and show a near linear dependence on dopant concentration and a strong dependence on dopant (ionic) size. Analysis of the results in terms of the model indicates that Ca is much more effective in polaron formation than any of the other dopants in γCrO3; this is due to the similar ionic size of Ca(+2) and γ(+3) which minimizes the lattice distortion from substitution.

Defect studies at high defect content in transition metal monoxides allow for the conduction mechanisms to be established and the nature of defect interactions to be studied. Conductivity and thermopower results in p-type, highly defective MnO are reported and analyzed with a combination of point defects and clusters. A high pressure oxygen apparatus to achieve defect contents up to 5 percent in CoO has been designed and constructed.

The effect of CaO substitutions (between 1 and 10% (CaO)2/Li2O) on the transport and physical properties of two fast ion conducting lithium borate glass systems (37.3 mol % Li20, 62.7 mol % Li2O3 and 50 mol % Li2O, 50 mol % Li2O, 50 mol % B2O3) are investigated. Measurements of electrical conductivity, density and glass transition temperature are reported. The influence of strain effects on carrier mobility is examined. Measurements of electrical conductivity and molar volume are extended to a K2O·2B2O3 glass and compared with existing data for corresponding lithium and sodium diborate glasses.

A new method for thermal expansion measurements is described. The technique is based on rotation of a laser beam reflected from a probe bar caused by uneven thermal expansions of sample and reference rods. At a distance, the reflected gaussian laser beam is observed with a small photodetector (much smaller than the beam cross-section). The measurement of minute beam position change thus results in related low thermal expansion measurement capability. Experimental arrangement and the sensitivity are described. Some results are also reported.

The formation of nickel-aluminate spinel during the reaction between nickel oxide and alumina has been studied by a new approach which utilizes a thin-film substrate of alumina. It is found that the spinel grows in either near- or exact-topotactic alignment along the edges of the thin-film substrate. It also grows on and into the surface of the substrate, but the deviation from exact topotaxy then tends to be larger. The topotactic relationship is such that the (0001) of the alumina is parallel or nearly parallel to the {111} planes of the spinel with <1100> parallel to <110>. A second orientation relatioship is found where the {1120} of the alumina is parallel or nearly parallel to the {111} planes of the spinel; <1100> is again parallel to <110>. First order twin boundaries are found to be common in the spinel particles which have grown on the edge of the thin alumina substrate. Direct observation of the change in the orientation of the spinel twins with respect to the alumina substrate after reannealing is reported. The morphology of the various types of spinel particles is discussed briefly.

The reliability of mlcrofocus x-rad1ogrphy for detecting Internal voids 1n structural ceramic test specimens was statistically evaluated. The micro-focus system was operated in the projection mode using low x-ray photon energies (≤;20 keV) and a 10 μm focal spot. The statistics were developed for Implanted Internal voids 1n green and sintered silicon carbide and silicon nitride test specimens. These statistics were compared with previously-obtained statistics for implanted surface voids in similar specimens. Statistical results are given as probability-of-detection curves at a 95 percent confidence level for voids ranging in size from 20 to 528 μm in diameter.

The clean room processing, firing and crystal growth techniques required to produce high-purity Al2O3 crystals and bicrystals with [2110] tilt boundaries near low Σ misorientations are described. The chemical analysis requirements for high-purity ceramic materials are discussed. The boundary characteristics of the θ=33.2°, near Σ = 11, misorientation and the applicability of the CSL model to describe the observed facet planes is determined. The periodicity of the dislocations present in the boundary is 21 nm. STEM analysis of the grain boundary region indicates no second phase or detectable impurity concentrations. The importance of gra in boundary structure investigations in high-purity materials and of chemically well-characterized boundaries is discussed.

Atomistic lattice simulations are reported of the segregation of yttrium at the {0001}, {1010} and {0112} surfaces and magnesium at the {0001} surface of α-Al2O3. Equilibrium coverages are deduced from the calculated enthalpies of segregation on the basis of a non-Arrhenius isotherm. For magnesium the calculated enthalpy of segregation at low coverage, ∼158 kJ mole−1, is in good agreement with a measured value of ∼146 kJ mole−1 reported recently.

We calculate energies and entropies of a variety of defect processes using the SHEOL code. It is shown that only the Co2+ ion is responsible for cation migration, thus explaining the experimental result that the migration energy is independent of defect charge.

It is demonstrated that microscopic point defects can be created in amorphous silica using pulsed ultraviolet irradiation (λ = 248 nm) at energy densities ∼ 100 times less than those normally estimated to lead to damage creation. Identification of the physical character of the defects has been made using electron spin resonance spectroscopy and electrical measurement techniques. Continued irradiation of the SiO2 is found to lead to photoablation. Results obtained for bulk dry SiO2, thermal SiO2 and vacuum deposited SiOx are presented. The important role of non-stoichiometry (defect structure) in the process of photoablation is clearly manifested by comparison of the results obtained for the different types of SiO2. Possible physical mechanisms involved are discussed.

We have studied mixing of metal overlayers (Ni, Cr, Ti, W, Ta, Zr, Cu) on insulators (SiC, Si3N4, Al2O3, SiO2) after ion beam irradiation, rapid thermal annealing, and pulsed laser irradiation. The nature and amount of mixing varies from stoichiometric to continuous, to ballistic, to no mixing at all. For a given system, the amount of mixing was found to increase with increasing substrate temperature. The enhanced mixing with increasing substrate temperature is correlated with concomitant free energy associated with the reactions. Certain systems such as Cu on Al2O3 do not exhibit mixing, but rearrangement within a few atomic layers at the interface results in enhanced adhesion and no aggregation upon annealing at moderate temperatures.

The effect of small coverages of Cu evaporated in ultra-high vacuum (UHV) on A12O3 (0001) surfaces has been investigated by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). These surfaces were cleaned either by annealing at 1000°C in O2 or by Ar sputtering. They differ both in their initial state and their interaction with Cu. The XPS spectra from as-deposited Cu on sputtered samples exhibit small shifts in the energy location of the various peaks as compared to those from a Cu standard. Annealing the Cu/sputtered A12O3 structure at 500°C produces a shoulder on the Cu 3d peak as well as a new Cu (L3 M4.5 M4.5) Auger feature. Neither of these effects are observed after similar treatment of the Cu/annealed A12O3 structure. An influence of this different bonding situation on the Cu-sapphire interfacial energy is observed.

The crystallization of amorphous surface layers produced by ion implantation of single-crystal α-Al2O3 and CaTiO3 are discussed. During annealing, amorphous A12O3 converts first to the α-phase. The crystallized γ then transforms to the a-phase by the motion of a well-defined planar interface. The temperature dependence of the velocity of the γ/α interface has been measured and is characterized by an activation energy of ∼3.6 eV. In CaTiO3, crystallization of the amorphous phase takes place by solid-phase epitaxy. The velocity of the amorphous/crystal interface is characterized by an activation energy of 1.3 eV.

CO2 Laser heating of c-axis sapphire filaments was used in a low pressure flow reactor in order to study evaporation and chlorination of single crystal and liquid aluminas. Reacted specimens were examined by scanning electron microscopy (SEM) to monitor the evolution of facets and other surface structures with reaction conditions.

An increase of the incident energy on a laser heated sapphire filament at the melting point does not result in complete melting, because the semi-transparent melt layer that forms has a higher effective emittance than the solid. This technique allows simultaneous reactivity study of liquid and single crystal aluminas at the melting point, as well as study of reactions of single crystal alumina at lower temperatures.

Sapphire specimens develop a hexagonal prism shape after reaction with chlorine containing gases whereas evaporation does not change the initially cylindrical specimen shape.

The primary structural characteristic of the 0.025 cm as-received sapphire specimens from Tyco is the presence of ∼1μm voids that are produced during the growth of the crystal. These voids form conical arrays 20–30μm apart along the filament axis. Specimens reacted with chlorine containing gases below ∼1900K exhibit surface structures which form arrays with the same size and pattern as the voids in the as-received specimens.

Growth conditions are described for producing high quality crystalline films of CaF2 on (100) and (111) GaAs and LaF3, CeF3 and NdF3 on (111) Si. Rutherford backscattering/channeling, low temperature (<2K) photolumin-escence and Raman scattering are used as diagnostic techniques to probe the crystalline quality of the films and the stress/disorder induced at the film-substrate interface due to lattice mismatch.

Modern varistors are made of polycrystalline ZnO, doped to create Schottky-like barriers at the grain boundaries. To allow the study of tailored single barrier junctions, we have implanted ZnO crystals with Bi, Sb and transition metals. The electrical properties and the distribution of Bi and Sb were measured in the implanted crystals as a function of annealing temperature. After implantation and before heating, no barriers can be observed. After heating to 600–800°C, a high voltage (insulating) barrier is created. Heating to above 1000°C produces a 2-1/2 Volt barrier with high nonlinearity. The temperatures at which these barriers appear correspond, respectively, to temperatures at which motion of Sb and Bi first can be observed by ion backscattering techniques, and at which these elements diffuse freely.

TiOx thin films were fabricated by means of a reactive sputtering technique in an rf triode sputtering-deposition unit. The deposition rate was studied in detail. A ‘phase diagram’ of TiOx was determined. XPS study showed the formation of a Ti02 surface layer on TiOx thin films. Oxygen was removed by the Ar+ bombardment on Ti02 to yield Ti203.