10B doped diamond films grown by hot filament chemical vapor deposition were neutron irradiated at moderately high fluence levels. The as-irradiated and annealed samples, along with an unirradiated sample, were analyzed using Raman spectroscopy and x-ray diffraction. It was found that a non-diamond amorphous phase was formed on irradiation. This phase transformed back to diamond on annealing. No graphite formation was observed. A comparison with nanodiamond powder was made. A similarity between irradiated diamond films and nanocrystalline diamond powder is discussed.

The nature of amorphous carbon has been explored by molecular mechanics by examining the structures of species such as C84Hx and C150Hx, wherein the percentage of sp3 carbons is progressively increased in a graphitic network. The nature of diamond-like carbon has been similarly investigated by examining the structures of C84Hx and C102Hx where the percentage of sp2 carbons is varied in an sp3 network. The dependence of the average coordination number as well as the sp3/sp2 atom ratio on the atom fraction of hydrogen has been investigated in light of the random covalent network model.

The possibility of an autostoichiometric vapor deposition is explored. Heterometal-organic complexes such as double alkoxides are potential candidate precursors for such deposition. Two reaction schemes, the hydrolysis-assisted pyrolysis and the hydrolysis-polycondensation of double alkoxides, are identified to be autostoichiometric reactions. A simple low-pressure apparatus is suggested for autostoichiometric vapor deposition. Mass-flow analysis allows for the identification of a nonstoichiometry factor K which can be used as a quantitative measure of the precursor's autostoichiometric capability.

An autostoichiometric vapor deposition method is implemented to achieve deposition of stoichiometric LiTaO3 using LiTa(OButn)6 precursor. Precisely stoichiometric LiTaO3 can be grown by this method. A simple low pressure reactor is used to facilitate the autostoichiometric vapor deposition through hydrolysis polycondensation of double alkoxides in the vapor phase. Typical deposition and annealing conditions are described. X-ray diffraction, SEM, and compositional analyses are performed on the films grown on fused silica, Pt, (100) sapphire, and LiNbO3(001). Rocking curve measurements indicated excellent epitaxial growth of LiTaO3 on (100) sapphire. Compositional analysis by measurement of lattice parameters confirmed that the present method can produce high quality stoichiometric LiTaO3. The nonstoichiometry factor for LiTa(OButn)6 is negligible. Mass spectrometric study of the precursor compound LiTa(OButn)6 suggests that the volatile species is Li2Ta2(OButn)12.

Composed of packed nanophase nodules in which the carbon atoms are linked with the tetrahedral bonding of diamond, laser plasma films are deposited in vacuum onto almost any substrate by condensing carbon ions carrying keV energies. These multiply charged ions are obtained from the laser ablation of graphite at intensities in excess of 1011 W cm−2. The high energy of condensation provides both for the chemical bonding of such films to a wide variety of substrates and for low values of residual compressive stress. Coatings of 2–5 μm thicknesses have extended lifetimes of important optical materials against the erosive wear from high-speed particles and droplets by factors of tens to thousands. In this work, the optical properties of these films at infrared (IR) wavelengths were studied. Transmission spectra of several freestanding films on silicon frames were measured. Using a model considering rough surface scattering and free carrier absorption, satisfactory fits to these transmission spectra were obtained and from them the optical parameters were extracted. The characterization studies performed in this work indicated a great potential for the laser-deposited nanophase diamond films in optical applications.

Diamond windows were heated at 700-900 °C in air for short times to better define the limits of application at high temperature. The infrared (IR) transmission of polished chemical vapor deposition (CVD) diamond windows was reduced after heating in a furnace at 800 °C for 75 s, while heating at 700 °C for 75 s produced little change. The 800 °C heating caused increased visible light scatter, and increased scatter appears to be mainly responsible for the reduced IR transmission. The forward scatter at 10.6 μm for the CVD diamond samples was 0.8% before heating, 2.8% after heating at 800 °C for 75 s, and 6.2% after heating at 800 °C for 255 s. Single crystal (110) type IIa diamond exhibited little change in IR transmission when heated at 800 °C in air for 255 s, while heating for 555 s at 800 °C caused a significant drop in IR transmittance (6-12%). A slight drop in IR transmittance (1-5%) occurred for a type IIa diamond when heated at 900 °C for 45 s. The etched surfaces were characterized by differential interference contrast optical microscopy, scanning electron microscopy, and Talystep surface profiles. Etched features are concentrated at grain boundaries (for the CVD samples) and at sites with residual damage from mechanical polishing that could not be seen before the heat treatment. Deep etch pits formed at grain boundaries that extend into the bulk of samples.

Film growth and microstructural evolution were investigated for sol-gel derived LiNbO3 thin films deposited on lattice-matched single-crystal substrates. Epitaxial LiNbO3 films of about 100 nm nominal thickness were prepared by spin coating a solution of the lithium niobium ethoxide on sapphire (0001) substrates and annealing at 400 °C or 700 °C in a humidified oxygen atmosphere. These films exhibited an epitaxial relationship with the substrate of the type LiNbO3 (0001) || α-Al2O3 (0001) and LiNbO3 [100] || α-Al2O3 [100] as determined by x-ray pole figure analysis. Transmission electron microscopy indicated the epitaxial films annealed at 400 °C consisted of slightly misoriented ∼5 nm subgrains and of numerous ∼10 nm enclosed pores. The microstructure and orientation development of these films was consistent with a heteroepitaxial nucleation and growth mechanism, in which epitaxial nuclei form at the substrate surface and grow upward into an amorphous and porous intermediate film: Epitaxial films annealed at 700 °C contained larger 150-200 nm subgrains and pinholes. Misorientations between adjacent subgrains appeared to be significantly smaller in films annealed at 700 °C than those in films annealed at 400 °C. Hydrolysis of the alkoxide precursor solution prior to spin coating promoted the development of polycrystalline films on single-crystal sapphire substrates. Infrared spectra and thermal analysis indicated that, independent of the degree of the solution hydrolysis, nucleation of LiNbO3 was immediately preceded by decomposition of an amorphous carbonate intermediate phase.

This paper extends the concepts that were developed to explain the structural rearrangement of the wurtzite AlN lattice due to incorporation of small amounts of oxygen, and to directly use them to assist in understanding the polytypoid structures. Conventional and high-resolution transmission electron microscopy, specific electron diffraction experiments, and atomistic computer simulations have been used to investigate the structural nature of the polytypoids. The experimental observations provide compelling evidence that polytypoid structures are not arrays of stacking faults, but are rather arrays of inversion domain boundaries (IDB's). A new model for the polytypoid structure is proposed with the basic repeat structural unit consisting of a planar IDB-P and a corrugated IDB. This model shares common structural elements with the model proposed by Thompson, even though in his model the polytypoids were described as consisting of stacking faults. Small additions (≃ 1000 ppm) of silicon were observed to have a dramatic effect on the polytypoid structure. First, it appears that the addition of Si causes the creation of a new variant of the planar IDB (termed IDB-P'), different from the IDB-P defect observed in the AlN-Al2O3 polytypoids; second, the addition of Si influences the structure of the corrugated IDB, such that it appears to become planar.

27Al and 31P NMR spectroscopic data are presented for the tridymite polymorph of AlPO4 (AlPO4−1) through its structural phase transition at about 80 °C. The RT 27Al and 31P spectra of AlPO4−t both contain doublets of broad peaks, indicating two well-separated groups of sites in the RT structure with mean Al-O-P bond angles per tetrahedron of ∼ 147.8°and 153.1°(±1). With increasing temperature, the doublets remain the same up to about 74 °C, where the relative intensities of the two peaks start to change. The peak corresponding to smaller Al-O-P bond angles disappears, and above ∼88 °C the 27Al and 31P spectra contain single symmetrical peaks, corresponding to a mean Al-O-P bond angle of 153.4°. This bond angle increases gradually with increasing temperature to 153.7°at ∼150 °C and remains constant to about 500 °C. 27Al quadrupole echo experiments suggests that the 27Al nuclear quadrupole coupling constant (QCC) is small and decreases with increasing temperature. QCC remains nonzero in the high temperature phase of AlPO4−t, consistent with the previously proposed 3m local symmetry of Al in the high-temperature structure.

Mullite and zirconia-mullite ceramics have been prepared by coating alumina/zirconia particles with an amorphous silica layer. The effect of composition change of the amorphous silica layer by adding B2O3 was investigated. For the zirconia-free compositions, the addition of B2O3 remarkably accelerates the kinetics of the crystallization of the amorphous coating layer, the viscous sintering, and the mullitization. For the zirconia-containing ceramics, the addition of B2O3 enhanced the viscous sintering kinetics and delayed the decomposition of the transient zircon phase and the subsequent t- to m ZrO2 transition, thus resulting in a higher ratio of t- to m-ZrO2. The B2O3-containing zirconia-mullite composites exhibit the same level of fracture toughness (Kic) as the B2O3-free zirconia-mullite composites.

Nanocrystalline TiB2 is prepared by reaction of NaBH4 and TiCl4. The initial solution-phase reaction affords an amorphous precursor powder from which 5-100 nm TiB2 crystallites are obtained upon annealing at 900-1100 °C. Crystallite sizes depend on the annealing temperature and other processing parameters. Crystallite morphology is size dependent; crystallites smaller than 12-15 nm are cuboidal, whereas crystallites larger than 12-15 nm are hexagonal platelets. The procedure affords gram quantities of the smallest available TiB2 nanocrystallites.

Hertzian contact damage in as-fired, peak-aged, and over-aged Mg-PSZ is studied, in single-cycle and multiple-cycle loading. Indentation stress-strain curves reveal a monotonically increasing quasi-plasticity component in the contact deformation with increasing aging time. A bonded-interface technique is used to obtain surface and subsurface views of the damage zones beneath the spherical indenter. Analytical techniques, including optical and scanning electron microscopy, acoustic emission, Raman spectroscopy, and thermal wave imaging, are used to characterize the damage. The damage patterns are fundamentally different in the three aging states: microfracture dominated in as-fired; tetragonal-monoclinic phase-transformation-dominated in peak-aged; monoclinic-phase twinning-dominated in over-aged. The damage accumulates with increasing number of cycles, most strongly in the as-fired state. It also increases with increasing test duration in the as-fired and over-aged states, but not perceptibly in the peak-aged. The results imply predominantly mechanical fatigue effects, augmented by a chemical component in the as-fired and over-aged states. Broader implications in relation to the susceptibilities of zirconia ceramics to fatigue degradation in concentrated stress configurations, with special relevance to the evolution of flaws at the microstructural level, are considered.

Thin amorphous films of ceramic capacitor materials were successfully deposited using sol-gel chemistry onto titanium wire using a continuous, computer-controlled process. By repeatedly depositing and calcining very thin layers of material, smooth and even coats can be produced. Surface analyses revealed the layered nature of these thin coats, as well as the amorphous nature of the ceramic. The electrical properties of the better coatings, all composed of niobrium, bismuth, and zinc oxides, were then evaluated.

Thin films of Pb(Mg,Zn)1/3Nb2/3O3 (PMZN) were fabricated by spin casting the partially hydrolyzed Pb-Mg-Zn-Nb-O complex alkoxide sols on (111) Pt-coated MgO(100) planes. Analysis of the isothermal transformation data indicated that the growth of perovskite grains from the pyrochlore matrix is a diffusion-controlled process with an initial fast nucleation. The effect of water concentration in the sol on the preferential orientation of perovskite grains in the corresponding thin film was examined. A strong preferential orientation of (100) perovskite was obtained in the PMZN thin film derived from the sol having a molar ratio of H2O to total metal alkoxides (Rw) of 2. A small-angle x-ray scattering (SAXS) experiment in the Porod region indicated that weakly branched precursor systems led to highly (100)-oriented perovskite grains after thin-film formation. The pyroelectric coefficient and the corresponding figure-of-merit were controlled by suitably varying the degree of preferential orientation during the fabrication of thin films.

The synthesis of tungsten silicides by self-propagating combustion has been successfully accomplished under the influence of an electric field. Materials with starting composition ranging from 6 to 30 wt. % Si were investigated by the method of field-activated combustion synthesis (FACS). A threshold field value was required to initiate a self-sustaining wave; the threshold value depended on composition. It was shown that the level of the applied field can influence the mechanism of silicide formation. The silicide W5Si3 could be formed only at relatively high field values while WSi2 can be formed at any field. The effect of the field on the silicide formation is discussed in terms of its role in liquid phase formation.

Cu2+-containing SiO2 and Al2O5 · 9SiO2 glasses were prepared by the sol-gel method and heated under reducing conditions to precipitate small-sized Cu and Cu2O erystals. Cu2+ ions incorporated in SiO2 glass were reduced by heating in N2 to precipitate Cu2O and in H2 to precipitate Cu microcrystals with diameters of about 5 to 15 nm. Microcrystalline Cu-precipitated glass showed an optical absorption band at 560 nm and its third-order nonlinear susceptibility was 1.25 × 10−10 esu, which originated from the enhancement by the surface plasmon resonance of Cu particles. In contrast, Cu2+ ions incorporated in Al2O3 · 9SiO2 glass remained unchanged after heating in the reducing gas atmospheres.

Infrared (IR) and UV-spectra have been obtained for pure and Fe3+ doped acrylonitrile-butadiene-styrene (ABS) terpolymer. IR study revealed the appearance of a new band at about 380 cm−1, and a change of the shape and the intensity of the band at 1450–1500 cm−1 and 2240 cm−1 indicates the structural change on blending due to the τ-complexes and the complexes of the functional groups with Fe3+ forming an ion-coordination polymer. The UV spectrum confirms this result. The optical energy for pure and Fe3+-doped ABS is found to be 3.75 eV and 3.55 eV, respectively. The dc and ac electrical conductivities have been investigated. The apparent conductivity of high Fe3+-doped ABS at the ambient temperature is about six orders of magnitude greater than that of the undoped film. The activation energy drastically decreases as the wt. % of FeCl3 increases. The enhanced conductivity in the complex film may be attributed to the capacity of the dopant to give additional charge carriers. Transport of charge carriers will occur by hopping of charge carriers between close neighbors across the intervening dielectric, probably via a thermally activated process.

A series of polysilanes was prepared by the alkali metal dechlorination of chlorosilane monomers, in which the overall functionality, F, of the reaction was varied. Starting monomers of functionality f = 2.0 and 3.0 were reacted together in various proportions to achieve values of F of 2.2, 2.35, and 2.5. In addition to varying the functionality of the reaction, three different difunctional monomers, dimethyldichlorosilane (DMDCS), diphenyldichlorosilane (DPDCS), and methylphenyldichlorosilane (MPDCS), and two trifunctional monomers, phenyltrichlorosilane (PTCS) and ethyltrichlorosilane (ETCS), were used. The effect of these changes on the yields of the polysilanes was determined, and the products were investigated by the use of thermogravimetry (TG), gel permeation chromatography (GPC), and thermomechanical analysis (TMA). The ability to spin a polysilane fiber was also assessed.

A moving screw dislocation near a surface crack was investigated using dislocation modeling. Motion directions parallel (x direction) and perpendicular (y direction) to the crack surface were considered. Due to the free surface, the net Burgers vector inside the crack is zero. After obtaining the dislocation distribution in the crack, we calculated the stress field in the medium. Relative to a static screw dislocation, the magnitude of σyz due to the moving screw dislocation decreases with increasing velocity Vx. Generally, the effect of dislocation shielding on fracture is reduced if the velocity Vx increases. The magnitude of the image force of the dislocation also decreases with increasing velocity Vx. The effect of velocity along the y direction on the stress intensity factor and image force has the opposite trend to that along the x direction. The present result can reduce to a moving dislocation near a semi-infinite crack and a static dislocation near a surface crack.

In this brief letter we want to comment on several statements published recently in the Journal of Materials Research by our former co-workers Kellett and James (KJ) in the paper entitled “Ion beam sputter deposition of YBa2Cu3O7−δ thin films”.