We report on extended x-ray absorption fine structure (EXAFS) measurements for partially heat-treated gels in the lead zirconate titanate system (PZT). Self-consistent results obtained from the titanium and zirconium K-edges and the lead LIll-edge were used to determine bonding pathways between cations. For lead titantate (PT) and PZT gels, separate networks of predominantly Ti-O-Ti, Zr-O-Zr, and Pb-O-Pb linkages were observed. For lead zirconate (PZ) gels, both Zr-O-Pb and Zr-O-Zr linkages were observed. The results indicate heterogeneity at the molecular level. These findings are discussed in terms of the evolution of structure for PZT materials prepared by our sol-gel method.

A trilayer epitaxial structure of 3C-SiC/Si/3C-SiC was grown on Si(111) substrate by reactive magnetron sputtering. The layered structure consisted of a 300 nm thick Si layer sandwiched between two 250 nm thick 3C-SiC layers. Cross-sectional transmission electron microscopy (XTEM) showed that all layers were epitaxial to each other. The 3C-SiC layers contained stacking faults and double positioning domains with a high density in the second SiC layer. The Si layer showed the lowest density of planar faults, but developed growth facets. Observation was made of stacking faults propagating from 3C-SiC to Si layer as well as stacking faults originating at the termination of 3C-SiC double positioning boundaries into Si. The termination of Si stacking faults during growth of SiC is also reported.

Using ultrasonic-resonance spectroscopy (URS), we measured the elastic constant C and companion internal friction Q−1 of isotropic polycrystalline copper. The annealed material was 0.9999 pure with equiaxed heavily twinned grains averaging about 75 μm diameter. The URS method offers the principal advantage of point contact or loose coupling, thus there was no contribution from a transducer-specimen bond and only small contributions from transducers and fixture. A second advantage is one measurement for all elastic constants and all associated internal frictions. The C's agree with established values. The Q−1's are much lower than pulse-echo-method values. Comparison of measured Q−1 with the Koehler-Granato-Lücke model permits estimating an effective dislocation-loop length. Q−1 (shear) exceeds Q−1 (longitudinal) by a factor of about 1.5.

Diffusion in a regular solid solution was investigated. A thin plate of isotropic solid of constant surface molal fraction was considered. The regular solution is described by the parameter α. When α is positive, the attraction between unlike atoms is greater than the attraction between like atoms, and conversely. The depths of penetration and average molal fraction for a given period increase with increasing α. The separation of two curves for given α increase with increasing surface molal fraction. The diffusion coefficient is positive only if α is greater than −1/X(1 - X).

The Hg-Ba-Ca-Cu-O system phase diagram and the formation of HgBa2Can-1CunO2n+2+δ superconducting phases have been investigated by XRD (x-ray diffraction). The isothermal sections of the HgO-BaO-CuO system at 800 °C and the BaO-CaO-CuO system at 870 °C are presented. HgBa2Can-1CunO2n+2+δ superconducting phases are formed through the reactions of HgO with intermediate products Ba2CuO3 + BaCuO2 + CaO, BaCuO2 + CaO2, and BaCuO2 + Ca2CuO3 for n = 1, 2, and 3 phases, respectively.

We have reported here on low-temperature Raman scattering measurements on thin films of hydrogenated amorphous silicon (α-Si:H) alloys having different H contents. The Stoke's intensity, 77KITO, scattered at 77 K by the TO-phonon is found to be several times greater than its corresponding magnitude (300KITO) at 300 K. The ratio (77KITO/300KITO) is observed to vary exponentially with an increase in H concentration of the film. After eliminating various possible contributions to the scattering cross section, and therefore to the scattered intensity, this anomalous light scattering at 77 K is attributed to the possibility of polarizability modulation, which is believed to be caused due to a possible reduction in light-induced migration of H in α-Si:H and to the charge-carrier-induced enhancement of electron phonon coupling at 77 K.

The microstructural characteristics of melt-spun and heat-treated austenitic Fe−28Mn−8.6Al−0.5Mo−0.7W−0.5Nb−1.1C (in wt. %) alloys have been investigated by means of transmission electron microscopy. The melt-spun alloy contained fine austenitic cells and some intercelluar Nb(C, N) precipitates. Detailed observations revealed fine {100} modulations in the matrix of the cells, as well as a concomitant L′I2 atomic ordering arising from it. These observations indicate that the onset of decomposition of the initial austenite phase occurred during the rapid solidification process. Aging of the melt-spun alloy at 823–1173 K produced various microstructures, including a general precipitation of Nb(C, N) in the matrix. On isochronal annealing for 1 h, this matrix Nb(C, N) precipitation commenced at 1073 K with the formation of metastable coherent K-carbide (K′) near cell boundaries. On annealing at temperatures above 1123 K, only the Nb(C, N) precipitates were formed, on a fine scale, being accompanied by the formation of precipitate-free regions in the vicinity of cell and grain boundaries. Both intercellular and matrix Nb(C, N) precipitates obeyed a cube-to-cube orientation relationship with austenite. The general matrix precipitation of Nb(C, N) and formation of precipitate-free regions are discussed in terms of a vacancy (defect)-depletion effect. Finally, it was demonstrated that, by employing a double heat-treatment schedule of annealing at 1173 K followed by aging at 823 K, a novel microstructure consisting of fine dispersoids of Nb(C, N) carbo-nitride, distributed over the matrix of {100} modulated structure, could be produced.

Banded structures in combustion-synthesized products have been observed during unstable combustion synthesis. The formation of the banded structures is discussed in this article. It is noted that the band spacing was changed when several initial processing conditions were varied. Any change in the processing parameters that correspondingly caused more unstable combustion was observed to decrease the propagation velocity of the combustion front and increase the band spacing. The correlation of the band spacing and oscillatory frequency of the unstable oscillatory combustion with the propagation velocity was also discussed. From the results studied in this work, it is noted that the change of the band spacing can be used to infer the degree of the instability of the combustion front.

The microstructure of a microwave-densified silicon nitride based ceramic has been assessed in the as-sintered, post-sinter hot-isostatically pressed (HIPed) and annealed conditions. The grain size of the as-sintered material, which is a low substitution β′-Sialon, was significantly finer than observed in conventionally processed materials of similar composition. The as-sintered ceramic exhibits a reverse porosity gradient (with the highest porosity level at the surface) due to heat dissipation to the cooler surroundings during microwave processing. This also results in a higher β′ aspect ratio close to the surface arising from an increased glass viscosity (due to heat loss) and compositional change in this region during sintering. HIPing results in removal of all porosity from the sample core; however, a reduced porosity surface layer is retained. Significant β′-Sialon grain growth is also apparent after HIPing. A fine β′ grain structure was retained after annealing, with partial devitrification of the glassy grain boundary phase to β-Y2Si2O7.

Zirconium oxide dispersed in silica was synthesized by the cogelation of tetraethoxysilane and zirconium acetate. For the gelation, acid and basic media were used. The final zirconia concentration was around 6.7 wt. %. Differential thermal analysis, thermogravimetric analysis, as well as electron microscope techniques were used for the characterization of the samples. It was found that the stabilization of the crystalline phases depends on the preparation conditions and thermal treatments. Tetragonal and monoclinic ZrO2 phases were identified in basic preparations. However, in acidic samples only low-temperature tetragonal phase was identified.

Diamond-like carbon (DLC) films were deposited on (100) silicon wafers and silicon nitride balls by RF plasma-assisted chemical vapor deposition at a pressure of 700 mTorr and a substrate temperature of 360 K. The friction coefficient and the wear rates were measured using a pin-on-disk tribometer in 40% humid and dry air. Friction coefficients are near 0.05 in all cases measured. In dry air, the wear of silicon nitride and steel against DLC is below measurement capability because of a protecting DLC transfer layer, and wear of DLC is 2.5 ± 10−8 mm3/Nm against silicon nitride and 6.5 ± 10−9 mm3/Nm against steel. In humid air, the DLC transfer layer does not adhere to the solids, and wear of both bodies is larger. Unmeasurable wear is obtained when DLC slides against itself in humid air; the wear rate is 5 ± 10−9 mm3/Nm in dry air. These results are interpreted in terms of the properties of a friction-induced transformation of the surface layer of DLC.

Ba1−xSrxTiO3 (x = 0.9) ferroelectric ceramics were prepared successfully using a new wet technique and their structure and dielectric properties compared with those synthesized by the solid-state reaction method. The voltage dependence of the dielectric constant in the paraelectric phase was examined. It was found that the dielectric constants of these materials, prepared by both methods, exhibit large changes with applied voltage in the paraelectric phase. Tunability (the percentage change of the dielectric constant from its zero-bias value in the presence of a de-biasing electric field) was observed to exceed 30% at only 1.7 kV/cm at 77 K in the samples prepared by the solid-state reaction method. The tunability was found to decrease dramatically as the operating temperatures increased above the Curie point. These observations are interpreted in light of an existing phenomenological theory. The dependence of the dielectric constant in the paraelectric state upon a de-biasing electric field is also demonstrated as a potential method for the characterization of dielectric nonuniformities in ferroelectric ceramics.

Dielectric properties of polycrystalline BaTiO3 ceramics having grain sizes of 1 to 40 μm have been studied. Fine-grained ceramic BaTiO3 of 1 μm average grain size has 90°domains and has shown higher dielectric constant, lower ferroelectric transition temperature (Tc), and lower transition energy than coarser-grained material. 90°domain switching was preferentially produced in the fine-grained BaTiO3 as a result of abrasion. For the fine-grained BaTiO3, the dielectric constant decreased with one-dimensional pressure, whereas, for the coarse-grained material, the dielectric constant increased before decreasing with the pressure. The one-dimensional pressure resulted in increased Tc of both the fine- and coarse-grained BaTiO3, with the effect being the greatest for the coarse-grained material. The relationship between these results and internal stress, and the effect of external pressure imposed on internally stressed lattice, were discussed.

Palladium-supported alumina aerogels were prepared by two different supercritical drying methods. In one method, an alumina wet gel was dried under supercritical conditions of ethanol in an autoclave. In the other, the aerogel was supercritically dried by extracting ethanol using carbon dioxide in an extractor. The Pd-supported alumina aerogel prepared in the autoclave exhibited a high specific surface area of 112.8 m2/g after firing at 1200 °C for 5 h, while the other had a specific surface area of only 5.2 m2/g due to α-alumina transformation. Their catalytic properties for methane combustion were measured. The Pd-supported alumina aerogel prepared in the autoclave combusts methane perfectly at 50–60 °C lower temperature than the other. Palladium particles on the alumina aerogel prepared in the autoclave contained palladium oxide, while those prepared in the CO2 extractor contained only palladium metal.

A model for estimating the temperature rise in a laser-irradiated oxide target is developed and applied to laser-firing of sol-gel films on oxide substrates. The model incorporates a continuous-wave (CW) Gaussian laser beam translated across a sol-gel film on a semi-infinite substrate. Heat effects due to phase changes are assumed to be absent. In addition, the laser energy is assumed to be absorbed primarily in the substrate material (since many sol-gel films are much thinner than the absorption depth of typical laser wavelengths). The model also takes into account the temperature dependence of the thermal properties of the substrate. The predictions from the model are compared to experimental data from various laser firing experiments. The temperatures predicted by the model are shown to agree well with experimental results.

The electromechanical properties of sol-gel-derived ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT 53/47) thin layers deposited on silicon were determined as a function of field strength, measurement frequency, and total thickness. Both electrically induced strains (∊) and piezoelectric properties (d33) were characterized by interferometry. Dielectric spectroscopy and polarization switching (P-E) measurements were determined for comparative purposes. An asymmetry between forward and the reverse bias conditions in the ∊-E displacements was found for both five-layer deposited and nine-layer deposited structures. However, no asymmetry was observed in the P-E hysteresis characteristics. In addition, the electrically induced strains and the piezoelectric response were found to be dependent on measurement frequency. No significant frequency dependence was observed in the polarization or dielectric responses. The results are discussed in terms of a possible clamping effect on polarization switching.

α-SiC crystals were implanted with aluminum to a high dose at room temperature or 800 °C. Transmission electron microscopy showed that SiC was amorphized by room temperature implantation but remained crystalline after 800 °C implantation. Crystalline aluminum carbide was formed and aluminum redistribution took place in SiC implanted at 800 °C. Implanted and unimplanted crystals were oxidized in 1 atm flowing oxygen at 1300 °C. Amorphization led to accelerated oxidation of SiC. The oxidation resistance of SiC implanted at 800 °C was comparable with that of pure SiC. The oxidation layers formed on SiC implanted at both temperatures consisted of silica embedded with mullite precipitates. The phase formation during implantation and oxidation is consistent with thermodynamic predictions. The results from our current and earlier studies suggest that there exists an optimum range of implantation temperature, probably above 500 °C but below 800 °C, which preserves the substrate crystallinity and retains the high aluminum dosage, for the enhancement of oxidation resistance of SiC.

Boron-doped diamond films have been grown by the hot filament chemical vapor deposition process. The feed gas was a mixture of argon, bubbled through a solution of B2O3 in ethanol, and hydrogen. The highest growth rate was 0.7 μm/h. The boron concentration in the films depended on the concentration of B2O3 in the ethanol. The highest boron doping level, as measured by secondary ion mass spectroscopy, was 6300 atomic ppm. Raman spectroscopy and x-ray diffraction both confirmed the presence of crystalline diamond in the films. The frequency of the diamond Raman line decreased with increasing boron concentration. This shift may arise from an interaction of the charged carriers (holes) produced by the boron doping and the Raman-active optic phonon. The oxidation rates of doped and undoped films were measured by thermogravimetric analysis at 700 °C in flowing high purity oxygen. Films with a boron concentration of 6300 ppm oxidized at one-tenth the rate of undoped diamond. A layer of B2O3, detected on the surface of an oxidized B-doped film, is believed to act as a protective barrier that decreases the oxidation rate.

Diamond deposition on group VIII transition metals of Cr, Mn, Fe, Co, and Ni has been achieved by a multi-step chemical vapor deposition process consisting of (i) seeding the substrate with diamond powders, (ii) annealing the seeded substrate in hydrogen at high temperatures, and (iii) diamond nucleation and growth. It was found that high quality diamond can be grown on these substrates, and the often accompanied graphite formation, which has been the main obstacle in the deposition of diamond on these metal surfaces, can be largely suppressed by the above step-deposition procedure. This technique was further extended to the processes of depositing diamond on steels and Co-bonded WC materials.

New structural features observed in heat-treated vapor-grown carbon fibers (VGCF's), produced by the thermal decomposition of hydrocarbon vapor, are reported using image analysis of the lattice plane structure observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM lattice image of well-ordered graphite fibers (heat-treated VGCF's at 2800 °C) was treated by a two-dimensional fast Fourier transform, showing sharp bright spots associated with the 002 and 100 lattice planes. The heat-treated VGCF's consist of a polygonally shaped shell, and the long and short fringe structures in the TEM lattice image reflect the 002 and 100 lattice planes, respectively. From this analysis, new facts about the lattice structure are obtained visually and quantitatively. The 002 lattice planes remain and are highly parallel to each other along the fiber axis, maintaining a uniform interlayer spacing of 3.36 Å. The 100 lattice planes are observed to make several inclined angles with the 002 lattice planes relative to the plane normals, caused by the gliding of adjacent graphene layers. This work visually demonstrates coexistence of the graphitic stacking, as well as the gliding of the adjacent graphene layers, with a gliding angle of about 3–20°. These glide planes are one of the dominant stacking defects in heat-treated VGCF's. On the other hand, turbostratic structural evidence was suggested by AFM observations. The structural model of coexisting graphitic, glide, and turbostratic structures is proposed as a transitional stage to perfect three-dimensional stacking in the graphitization process. These structural features could also occur in common carbons and in carbon nanotubes.