The limitation of the long-range order parameter and the necessity of the short-range order parameter for the thermodynamic description of Pb()O3-type perovskites are discussed. Based on the discussion, a statistical thermodynamic model that takes into account the configuration of the neighboring B-site ions (B′ and B″ cations) was developed. A pair-correlation approximation was used in the calculation of the configurational entropy and the long-range coulombic interaction energy between the nearest B-site ions. The theoretical calculations using Pb(Sc1/2Ta1/2)O3 (PST) and Pb(Sc1/2Nb1/2)O3 (PSN) systems indicate that the short-range order parameter persists over a wide range of temperatures examined (0–1800 K) and that there possibly occur consecutive long-range order-disorder transitions in the configuration of B-site cations. The possibility of the existence of short-range ordering above the long-range order-disorder transition temperature was also examined using the annealed PSN specimen as a typical example of Pb()O3-type perovskites.

The alignment and the formation of (Bi, Pb)2Sr2Ca2Cu3O10 inside an Ag sheath were investigated for tapes from four different precursor powders. Microstructural characterization along with in situ transmission x-ray diffraction experiments revealed that the kinetics depended strongly on the processing technique and the phase assemblage of the precursors. The alignment process was governed by the preferential grain growth of the Bi-cuprates along the a-b plane and the constraint applied by the sheath. The formation mechanism of (Bi, Pb)2Sr2Ca2Cu3O10 was either the intercalation or the nucleation and growth, depending on whether excessive liquid is adjacent to the platelets.

TiN films were deposited onto stellite 6B alloy (Co base) by the reactive magnetron sputter ion plating. As the substrate bias increases, TiN film changes from columnar structure to dense structure with great hardness and smooth surface due to densification and resputtering by ion bombardment. The content of oxygen and carbon impurities in the TiN film decreases greatly when the substrate bias is applied. The preferred orientation of the TiN films changes from (200) to (111) with decreasing N2/Ar ratio and from (200) to (111) and then (220) with increasing the substrate bias. The change of the preferred orientation is discussed in terms of surface energy and strain energy which are related to the impurity contents and the ion bombardment damage. The hardness of the TiN film increases with increasing compressive stress generated in the film by virtue of ion bombardment. It becomes as high as up to 3500 kgf/mm2 when an appropriate substrate bias is applied.

α–SiC (hexagonal) pressed powder targets were heated with a highly focused beam of CO2 laser radiation to temperatures in excess of 3200 °C in an oxygen- and water-free argon atmosphere. The argon pressure was maintained at greater than 100 atm to prevent vaporization of any liquid formed. This pressure was estimated to be several times greater than the total vapor pressure above a liquid solution of carbon and silicon. After a 30 s period at temperature, the heating was abruptly terminated. The 1 mm diameter region most affected on the surface of the SiC targets consisted of a central crater from which all SiC had been vaporized. The crater walls consisted of an amorphous carbon phase which acted as a matrix for fibrous graphite and granular silicon. Beyond the crater wall, the microstructure changed to that of various polytypes of hexagonal SiC, with the grains being equiaxed and smaller than those of the starting SiC powder, an indication that melting, followed by formation of a finer grain structure on abrupt cooling, may have occurred. Still farther from the crater, the microstructure was characterized by β-silicon (cubic) particles of spherical morphology and of larger size than the starting SiC powder, a response typical of solid state sintering. Even further from the crater, the structure was α-SiC, and the grain size was nearly the same as that of the starting material. The particles were lightly bonded together at points of contact between them, indicating only light sintering.

We find that the [Ni3.2nmPt1.6nm] × 15 and [Ni3.2nmPt0.8nm] × 15 multilayers are semicoherent and display a columnar morphology. From both the period of the moir’e fringes and the positions of the diffraction peaks in electronic (plan-view and crosssection geometries) and x-ray diffraction patterns, one deduces that the nickel is relaxed (at least in the error bars of all our measurements), whereas the platinum remains slightly strained (≈−1%). The interfaces are sharp; no intermixing takes place giving rise to neat contrasts in transmission electron microscopy (TEM) and to high intensities of the superlattice peaks in the growth direction in both diffraction techniques. The relaxation of the interfacial misfit occurs partially through misfit dislocations, partially through the strain of platinum. A quasiperiodic twinning occurs at the interfaces, the stacking fault which forms the twin being the most often located at the interface Pt/Ni, i.e., when a Pt layer begins to grow on the Ni layer. The simulation of the θ/2θ superlattice peak intensities takes into account the columnar microstructure. It shows that the roughness is predominantly at medium scale with a fluctuation of about 12.5% for Ni layers and negligible for Pt layers.

Mullite and mullite-like coatings on silicon carbide have been produced by a metal plasma immersion ion implantation and deposition (Mepiiid) technique based on two cathodic vacuum arc sources and concurrent pulse biasing of the substrate in an oxygen atmosphere. The deposition was carried out at oxygen partial pressures of between 0.66 and 3.33 Pa. The Al : Si ratio in the films varied from 1 : 1 to 8 : 1 and was controlled by varying the pulse duration of the separate plasma guns. High bias voltage was used early in the deposition process in order to produce atomic mixing at the film-substrate interface, while lower bias voltage was used later in the deposition; low ion energy allows control of the physical properties of the film as well as faster deposition rates. The as-deposited films were amorphous, and crystalline mullite was formed by subsequent annealing at 1100 °C for 2 h in air. Strong adhesion between the mullite and the SiC was achieved, in some cases exceeding the 70 MPa instrumental limit of our pull-tester.

The effect of excess bismuth on the ferroelectric properties of SrBi2Ta2O9 (SBT) thin films having a perovskite-like layered structure was investigated for excess bismuth contents ranging from 0% to 100%. For the first time, a limited solid solution of SBT and Bi2O3 was shown to exist when the amount of excess Bi was less than 50%. The formation of a solid solution enhanced the grain size and a-b plane orientation of the films, resulting in substantial improvement in the ferroelectric hysteresis properties of the films. On the other hand, when the amount of excess Bi exceeded 50%, Bi2O3 appeared as a second phase which led to high leakage current and poor ferroelectric hysteresis curves. 30–50% excess Bi content was found to be the optimum composition with respect to grain size, crystallographic orientation, and single phase formation. Within this range, SBT films exhibit low leakage current density (˜10−9 A/cm2) and maximum remanent polarization (2Pr ˜12 µC/cm2).

CaSi2 and CaSi have been investigated by Auger Valence Electron Spectroscopy (AVES). Some drastic differences of the Auger peak due to 3s states in the Si atoms were observed in the Si[2s, 2p, V] Auger spectra. The peak that arised from valence electron states in the Ca atoms was observed in the Ca[2p, 3p, V] Auger spectra for both Ca-silicides. This result suggests that the Ca–Si bonds are partially ionic. However, the number of the valence electrons in Ca atoms for CaSi was larger than that for CaSi2. This result implies that the part of homopolar bonds between the Si and Ca atoms in CaSi is stronger than that in CaSi2. Based on these results, it has been concluded that the change of the Si [2s, 2p,V] Auger spectra is associated with the difference of the part of homopolar bonds between the Si and Ca atoms.

The atomic force microscope (AFM) has been used to observe and characterize for the first time surface steps and grooves on the faces of Cr2O3 grains formed as an oxide scale on Ni−30Cr and Ni−30Cr−0.5Y alloys during high temperature oxidation. The very high spatial resolution of the AFM is required to characterize these features. We propose that these surface features, whose dimensions are in the range of nanometers and tens of nanometers, may be interpreted as evidence of highly localized plastic deformation of the oxide scale. The size and spacing of the steps and grooves are consistent with models of plastic deformation based on slip bands derived from dislocation climb or dislocation glide. Mechanical twinning and the models for stress-driven surface instability are also possibly responsible for some surface features. The addition of yttrium to the alloy seemed to enable enhanced plastic deformation of the scale. The strain corresponding to the observed features, estimated by simple models, could relax a significant part of oxide growth and thermal stresses.

New and modified mechanisms are proposed to account for detailed observations of carbon encapsulation of Fe, Ni, and Co nanocrystals. The mechanisms are based on aerosol and gas phase chemistry and on the catalytic effects of transition metals. Two parameters are found to qualitatively dominate production: the local-path carbon-to-metal ratio (LCM) and the global carbon-to-metal ratio (GCM). LCM's select which mechanisms are active along each pathway within the reactor. The GCM places bounds upon and determines the weighting between different LCM's and thus determines the distribution of different nanoscale products within the collected, macroscopic product. A two part processing parameter → mechanism → product map links the components. The generality of the model is discussed throughout with reference to related processes and the encapsulation of other materials.

Addition of a small amount of oxygen to the CH4 and H2 feed gas permits hot filament assisted chemical vapor deposition (HFCVD) of diamond at significantly lower filament and substrate temperatures. The former can be reduced to as low as 1400 °C and the latter to 450 °C. The amount of oxygen required is much lower than what has been used in most studies of the oxygen effect. For each CH4%, there is a narrow window in the O/C ratio, where diamond can be deposited at low temperature. This window shifts to higher O/C ratios as the CH4% increases and expands with increases in filament temperature. The effect of changing substrate and filament temperatures on growth rate and film quality are often not consistent with previous experiences with HFCVD of diamond. Increasing the filament temperature does not always improve the growth rate and film quality, and the non-diamond carbon content in the film is dramatically reduced at lower substrate temperatures. Optimum conditions were found that gave reasonable growth rates (∼0.5 μm/h) with high film quality at filament temperatures below 1750 °C and substrate temperatures below 600 °C. With these reductions in operating temperatures, power consumption can be significantly reduced and the filament lifetime extended indefinitely.

Multifilamentary (Bi, Pb)2Sr2Ca2Cu3Ox/Ag composites have been studied by a nondestructive magneto-optical imaging technique in order to determine the effect of filament architecture on the local magnetic flux distribution. The images reveal the homogeneity of the flux distribution in the upper layer filaments under magnetizing and demagnetizing conditions, and the alignment and morphology of these filaments in tapes with nine different composite structures. Certain types of filament arrangements led to homogeneous flux distributions, while other types caused localized inhomogeneities in the flux distribution. Nonuniform filament thickness also resulted in a highly inhomogeneous flux distribution. These results are useful in selecting optimal composite structures for power applications.

A classification scheme of Pb()O3-type perovskites with respect to the B-site order parameters was proposed based on the theoretical calculation of the short-range order parameter (σ) using the pair-correlation model. The calculated order parameters predict that a Pb()O3-type perovskite without any charge difference between B′ and B″ cations [e.g., Pb(Zr1/2Ti1/2)O3 (PZT)] is represented by a completely disordered state with the absence of a finite coherence length. On the other hand, a Pb()O3-type perovskite system having different ionic charges is characterized either by the short-range ordering with a nanoscale coherence length or by the macroscopic long-range ordering, depending on the magnitude of ionic charge difference between B′ and B″ ions. The normal ferroelectricity in Pb()O3-type complex perovskites was then correlated either with a completely disordered state (σ = 0) or with a perfectly ordered state (σ = 0), whereas the relaxor behavior was attributed to the nanoscale short-range ordering (0 < σ < 1) in the configuration of the B-site cations.

The adsorption of poly(vinyl butyral) (PVB) on NiCuZn ferrite powder in binary solvent systems of 1-butanol and toluene has been investigated. The adsorption isotherms of different PVB's on ferrite powder from various solvent mixtures follow closely the Langmuir monolayer types and can be explained by adsorption competition between solvents and PVB. A relatively poor solvent for PVB increases its adsorption on ferrite powder and thus improves the dispersion of the powder in the nonaqueous suspension. The adsorbance of PVB increases with increasing hydroxyl content in PVB suggesting that PVB is bonding strongly to the protruding surface hydroxyl groups on ferrite powder.

A complete study of the thermally activated demagnetization phenomenology taking place in multidomain barium hexaferrite sample is presented. From the irreversible magnetization dependence of the fluctuation field, it is concluded that a demagnetization mechanism independent of the magnetization value rules the reversal in samples having large enough particles. Differently from this, in a sample having a broad particle diameter distribution (and including a minority percentage of small, single domain particles), our results clearly indicate the occurrence of two different demagnetization processes. Also, it was observed that the activation volume, in all the samples, was of the same order of magnitude and clearly smaller than the particle volume.

Synthetic LaPO4, ScPO4, and crystalline natural zircon (ZrSiO4) from Mud Tanks, Australia were irradiated by 1.5 MeV Kr+ ions until complete amorphization occurred as indicated by the absence of electron-diffraction maxima. The resulting amorphous materials were subsequently irradiated by an 80 to 300 keV electron beam in the transmission electron microscope at temperatures between 130 and 800 K, and the resulting microstructural changes were monitored in situ. Thermal anneals in the range of 500 to 600 K were also conducted to compare the thermally induced microstructural development with that produced by the electron irradiations. Amorphous LaPO4 and ScPO4 annealed to form a randomly oriented polycrystalline assemblage of the same composition as the original material, but zircon recrystallized to ZrO2 (zirconia) + amorphous SiO2 for all beam energies and temperatures investigated. The rate of crystallization increased in the order: zircon, ScPO4, LaPO4. Submicrometer tracks of crystallites having a width equal to that of the electron beam could be “drawn” on the amorphous substrate. In contrast, thermal annealing resulted in epitaxial recrystallization from the thick edges of the TEM samples. Electron-irradiation-induced nucleation and growth in these materials can be explained by a combination of radiation-enhanced diffusion as a result of ionization processes and a strong thermodynamic driving force for crystallization. The structure of the amorphous orthophosphates may be less rigid than that of their silicate analogues because of the lower coordination across the PO4 tetrahedron, and thus a lower energy is required for reorientation and recrystallization. The more highly constrained monazite structure-type recovers at a lower electron dose than the zircon structure-type, consistent with recent models used to predict the crystalline-to-amorphous transition as a result of ion irradiation.

The coupling of calorimetric and microscopic techniques shows that the whole crystallization process for some Se100–x Tex (x = 10, 15) glassy alloys proceeds by two different mechanisms, which we call surface and bulk. These mechanisms are activated differently depending on the particular heating rate used and on the temperature of the isothermal heat treatment chosen. The nucleation frequencies and growth rates were determined from reflection polarized optical microscopy analysis, and a good agreement is found between these experimental results and predictions done by the classical nucleation and the normal growth theories. The apparent activation energy from the whole crystallization process which is obtained via differential scanning calorimetry is higher for Se85Te15 than for Se90Te10, and the relation with these values and those obtained from activation energies of nucleation and growth is established. A detailed discussion about the meaning of the different Avrami indexes found is presented.

A bulk sample of La0.6Mg0.4MnO3 has been prepared from coprecipitated carbonate precursor for the first time in this study. Structure analysis conducted by powder x-ray diffraction indicates that the sample is in the cubic perovskite phase. It shows a metal-insulator transition at 115 K (Tp) When applied to an external field, GMR effects are observed in the whole measured temperature range. The maximum negative MR value reaches as large as 480% at 105 K and 5 T. There may be two different mechanisms governing the GMR effects in the sample for the temperatures below and above Tp.

Microstructural and interfacial characterization of unidirectional SiC (SCS-6) fiber reinforced–reaction formed SiC (RFSC) composites has been carried out. Silicon–1.7 at.% molybdenum alloy was used as the melt infiltrant, instead of pure silicon, to reduce the activity of silicon in the melt as well as to reduce the amount of free silicon in the matrix. Electron microprobe analysis was used to evaluate the microstructure and phase distribution in these composites. The matrix is SiC with a bi-modal grain-size distribution and small amounts of MoSi2, silicon, and carbon. Fiber push-outs tests on these composites showed that a desirably low interfacial shear strength was achieved. The average debond shear stress at room temperature varied with specimen thickness from 29 to 64 MPa, with higher values observed for thinner specimens. Initial frictional sliding stresses showed little thickness dependence with values generally close to 30 MPa. Push-out test results showed very little change when the test temperature was increased to 800 °C from room temperature, indicating an absence of significant residual stresses in the composite.

The ac magnetic losses at power frequencies (60 Hz) were investigated for mono- and multifilament Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Oy (BSCCO-2223) tapes with similar Ic values at 77 K. The multifilament sample exhibited higher losses than the monofilament under the same conditions. Loss peaks are discussed in terms of intergranular, intragranular, and eddy current losses. Because of BSCCO's anisotropy, field orientation has a large effect on the magnitude of these peaks, even at relatively small angles. Losses for fields applied parallel to the c-axis of the textured BSCCO grains are larger by over an order of magnitude than those applied perpendicular.