A Zr-modified polycarbosilane has been obtained reacting a zirconium alkoxide with a polycarbosilane. This new preceramic polymer has been nitridated in flowing ammonia up to 1000 °C. The conversion process of the polymer precursor to the Si–N–Zr–O ceramic has been followed mainly by FT-IR, XRD, and TEM investigations. The formation of the Si–N–Si network starts at 600 °C. At 1000 °C the system can be described as an amorphous silicon nitride ceramic in which very fine zirconia-based particles are dispersed. Increasing the temperature to 1300 °C results in the crystallization of t-ZrO2 microcrystals (35 Å in size). At higher temperatures the crystallization of the silicon nitride matrix into β–Si3N4 has been observed.

Very small NiFe2O4 particles between 1 and 4 nm in size have been observed in an Fe-doped NiO sample quenched during early stages of spinel precipitation. The differences between the crystal structure of NiFe2O4 and NiO made it possible to use three different TEM imaging techniques to observe these very small particles. These very small particles are distributed throughout the volume of the sample and hence were not produced by specimen preparation. The large concentration of the very small precipitates compared with the much larger but less numerous growing precipitates indicates that the very small precipitates are actually embryos which form due to compositional fluctuations. The critical size for spinel nucleation was estimated to be 4.3 nm based on the distribution in the size of very small particles. The embryos are bounded by 〈111〉 planes with an octahedral morphology which is the minimum energy morphology.

The ultra-low load indentation response of ceramic single crystal surfaces (Al2O3, SiC, Si) has been studied with a software-controlled hardness tester (Nanoindenter) operating in the load range 2–60 mN. In all cases, scanning and transmission electron microscopy have been used to characterize the deformation structures associated with these very small-scale hardness impressions. Emphasis has been placed on correlating the deformation behavior observed for particular indentations with irregularities in recorded load-displacement curves. For carefully annealed sapphire, a threshold load (for a given indenter) was observed below which the only surface response was elastic flexure and beyond which dislocation loop nucleation occurred at, or near, the theoretical shear strength to create the indentation. This onset of plasticity was seen as a sudden displacement discontinuity in the load-displacement response. At higher loads, indentations appeared to be accommodated predominantly by dislocation activity, though microcracks were observed to form ät contact loads of only tens of milliNewtons. Possibly such cracks are the incipient slip-induced nuclei for the much larger, indentation-induced cracks usually apparent only on the surface at much higher loads and often used for estimating indentation toughness. By contrast, silicon did not show this behavior but exhibited unusually large amounts of depth recovery within indentations, resulting in a characteristic reverse thrust on the indenter during unloading. TEM studies of indentations in silicon revealed less evidence of obvious dislocation activity than in sapphire (particularly at the lowest loads used) but did show residual highly imperfect–and often amorphous–structures within the indentations, consistent with a densification transformation occurring at the very high hydrostatic stresses produced under the indenter. The reverse thrust is caused by the relaxation of densified material during unloading. Thus, it appears that the low-load hardness response of silicon is controlled by a pressure-sensitive phase transformation. Though SiC has been predicted to undergo a densification transformation similar to silicon, its load-displacement behavior was found to be similar to Al2O3 suggesting that, for these contact experiments at least, the critical resolved shear stress for dislocation nucleation is exceeded before the critical hydrostatic pressure for densification is reached. In all cases, residual, plastically formed indentations were measured to be smaller than the fully loaded indentation depths would suggest, confirming that a significant portion of the deformation is elastic surface flexure. However, there is some doubt as to whether silicon displays elastic-only deformation even at very small penetration depths. The use of microstructural studies to complement nanoindentation experiments is shown to be a key route not only to interpreting the recorded load-displacement responses, but also to examining the deformation mechanisms controlling the mechanical behavior of ceramics to surface contacts at these small spatial scales.

A new NH4Bi3F10 compound was prepared, which results from a reaction between Bi2O3 and NH4F in an argon stationary atmosphere. It has a cubic fluorite-related structure isotypic with KBi3F10 with space group Fm3m (a = 11.974 Å). Further heating leads to decomposition to BiF3. IR spectra at different temperatures show the disappearance of NH4 group characteristic vibrations. Indexed x-ray diffraction pattern and IR spectra at different decomposition temperatures are given.

Thermodynamic calculations were performed for chemical vapor deposition in the Al–B–Ti–N–H–Cl–Ar system in order to determine the feasibility of multiphase deposition. Reagent species used were BCl3, AlCl3, TiCl4, NH3, H2, and Ar; B2 was substituted for BCl3 to determine changes in deposition efficiency. Temperature and input molar concentrations were varied over a range of values to establish relationships among solid deposits. Through deposition diagrams, molar efficiency plots, and partial pressure graphs, several two and three phase regions were found to exist. The calculations indicate that the following dispersed phase composites could be prepared: A1N + BN + TiN, BN + TiN, BN + TiB2, BN + TiB2 + TiN, and TiB2 + TiN.

A new family of modified ZBLAN glass compositions has been synthesized which provides better stability against crystallization. A preliminary study of the Hruby factor HR shows higher values as compared to a ZBLAN glass prepared under the same conditions, utilizing similar high purity starting materials. Large rods of clear glass with a 1.5 cm diameter and up to 17 cm in length were easily obtained. Results will be presented on the physical properties and crystallization behavior of these high stability glasses.

Unintentionally doped 3C–SiC (111) films were grown on TiC (111) substrates. The films were characterized by electrical measurements employing Pt Schottky contacts, optical microscopy, and transmission electron microscopy (TEM). The observed current-voltage (I-V) characteristics appear to be dominated by space-charge-limited-current (SCLC) conduction in the films. Analysis of the I-V characteristics has resulted in information pertaining to the electrically active defects in the films. These active defects are believed to be associated with stacking faults and point defects present in the films and contribute to traps at ∼0.656 eV below the conduction band edge. The concentration of traps was found to vary with film thickness and surface morphology.

Details of fiber pullout processes and mechanisms are addressed for a carbon fiber reinforced silicon nitride ceramic composite. The energy for fiber pullout, γpo, is experimentally measured by the work-of-fracture technique using test specimens with a circumferential notch. A precise determination of the distribution of pullout fibers combined with the experimental results of the pullout energy provides an important insight into the micromechanical processes and mechanisms of the composite fracture. Various energy dissipation processes associated with the composite fracture, the frictional interface shear stress, the Weibull modulus of the reinforcing fibers, and composite designs for improved toughening are discussed.

We previously reported bond strength measurements of metal/ceramic interfaces using shock waves to separate the bond by spallation. The technique relies on interpretation of the free surface velocity of a metal film as it is spalled from its substrate. A number of questions have been raised concerning the details of the interaction of the shock and interface. We provide answers by numerically modeling the experiments. We rederive the relationship between the maximum stress at the bond interface and the free surface velocity of the metal overlayer. We compare the analytical result with numerical calculations based on less restrictive assumptions, thereby supporting the analysis. We illustrate important design considerations of the experiment with numerical calculation and in the process, evaluate the effect of the artificial damping on the numerical results.

A study of the cross doping of GaAs layers grown by a two-step metalorganic chemical vapor deposition on Si substrates is reported. All as-grown, unintentionally doped layers of GaAs were n-type, and the carrier profiles tracked the Si atomic profiles. Furnace annealing at 850 °C for 30 min in an arsine overpressure, which is used to improve the crystalline quality of the GaAs near the heterointerface, caused additional Si to diffuse into the GaAs layer. Comparison of the Si concentration at the interface with the carrier concentration suggested the presence of compensating acceptors. Resonance Raman scattering by the SiAs local vibrational mode near the interface shows that a fraction of the Si atoms are localized at the As sites. The furnace annealing increased the Si concentration in the 1.7–1.8 μm thick initially grown GaAs layer. This, in turn, influenced the electrical profiles created with Si or Be implantation on a 2.3 μm thick GaAs layer.

TiO2 single crystal fibers in the 1 mm diameter range were pulled from different alloy melts using the laser heated pedestal melting technique. The alloying elements studied were CaO, MnO, MgO, SiO2, FeO, and Al2O3. Phase diagram solute partition coefficient, k0, maximum solid solubility limit, CS(max), eutectic concentration, CE, and eutectic temperature, TE, were determined for each of these alloys. Solute redistribution effects in the solid, controlled precipitation in the solid, smooth solid-liquid interfaces in the presence of high melt concentrations and substantial crystal broadening by fluid migration up the solid from the melt all indicated the existence of a very strong thermodynamic field and a large solid diffusion coefficient operating in the solid behind the solid/liquid interface.

Four types of structurally different, flat interfaces have been observed in ZnO-based varistor ceramics containing metal-oxides additives (Bi, Mn, and Ti) by bright-field and high-resolution imaging in a transmission electron microscope. Orientation relationships have been characterized by selected-area diffraction. The faceting of ZnO grains when in contact with β–Bi2O3 is discussed in relation to the anisotropic growth of the ZnO grains which leads to pronounced faceting parallel to (0001) planes.

Reaction kinetics between borosilicate glass (BSG) and sapphire has been studied at temperatures from 850 °C to 950 °C. Microstructural and chemical analyses show that the nonporous interdiffusion layer is formed with Al+3 ion dissolving from sapphire and K+ diffusing from BSG onto the interface of sapphire/BSG, and that both ions are always coupled together in the reaction layer. The interdiffusion layer moves toward BSG with time and the reaction starts immediately at temperatures investigated without incubation period. The growth kinetics for the interdiffusion layer follows a parabolic rate law in the temperature range investigated, and shows an apparent activation energy in the range of 176 k–/mol. The diffusion coefficient of aluminum ion is determined from EDX analysis, and the values range from 0.7–1.4 × 10−12 at 850 °C to 3.0–6.0 × 10−12 cm2/s at 950 °C. The above results also show an activation energy close to that determined from the parabolic growth rate constants, suggesting that the mass-transport kinetics of aluminum ion from sapphire into the interdiffusion layer controls the formation process.

Rising T- (or R-) curve behavior is increasingly being used in order to improve the mechanical reliability of ceramic materials. In this study, the possibility of inducing such behavior using residual compressive stresses is analyzed. The T-curves obtained for certain residual stress profiles induce crack stability when the stress minima (compressive stress maxima) lie away from the surface of the sample. The consequences of this stabilization on the strength characteristics are a significant reduction in the strength variability and strength insensitivity to the initial flaw size. In addition to these desirable features, considerable strengthening is also obtained. Hence, suitably engineered compressive stress profiles are shown to be a novel and alternative means of enhancing mechanical reliability.

The MBE growth of InxGa1−xAs (x ∼ 0.53) on silicon substrates has been investigated emphasizing the effects of substrate orientation and buffer layers between In0.53Ga0.47As and Si. It is shown that growth on silicon substrates misoriented from (001) toward a [110] direction eliminates the presence of antiphase domains. The best In0.53Ga0.47As surface morphology was obtained when a 0.9 μm epitaxial Si buffer was initially grown, followed by a pre-exposure of the silicon surface to As4 at 350 °C, followed by the growth of In0.53Ga0.47As. Threading dislocations, stacking faults, low-angle grain boundaries, and spinodal decomposition were observed by TEM in the InGaAs layers. The spinodal contrast scale was shown to depend on the buffer type and the total InGaAs thickness. Thick buffers consisted of GaAs or graded InxGa1−xAs layers, and large In0.53Ga0.47As thicknesses favor the development of a coarse-scale spinodal decomposition with periodicity around 0.1 μm. Thin GaAs buffers or direct In0.53Ga0.47As growth on Si may result in a fine-scale decomposition of periodicity ∼10 nm. The principal strain direction of the spinodal decomposition appeared along the [1$\overline 1$0] direction, parallel to the vicinal Si surface step edges. InGaAs immiscibility affects the InGaAs growth process, favoring a 3-D growth mode. X-ray diffraction measurements and photoreflectance spectra indicated that the sample quality was improved for samples exhibiting a fine-scale spinodal decomposition contrast even if they contained a higher dislocation density. Threading dislocations run almost parallel to the [001] growth axis and are not affected by strained layers and short period (InAs)3/(GaAs)3 superlattices. The lowest double crystal diffractometry FWHM for the (004) InGaAs reflection was 720 arc sec and has been obtained growing InGaAs directly on Si, while the lowest dislocation density was 3 × 109 cm−2 and was obtained using a 1.5 μm GaAs buffer before the In0.53Ga0.47As deposition.

The major problem in the NiMn2O4 system has been the determination of the valencies and the cation distribution between the two sublattices of the inverse spinel structure, in which both manganese and nickel can adopt more than one valence state. X-ray photoelectron spectroscopy (XPS) was used to elucidate the valence distribution of the manganese and nickel ions. The results showed that identification of the three Mn and two Ni species in the nickel manganite phase is possible, enabling the validity of crystal structure configurations, proposed in the literature, to be assessed. A small amount of copper, added as CuO to the system, was found to be present in both monovalent and divalent states, the Cu+ ions inducing the creation of the large amount of tetravalent Mn observed. This led to a larger number of sites for electron hopping, the mechanism of conduction, and consequently the electrical conductivity of the Cu doped material is much higher than the undoped NiMn2O4.

Nanoscale mixtures of Ge/Sn, a nominally immiscible binary system, prepared by mechanical attrition have been studied by 119Sn Mössbauer spectroscopy. The Mössbauer measurements in general reveal two sites for the Sn atoms, a tetragonal β–Sn site and another site designated as “A”. The β-Sn integrated intensity decreases in magnitude with Ge concentration, 1 – x, in Ge1−xSnx as the second A-site intensity increases. The isomer shift and the small/negligible quadrupole splitting of site A suggests it represents Sn in solid solution in the Ge lattice. This in turn represents a large (12–24 at. %) nonequilibrium solid solubility of Sn in Ge prepared by mechanical milling, compared to the equilibrium value of <1.0 at. %. Oxidation of the Sn was detected by Mössbauer spectroscopy at Sn-poor concentrations (x ⋚ 0.10) when the milling vial was not totally free of oxygen (i.e., milling in impure argon). This may be due to rapid oxidation of finely divided Sn film particles possessing a large surface-to-volume ratio at these compositions.

Some of the problems of hydrogen, nitrogen, and oxygen behavior in boron, which is a promising material for the development of sensitive elements in gas sensors of improved radiation resistance, were studied. Using gas and thermal gravimetric analysis methods the interaction of these gases with boron was investigated, and the influence of temperature and annealing on the sorptivity of boron, the interaction of disperse boron powder with the environment, and thermal gas release from boron and boron-containing materials were studied.

We have prepared a series of SnxSiO2)100−x granular metal films by RF magnetron sputtering with nominal Sn compositions from x = 30 to x = 90 at. %. X-ray diffraction and transmission electron microscopy measurements confirm that these films consist of small Sn particles, ranging from about 10 nm to 200 nm in mean diameter, embedded in an amorphous SiO2 matrix. These measurements also indicate that the mean Sn particle size decreases and the particle size distribution becomes more narrow as the Sn concentration is reduced. A differential scanning calorimeter has been used to study the size dependence of the melting temperature of the Sn particles. The melting temperature has been found to be increasingly depressed from the bulk value as the Sn particle size decreases. No evidence of an enhancement in the melting temperature at any particle size has been found. The evolution of the melting behavior of each sample with repeated melting and solidification cycles has also been studied.