In this research, a fatigue model for ferroelectric materials is proposed. The reasons for the electrical fatigue resistance of SrBi2Ta2O9 (SBT), SrBi2Nb2O9 (SBN), and PbZr1−xTixTixO3 (PZT) are discussed in terms of the bulk ionic conductivities of the compounds. To obtain the bulk ionic conductivity of SBT and SBN, we have used impedance spectroscopy which provides an effective method that allows us to separate the individual contributions of bulk, grain boundaries, and electrode-ferroelectric interfaces from the total capacitor impedance. The bulk ionic conductivities of SBT and SBN (∼10−7 S/cm) are much higher than those of the perovskite ferroelectrics, e.g., PZT (∼10−11–10−10 S/cm). The high ionic conductivities led us to conclude that the good fatigue resistance of SrBi2Ta2O9 and SrBi2Nb2O9 is due to easy recovery of defects. Specifically, oxygen vacancies entrapped within the capacitors are easily released, resulting in limited space charge buildup and domain wall pinning during the polarization reversal process. However, the oxygen vacancies in PZT are trapped at trap sites to become space charges, resulting in capacitor fatigue.

The Weibull modulus is widely used for estimating the reliability of ceramic components in engineering applications. An improvement in the evaluation of the Weibull modulus is achieved by using an appropriate weight function to the data points while fitting a straight line to the Weibull plot by the least square method. The conventional weight function is a function of the probability of failure. This paper describes an alternate method of obtaining the weight function based on first principles. This modified weight function is a function of the stress at failure rather than probability of failure. Evaluation of the two-parameter Weibull modulus was estimated on simulated strength distribution data with both the weight functions. A comparative analysis indicates that the modified weight function gives a different result than the conventional weight function. The paper also highlights the effect and importance of uncertainties in the measurement of strength on the calculated Weibull modulus.

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.

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.

Decomposition behavior of Ln2Mn4/3W2/3O7 (Ln = Eu and Er) in reducing atmosphere at 1273 K was determined. These compounds decomposed to LnMnO3 and Ln2MnWO7 at PO2 = 10−8.46 atm for Ln = Eu and 10−7.46 atmosphere for Ln = Er, respectively. Decomposition product Eu2MnWO7 decomposed to Eu2MnWO6 at PO2 = 10−15.67 atm, while Er2MnWO7 decomposed to Er2O3, MnO, and W less than 10−17 atm. The standard Gibbs free energy changes of decomposition for Eu2Mn4/3W2/3O7, Eu2MnWO7, and Er2Mn4/3W2/3O7 at 1273 K were determined to be 34.4 kJ · mol−1, 191.9 kJ · mol−1, and 44.8 kJ · mol−1, respectively. The standard Gibbs free energy changes of formation of Er2Mn4/3W2/3O7 and Er2MnWO7 were also determined to be −2429.5 and −2463.2 kJ · mol−1 at 1273 K, respectively.

TiB2, along with MgO and Mg3B2O6, was formed by a thermite reaction between Mg, amorphous B2O3, and TiO2 powders in argon. The mixture 5Mg–TiO2–B2O3 along with binary mixtures and single components were analyzed using differential thermal analysis (DTA) and x-ray diffraction (XRD). Large (25 g) specimens were also ignited in bulk using a resistance-heated nichrome wire. The reaction path in forming TiB2 in the three component mixture was deduced. Mg reduces TiO2 and B2O3 to form Ti and MgB2, respectively, which in turn react to form TiB2. In an oxidizing atmosphere, the significant speed of the reaction permitted solid state reaction to form TiB2 before atmospheric oxygen could diffuse into the powder mass and react to form oxide phases. Thermite reactions in air have the advantage (over furnace heating in air) of not providing time at elevated temperatures for Mg and intermediate products to become consumed in the formation of oxides, nor time for oxidation degradation of TiB2.

Synthesis and the thermal decomposition behavior of new molecular precursors, strontium, and calcium zirconyl citrates are presented. The pathway to the metazirconate formation has been found to proceed through a multistep process. The precursors yield SrZrO3 and CaZrO3 fine powders at temperatures as low as 650 °C. Physico-chemical, spectroscopic, thermoanalytical, and microscopic techniques have enabled the identification of the sequence of events leading to the perovskite formation and proposition of a thermolysis scheme. Retention of the molecular level mixing of the metal ions during the course of the precursor decomposition is supported by these techniques. Prior to the formation of MZrO3 (M = Sr and Ca) an ionic oxycarbonate, M2Zr2O5CO3 (M = Sr and Ca), intermediate is produced by the thermal decomposition of the citrate precursors.

We have investigated mechanical probing of a precracked fine line structure as a new type of thin film fracture mechanics specimen. An idealized mechanics analysis is first presented. Experimentally, two types of precracks are formed. A thin carbon layer to which other layers weakly adhere creates a “processed precrack” by integrated circuit processing techniques. An “indented processed precrack” is formed by precision alignment of a sharp microwedge. The processed precrack is found to reduce the critical tangential load by 50% from a non-precracked line, while the indented processed precrack lowers the load by 200%. From this, a reasonable value of adhesion may be directly calculated. Crack path behavior is observed to depend on strength of the interface. In the case of a weak interface, the crack remains in the interface as it extends. For a strong interface, it kinks into the substrate if the crack is initially short, but remains in the interface if it is initially long. Given the experimental evidence, the mechanics are slightly modified to quantitatively model the experimental data.

A sequential analysis of the growth of diamond films on silicon substrates in a microwave plasma assisted chemical vapor deposition (CVD) reactor has been performed by Raman spectroscopy. The plasma was switched off during measurements, but the substrate heating was maintained to minimize thermoelastic stresses. The detectivity of the present experimental setup has been estimated to be about a few tens of μmg/cm2. From such a technique, one expects to analyze different aspects of diamond growth on a non-diamond substrate. The evolution of the signals arising from the substrate shows that the scratching treatment used to increase the nucleation density induces an amorphization of the silicon surface. This surface is annealed during the first step of deposition. The evolution of the line shape of the spectra indicates that the non-diamond phases are mainly located in the grain boundaries. The variation of the integrated intensity of the Raman signals has been interpreted using a simple absorption model. A special emphasis was given to the evolution of internal stresses during deposition. It was verified that compressive stresses were generated when coalescence of crystals took place.

The laser ablation of stationary KNbO3 single crystal targets induces a Nb enrichment of the target surface. In rotated targets this effect is observed only in those areas irradiated with low laser fluence. The composition of the plasma formed close to the target surface is congruent with the target composition; however, at further distances K-deficient films are formed due to the preferential backscattering of K in the plasma. This loss may be compensated for by using K-rich ceramic targets. Best results so far have been obtained with [K]/[Nb] = 2.85 target composition, and crystalline KNbO3 films are formed when heating the substrates to 650 °C. Films formed on (100)MgO single crystals are usually single phase and oriented with the (110) film plane parallel to the (100) substrate surface. (100)NbO may coexist with KNbO3 on (100)MgO. At substrate temperatures higher than 650 °C, niobium diffuses into MgO forming Mg4Nb2O9 and NbO, leading to K evaporation from the film. Films formed on (001) α–Al2O3 (sapphire) show the coexistence of (111), (110), and (001) orientations of KNbO3, and the presence of NbO2 is also observed. KNbO3 films deposited on (001)LiNbO3 crystallize with the (111) plane of the film parallel to the substrate surface. For the latter two substrates the Nb diffusion into the substrate is lower than in MgO and consequently the K concentration retained in the film is comparatively larger.

In this study, amorphous carbon coatings were deposited with thicknesses ranging from 20 nm to 100 nm on single-crystal silicon substrates by sputtering, ion beam, and cathodic arc deposition techniques. An indentation system with a three-plate transducer with electrostatic actuation and capacitive sensor has been used to make load displacement measurements and subsequently carry out in situ imaging of the indents. Indentation experiments were carried out using a three-sided pyramidal (Berkovich) diamond tip. Measurements include load-displacement curves and calculation of hardness and Young's modulus of elasticity at various indentation depths, studies of hysteresis behavior, creep behavior, and strain rate effect of various carbon coatings. The cathodic arc coating exhibited the highest hardness and elastic modulus followed by the sputtered and ion beam coatings.

The magnetic properties and crystallographic alignment for Fe–Nd–B–Al magnets having different Nd contents were studied. It was found that higher Nd concentration (above 18 at. %) resulted in deterioration of the alignment. Also, extended ball milling of the powder particles resulted in poorer alignment of the grains in the final sintered magnet. This behavior was attributed to the cold welding of the small particles of the Fe14Nd2B phase by a mechanically soft Nd-rich phase in the course of ball milling.

Copper particles of sizes in the range 3.1 to 11.4 nm have been grown within gel compositions of the system CuO–SiO2 by an electrodeposition process applying voltages varying from 5 to 15 V. Composite films of these metal particles dispersed in a polystyrene matrix have been prepared on Corning No. 7059 glass slides by a dip-coating technique and their optical absorption characteristics have been delineated. The spectra show maxima at wavelengths in the range 380 to 470 nm, depending on the particle size. The results have been analyzed using the Mie theory. The electrical conductivity as extracted from this analysis is found to have reasonable correspondence with data reported earlier for copper nanoparticles in glass-ceramic systems.

The shear-lag type model due to Cox (Br. J. Appl. Phys. 3, 72 (1952) is widely used to calculate the deformation properties of fibrous materials such as short fiber composites and random fiber networks. We compare the shear-lag stress transfer mechanism with numerical simulations at small, linearly elastic strains and conclude that the model does not apply to random fiber networks. Most of the axial stress is transferred directly from fiber to fiber rather than through intermediate shear-loaded segments as assumed in the Cox model. The implications for the elastic modulus and strength of random fiber networks are discussed.

A combination of experiments and detailed kinetic modeling was used to investigate diamond deposition chemistry in low pressure combustion synthesis. Microprobe sampling was employed to provide in situ, quantitative measurements of the stable gas-phase species impinging the growth surface. The reactant gas ratio was found to be the most critical experimental variable. A detailed kinetic model was developed for the stagnation flow system. Comparison of experimental measurements showed very good agreement with model predictions. The model was then used to predict the concentration of radical species and analyze the sensitivity of predictions to γH, the probability of atomic hydrogen recombination on the surface. It was shown that γH dramatically affects the distribution of radical species near the diamond surface. The analysis also indicates that atomic carbon may be an important gas-phase precursor in this system. Comparison of mole fraction measurements and observations of film morphology were used to draw conclusions on the growth mechanism.

Camber (curvature) development during cofiring a two-layered structure of Ag film/low-dielectric-constant, low-temperature cofired ceramic (LTCC) green tape has been investigated. At a given thickness of Ag film, both the camber and camber rate decrease linearly with increasing the square thickness of LTCC. Densification mismatch between Ag and LTCC is attributed to be the root cause for the camber generation during cofiring. Mathematical analysis is made to theoretically describe the camber development, and the results show a fairly good agreement with experimental observations.

An infrared study is made of the chemical changes of synthetic schwertmannite, which normally is a coal oxidation by-product formed by thiobacillus ferrooxidan bacteria. Schwertmannite, a class of minerals, is a metastable compound that transforms to jarosite, hematite, and/or basic iron sulfate at relatively low temperatures, and is analogous in structure to basic iron sulfate, but with a –Fe–O– cage. A proposed formula for schwertmannite is Fe4O4(OH)2·AN(2/e) * nH2O, where AN is the anion and e is its charge, where sulfate can be replaced with other anions, a possible catalyst. The facile conversion of schwertmannite to a black or yellow material might make a useful raw material for the pigment industry.

In the context of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, thin (60 ± 10 nm) photocatalytic films of TiO2 were formed by a sol-gel process on (a) soda lime glass, (b) the proton-exchanged surface of soda lime glass, and (c) fused silica. The hypothesis that diffusion of sodium oxide from the soda lime glass into the titanium dioxide layer during the calcination step causes the lower photoefficiency in films on glass was tested and proven. At high concentration sodium prevented formation of the photoactive anatase phase and, at low concentration, introduced surface and bulk recombination centers. Sodium transport was efficiently blocked by a thin layer at the interface of proton-exchanged (“hydrogen”) glass and nascent TiO2, formed at 400 °C of a poly(titanyl acetylacetonate) TiO2 precursor. The sodium transport blocking layer did not form and the highly photocatalytic film was not obtained when the TiO2-precursor film was applied to glass that was not proton exchanged. Furthermore, only a much less effective sodium transport blocking layer was formed on glass that was proton-exchanged, but was calcined at 400 °C prior to application of the TiO2 precursor layer, showing that the sodium depleted glass surface, by itself, was a less effective barrier against sodium transport than the interfacial product of hydrogen glass and the TiO2 precursor.

Metal-silica nanocomposites with different metal volume fractions have been prepared via solid state exchange reactions induced by ball milling followed by a reduction treatment in H2 flux. In nickel-containing mixtures oxygen transfers directly from NiO to Si while NiO is reduced to Ni. When NiO is present in a large ratio, its excess can be reduced by a thermal treatment in H2 flux. Nickel crystallites are obtained with nanometer size in the milling process and there is no significant growth during thermal treatment. Similar process conditions applied to Fe-containing mixtures give rise to a more complex reaction path which prevents the complete conversion of Fe(III) to Fe. Nickel-silica and iron-silica nanocomposites are also produced by ball milling mixtures of either nickel or iron with amorphous silica.

Ultra low-load-dynamic microhardness testing facilitates the hardness measurements in a very low volume of the material and thus is suited for characterization of the interfaces in MMC's. This paper details the studies on age-hardening behavior of the interfaces in Al–Cu–5SiCp composites characterized using this technique. Results of hardness studies have been further substantiated by TEM observations. In the solution-treated condition, hardness is maximum at the particle/matrix interface and decreases with increasing distance from the interface. This could be attributed to the presence of maximum dislocation density at the interface which decreases with increasing distance from the interface. In the case of composites subjected to high temperature aging, hardening at the interface is found to be faster than the bulk matrix and the aging kinetics becomes progressively slower with increasing distance from the interface. This is attributed to the dislocation density gradient at the interface, leading to enhanced nucleation and growth of precipitates at the interface compared to the bulk matrix. TEM observations reveal that the sizes of the precipitates decrease with increasing distance from the interface and thus confirms the retardation in aging kinetics with increasing distance from the interface.