bluuebunny/crossref_metadata_2025 huggingface dataset:
Appraisal of Current Homogenizing Techniques for the Elastic Response of Porous and Reinforced Glass
Authors: Ferrari Mauro , Filipponi Marco
Published: March 2005

Some classical and recent homogenizing theories are discussed. The predicted effective moduli are compared with experimental results, for porous glass, and for glass containing alumina or tungsten reinforcements. Particular attention is given to the Mori–Tanaka approach, in view of its application to problems of current technological significance.
Effect of Temperature on the Ultimate Strength and Modulus of Whisker‐Reinforced Ceramics
Authors: Carroll Douglas R. , Dharani L. R.
Published: March 2005

Whiskers are a very attractive means of reinforcing a ceramic material. It has been shown that the whiskers dramatically improve the ultimate strength and modulus of the materials at room temperature. However, recent studies indicate that at high temperatures the improvement is less pronounced, or there is no improvement at all. In this paper a model is developed to explain why the properties are degraded at high temperature. The parameters which seem most important for high‐temerature performance are the coefficients of thermal expansion and Poisson's ratios for the constituents, the heat treatment temperature, and the cofficeint of friction between the whisker and the matrix. The model compares favorably with the experimental data available, so a parametric study was done to show the effect of different parameters on the strength and modulus of the composite.
Elastic Properties of Al2O3 and Si3N4 Matrix Composites with SiC Whisker Reinforcement
Authors: Fisher Edward S. , Manghnani Murli H. , Wang Ji‐Fan , Routbort Jules L.
Published: March 2005

A study of the elastic moduli of Al2O3 and Si3N4 ceramics reinforced with 0 to 25 wt% SiC whiskers has been performed. The Young's moduli, shear moduli, and longitudinal modulus are compared with calculated predictions for aligned fiber composites by Hill and Hashin and Rosen, and for fibers randomly oriented in three dimensions by Christensen and Waal. The measured values are in excellent quantitative agreement with those derived for the random orientation of the SiC whiskers.
Crystal Structures of Ca5Cr3O12 and Ca5Cr2SiO12, the Chromium Analogs of Silicocarnotite
Authors: Adendorff Keith T. , de Villiers Johan P. R. , Kruger Gert J.
Published: March 2005

The crystal structures of Ca5Cr3O12 and Ca5Cr1.8Si1.2O12, the chromium analogues of silicocarnotite, Ca5P2SiO12, have been determined. Both compounds were grown at 1250°C and analyzed by electron microprobe analysis. Diffraction data collection was done on spherically ground crystals which are both orthorhombic with space group Pnma. Charge‐balance requirements as well as siteoccupancy refinement of the Si‐containing compound point strongly to the presence of both tetravalent and hexavalent chromium in tetrahedral sites. The Si is located together with tetravalent Cr in a general position, whereas the hexavalent Cr is situated on a mirror plane. The calcium atoms are located in seven‐, eight‐, and nine‐coordinated sites. The presence of vacant channels of 3.5 Å diameter perpendicular to (100) is a feature of this structural type. Its relation to the apatite and glaserite structures is also shown.
Phase Identification and Electrical Properties in ZnO–Glass Varistors
Authors: Lee Yih‐Shing , Tseng Tseung‐Yuen
Published: March 2005

Ceramic varistors based on ZnO with lead zinc borosilicate glass instead of Bi2O3 were prepared. The effect of sintering conditions on the electrical properties was studied by sintering samples at various temperatures and cooling them at different rates. The sample sintered at 1250°C for 1 h, then furnace cooled, possessed the best electrical properties, as characterized by the highest nonlinear coefficient, lowest leakage current, and lowest degradation. The microstructure and crystal structure of the glass phase of ZnO–glass varistors were examined by means of scanning electron microscopy, transmission electron microscopy, and powder X‐ray diffractometry. The glass phase was originally amorphous, but crystallized as an intergranular layer in the sintered and furnace‐cooled samples. This crystallized phase was a zinc borate phase (5ZnO·2B2O3), which was identified by X‐ray diffractometry, transmission electron microscopy, and Auger electron spectroscopy. The zinc borate phase at the grain boundary of ZnO–glass samples enhanced the nonohmic characteristics of the ceramic varistors.
Oxidation Resistance of Alumina–Titanium Nitride and Alumina–Titanium Carbide Composites
Authors: Tampieri Anna , Bellosi Alida
Published: March 2005

The presence of TiC or TiN paritcles in an Al2O3 matrix affects the thermal stability of the composites in oxidizing environments. In isothermic oxidation tests at 700°, 800°, 900°, 1000°, and 1100°C for up to 20 h, two different oxidation regimes have been observed at T < 900°C and at 900°C ≤T≤ 1100°C. At low temperatures (T < 900°C), the oxidation follows a phase‐boundary reaction; the reaction product initially consists of aggregates of submicrometer needlelike TiO2 rutile crystals that subsequently grow and coalesce. When a continuous TiO2 rutile layer is formed (T≥ 900°C), the oxidation kinetics change to parabolic, and the diffusion of O2 through a thick TiO2 layer is proposed as the governing step.
Aging of the Weak‐Field Dielectric Response in Fine‐ and Coarse‐Grain Ceramic BaTiO3
Authors: Wu Kaiwen , Schulze Walter A.
Published: March 2005

BaTiO3 ceramics with grain sizes of 0.6 to 6 mm and relative densities of 89% to 92% were prepared by hot forging and conventional sintering from high‐purity oxalate‐derived powder. The aging of both the dielectric constant and the dielectric loss was examined with respect to grain size, temperature, and frequency. It is suggested that the main aging mechanism in coarse‐grained BaTiO3 is the aging of hysteretic domain wall motion. The dielectric aging is a thermally activated process and shows two aging rates when observed at a temperature of 8°C for coarse‐grained ceramics.
Properties and Network Constitution of rf‐Sputtered Amorphous Films in the System Silicon Dioxide–Aluminum Orthophosphate
Authors: Hanada Teiichi , Ando Akihiro , Tanabe Setsuhisa , Soga Naohiro
Published: March 2005

Amorphous films in the system SiO2–AlPO4 were prepared by means of the rf‐sputtering method, and their physical properties, such as density, refractive index, and temperature coefficient of Young's modulus, and infrared spectra were measured. Also, the Kα X‐ray emission spectra of silicon and aluminum were measured in order to investigate the coordination state of these cations in the amorphous films. The density and the refractive index were close to those of amorphous SiO2 and AlPO4 and the compositional dependence showed a small deviation from linearity. The temperature coefficients of Young's modulus were positive for all of the samples. The infrared absorption spectra of all of the samples were similar to those of SiO2 glass and amorphous AlPO4 film, and there was no evidence of the presence of P═O bonds. The coordination states of silicon and aluminum ions in the present amorphous films were the same as those in fused silica and AlPO4 crystal, respectively. The results of the properties, infrared absorption spectra, and X‐ray emission spectra suggest that SiO4 tetrahedrons and AlO4–PO4 connecting tetrahedral dimers constitute the network of the present amorphous films. A small deviation of the physical properties from an additive rule was thought to result from the difference in the bond character between the newly formed Si–O–Al and Si–O–P bonds and the bonds in the end members, Si–O–Si and Al–O–P.
Summary of Stress‐Dependent Activation Energy for Lightguide Fibers
Authors: Inniss Daryl , Kurkjian Charles R. , Brownlow Darryl L.
Published: March 2005

Recent reports have suggested that an exponential dependence of failure time on applied stress provides a more fundamental description of fatigue, but the power law is usually used to assess the long‐term mechanical reliability of lightguide fibers. A consequence of the exponential expression is a linear dependence of applied stress and activation energy. This study applies the exponential law to all temperature‐dependent fatigue data for lightguide fibers reported in the literature. The results show consistency with the prediction of the exponential expression.
Snubbing and Bundling Effects on Multiple Crack Spacing of Discontinuous Random Fiber‐Reinforced Brittle Matrix Composites
Authors: Wu Hwai‐Chung , Li Victor C.
Published: March 2005

Multiple cracking due to pseudo strain–hardening of fiber‐reinforced brittle matrix composites contributes significantly to enhanced composite strain capacity as well as toughness. This unique phenomenon is true for both continuous aligned and discontinuous random fiber composites. Theoretical formulation of multiple crack spacing is reviewed in this paper. In particular, a snubbing effect of fiber pullout and a bundling effect of fiber strands on crack spacing are discussed. Taking account of these effects, expressed via the snubbing coefficient, f, and effective bond strength, τeff, a better spacing prediction has been obtained for a discontinuous random glass‐strand‐reinforced cement composite.
Oxidation Behavior of Rare‐Earth Disilicate–Silicon Nitride Ceramics
Authors: Cinibulk Michael K. , Thomas Gareth , Johnson Sylvia M.
Published: March 2005

The oxidation behavior and microstructure of the oxidized surfaces of RE2Si2O7–Si3N4 ceramics were investigated. The high oxidation resistance of these materials at 1400°C is attributed to the minimization of amorphous phases via devitrification to disilicates that are in equilibrium with SiO2, the oxidation product of Si3N4. Crystals of RE2Si2O7 grew out of the surface silicate in prefered orientations that were dictated by crystal structure. The morphology of the microstructure of the oxidized surfaces was shown to be partially dependent on the concentration of impurities; the presence of Ca was found to coincide with the growth of Gd2Si2O7 and Dy2Si2O7 crystals with high aspect ratios.
Pyroelectric and Electrostrictive Properties of (1 –x–y) PZN ·xBT ·yPT Ceramic Solid Solutions
Authors: Kumar Umesh , Cross L. Eric , Halliyal Arvind
Published: March 2005

The pyroelectric and electrostrictive properties of lead zinc niobate–lead titanate–barium titanate (PZN–BT–PT) ceramic solid solution were investigated. These properties of the (1 –x)PZN ·xBT series were qualitatively explained with a composition fluctuation model. The pyroelectric depolarization temperatures of (1 –x–y)PZN ·xBT ·yPT ceramics were utilized to select compositions for room‐temperature electrostrictive applications. Among them, 0.85PZN · 0.10BT · 0.05PT ceramic with Q11= 0.018 m4/ C2, Q12=−0.0085 m4/C2, s2 at 25 kV/cm =−6.1 × 10−4, Tmax= 75°C at 1kHz, and Tt= 27°C shows optimum properties for micropositioner applications.
Stabilization and Characterization of Nanosized Niobium and Tantalum Oxide Sols — Optical Applications for High‐Power Lasers
Authors: Parraud Stephen , Hubert‐Pfalzgraf Liliane G. , Floch Hervé G.
Published: March 2005

Stable nanosized particles of niobium and tantalum oxides were obtained by hydrolysis of the metal ethoxides in ethanol with triethylamine. These sols were amorphous hydrated oxides M2O5·nH2O. They were used to prepare thin porous films on SiO2 disks via spin‐coating techniques. These coatings displayed thicknesses ranging from 100 to 300 nm and a refractive index of about 1.7. Laser damage tests at 1053‐nm wavelength with a pulse duration of 3 ns were conducted on the single‐layer systems. Ta2O5 coatings exhibited much higher threshold values (averaging 14.5 ± 2.1 J/cm2) than those of Nb2O5 (averaging 8.3 ± 1.6 J/cm2). Buildup of multilayer stacks of high‐ and low‐index materials was prevented because of internal stress.
Electrical Properties of Cubic, Stabilized, Single ZrO2–Gd2O3 Crystals
Authors: Kang Thae‐Khapp , Nagasaki Takanori , Igawa Naoki , Il‐Hiun Kuk , Ohno Hideo
Published: March 2005

Electrical properties of single‐crystal, cubic ZrO2 solid solutions containing 10.0, 12.5, and 15.0 mol% Gd2O3 were investigated. Electrical conductivities were measured by a two‐terminal ac technique up to 831°C in air, and the observed data were compared with those reported for polycrystalline materials. Electrical conductivity and activation energy increased, and preexponential factor decreased with Gd2O3 content.
Influence of Oxygen on the Formation of Aluminum Silicon Carbide
Authors: Oscroft Robert J. , Thompson Derek P.
Published: March 2005

X‐ray diffraction studies have been used to follow the formation of Al4SiC4 from Al4C3 and SiC and the role played by impurity oxygen. The phase Al2OC forms in the early stages of reaction and reacts with SiC at ≈ 1700°C to produce Al4SiC4 plus a small amount of an aluminosilicate liquid. This liquid dissociates at higher temperatures, the resulting evolution of gases hindering complete densification. Higher densities are obtained on hot‐pressing.
Oxidation Kinetics of Hafnium Carbide in the Temperature Range of 480° to 600°C
Authors: Shimada Shiro , Inagaki Michio , Matsui Kunihito
Published: March 2005

The isothermal oxidation of HfC powders was carried out at temperatures of 480° to 600°C at oxygen pressure of 4, 8, and 16 kPa, using an electromicrobalance. The oxidized product was identified by X‐ray analysis, Raman spectroscopy, X‐ray photoelectron spectroscopy, and electron diffraction, and the morphology of the oxidized grains was observed by scanning electron microscopy. Oxidation proceeds by two processes: a diffusion‐controlled process operates up to about 50% oxidation and a phase‐boundary‐controlled process operates above about 50% oxidation. The activation energies for both processes are the same (197 ± 15 kJ.mol−1). The change in the oxidation process is associated with the generation of cracks on the grains, resulting from the growth or expansion stress due to the formation of monoclinic HfO2 microcrystallites less than 3 nm in size. In the latter process, the thickness of the diffusion layer is kept constant, being time‐independent, which allows the process to apparently obey the phase‐boundary‐controlled reaction.
Dynamic Fracture Characterization of Al2O3 and SiCw/Al2O3
Authors: Deobald Lyle R. , Kobayashi Albert S.
Published: March 2005

The dynamic stress intensity factors, which were determined with newly developed bar impact facilities and a new data reduction procedure, for an Al2O3 ceramic and 29 vol% SiCw/Al2O3 composite were virtually identical, thus indicating that the short SiC whiskers were ineffective under dynamic fracture. SEM studies revealed five distinct fracture morphologies with increased percentage area of transgranular fracture in both materials with rapid crack propagation. Also, the high dynamic stress intensity factor caused multiple microscopic crack planes to form and then join as the crack advanced.
Thermal Conductivity of Boron Carbide–Boron Nitride Composites
Authors: Ruh Robert , Donaldson Kimberly Y. , Hasselman D. P. H.
Published: March 2005

Because of their preferred orientation, the addition of boron nitride dispersions to hot‐pressed boron carbide was found to result in a considerable degree of anisotropy in thermal conductivity of the resulting composite, indicated by an increase in the thermal conductivity perpendicular to the hot‐pressing direction by as much as a factor of 3 at the highest boron nitride volume fractions of this study, and a decrease in the thermal conductivity parallel to the hot‐pressing direction by as much as a factor of 2. The composite data were found to be below the values expected from composite theory, which may represent indirect evidence for the existence of an interfacial thermal barrier.
Composition and Appearance of Magnesium Silicate Hydrate and Its Relation to Deterioration of Cement‐Based Materials
Authors: Bonen David
Published: March 2005

Magnesium sulfate's attack on cement‐based materials results in massive deposition of gypsum and brucite accompanied by decalcification of calcium silicate hydrate (CSH) (the binding material of the cement). Magnesium silicate hydrate (MSH) appears as a late‐stage product, mainly on deteriorated surfaces, and replaces the decalcified CSH. MSH appears as an inhomogeneous phase forming an intimate mixture with brucite. The Mg:Si ratio of the MSH is lower than the equivalent Ca:Si ratio of the CSH and is probably close to 1. The deterioration itself is primarily attributed to the decalcification of the CSH rather than its replacement by MSH.
Hydrothermal Synthesis of Acicular Lead Titanate Fine Powders
Authors: Cheng Humin , Ma Jiming , Zhao Zhenguo , Qiang Di , Li Yongxiang , Yao Xi
Published: March 2005

A pure, acicular lead titanate (PbTiO3) fine powder with a white color has been prepared by hydrothermal synthesis. It is a new phase of PbTiO3 with I4 symmetry, cell parameters of a= 12.358 Å and b= 14.541 Å, and a density of 6.80 g.cm−3. The influences of pH (12.5 to 14.4), Pb/Ti ratio (1.0 to 1.6) in the feedstock, reaction temperature (130° to 230°C), time (0.25 to 4 h), starting materials, and additives on the formation of acicular PbTiO3 under hydrothermal conditions have been investigated. The acicular PbTiO3 with I4 symmetry, referred to as the PX phase, can be converted to the perovskite‐type (PE phase) of PbTiO3 at about 605°C while its acicular morphology is essentially unchanged. The preferable conditions for preparing pure acicular PX‐phase PbTiO3 are that the pH is 13.0 to 14.0, Pb/Ti ratio is >1.3, reaction temperature is 170° to 200°C, time is 0.5 to 1.0 h, titanium butoxide (Ti[O(CH2)3CH3]4) is the starting material, and poly(vinyl alcohol) is an additive. The acicular grain of the PX phase is usually less than 100 nm in diameter and more than 1000 nm in length.
Structure of Sodium Aluminosilicate Glass Surfaces
Authors: Zirl David M. , Garofalini Stephen H.
Published: March 2005

Sodium aluminosilicate (NAS) glass surfaces with compositions containing approximately 63% SiO2 and Al/Na ratios, R, of 0.25 R 2.0 were simulated using the molecular dynamics technique with a multibody interaction potential. There were changes to the surface structure and composition in comparison to bulk NAS glasses. The changes included an increased concentration of sodium and oxygen and the formation of nonbridging oxygen at the outermost surfaces, although the increases were smaller with increased Al concentration. In addition, the formation of small‐membered rings and three‐coordinated aluminum occurred in the subsurface regions. These changes were accompanied by a change in the ratio of Al/Na in the region extending to 4 Å below the surface.
Prediction and Explanation of Aging Shrinkage in Tape‐Cast Ceramic Green Sheets
Authors: Nahass Paul , Pober Richard L. , Rhine Wendell E. , Robbins William L. , Bowen H. Kent
Published: March 2005

A simple test to predict linear shrinkage of tape‐cast green sheets as a function of time was developed. Shrinkage was found to correlate inversely with the amount of organic phase bound to ceramic particle surfaces. The test was developed for alumina green tapes with acrylic binder. The correlation was found to be independent of the medium used for the two slurry systems evaluated, water and toluene/ethanol. Treatments developed to dimensionally stabilize green sheets reduced shrinkage after 35 days of aging to less than 0.15%. Stabilization treatments involved heating and/or polymer swelling which facilitated the binding of organic phase to alumina particles, causing the tape to be in a more relaxed state.
Effect of H2O and CO2 on Dielectric Properties of Single‐Crystal Cordierite and Comparison with Polycrystalline Cordierite
Authors: Shannon Robert D. , Mariano Anthony N. , Rossman George R.
Published: March 2005

The dielectric constants and dielectric loss values of two naturally occurring cordierite single crystals were determined at 1 MHz using a two‐terminal method and empirically determined edge corrections. The results are as follows. Cordierite 1: κ′a= 5.653, tan δ= 0.009; κ′b= 6.106, tan δ= 0.003; κ′c= 5.658, tan δ= 0.010. Cordierite 2: κ′a= 5.765, tan δ= 0.0006; κ′b= 6.334, tan δ= 0.0007; κ′c= 5.807, tan δ= 0.0007. The agreement between measured dielectric polarizabilities as determined from the Clausius–Mosotti equation and those calculated from the sum of oxide polarizabilities according to αD (mineral) =ΣαD (oxides) neglecting the channel H2O and CO2 for these two cordierite samples is ∼20%. Inclusion of the effects of water and CO2 assuming mobile H2O molecules with no correlation between their dipoles improves the agreement to ∼2%. Comparison of dielectric constants of manufactured cordierite ceramics shows a discrepancy between typical observed values of 4.5–5.0 and a theoretical value of 4.0 calculated from the Clausius–Mosotti equation. In certain cases, this discrepancy can be accounted for by the presence of high‐κ′ impurities, but in others there is no explanation for the differences.
Morphology of Zirconia Synthesized Hydrothermally from Zirconium Oxychloride
Authors: Mottet Bruno , Pichavant Michel , Bény Jean‐Michel , Alary Jean‐André
Published: March 2005

Monoclinic zirconia has been synthesized hydrothermally from zirconium oxychloride in the range 20–100 MPa, 250–650°C, for run duration from 20 to 100 h and in the presence of NaOH, Na2CO3, Na2SO4, NH4F, HNO3, and H2SO4 additives. Isometric, platelike, and elongated crystal morphologies were obtained depending on the additive. Both spherulitic and isolated textures were encountered with H2SO4. Growth of isometric crystals follows a general dissolution–precipitation mechanism. For H2SO4, two growth steps were identified: an early spherulitic step followed by an isolated crystals step resulting from Ostwald ripening of preexisting spherulites. The formation of spherulites is consistent with the specific properties of the sulfuric hydrothermal medium.
Microscopic Calculation of Dielectric Loss at Microwave Frequencies for Complex Perovskite Ba(Zn1/3Ta2/3)O3
Authors: Sagala Djuniadi A. , Nambu Shinji
Published: March 2005

The dielectric loss tangent at microwave frequencies for the complex perovskite Ba(Zn1/3Ta2/3)O3 was calculated with respect to the degree of structural disorder on B sites. Starting out from the equations of ion motion, dielectric loss was expressed in terms of the pair‐correlation functions corresponding to the ordering of Zn and Ta ions on B sites. The characteristic length included in the pair‐correlation functions corresponds to the average size of the region containing disorder in ion arrangements on B sites; thus the relation between the structural disorder on the B site and the dielectric loss tangent at microwave frequencies was clarified theoretically. The numerical results show that the microwave loss tangent values change their power from – 3 to – 6 with increasing degree of order on the B site, which agrees well with the experimental observations. Results obtained here confirm the physical origin of the microwave loss of complex perovskite Ba(Zn1/3Ta2/3)O3.
Thermal Transformation of X‐Alumina Formed by Thermal Decomposition of Aluminum Alkoxide in Organic Media
Authors: Inoue Masashi , Kominami Hiroshi , Inui Tomoyuki
Published: March 2005

Thermal decomposition of aluminum sec‐alkoxide in inert organic solvents at 300°C yielded a product composed of agglomerates of 4‐ to 20‐nm particles having the χ‐alumina structure. The χ‐alumina was stable and maintained a surface area above 100 m2/g until its transformation at 1150°C to α‐alumina.
Preparation and Characterization of Aluminum Borate
Authors: Ray Siba P.
Published: March 2005

Aluminum borate, 9Al2O3·2B2O3 or Al18B4O33, was synthesized by the reaction of stoichiometric amounts of α‐Al2O3 and B2O3. The Al18B4O33 material was formed into a dense ceramic by pressureless sintering with CaO, MgO, or CaAl2B2O7 additives. The material was characterized by low bulk density, moderate coefficient of thermal expansion (3 × 10−6/°C to 5 × 10−6/°C), moderate strength (210 to 324 MPa), and low dielectric constant.
Positive‐Temperature‐Coefficient Effect in Graphite–Cristobalite Composites
Authors: Ota Toshitaka , Yamai Iwao , Takahashi Junichi
Published: March 2005

An anomalous positive temperature coefficient (PTC) of resistance was found in a conductor–insulator ceramic composite. The composite materials was composed of randomly dispersed conducting graphite and insulating cristobalite‐form SiO2 particles. The PTC effect occurred at exactly 230°C, that is, at a reversible phase inversion point with a large thermal expansion of cristobalite. The magnitude of the PTC anomaly was high in composites located in the middle of the percolation curve, and loaded with large graphite and fine SiO2 particles.
Bioactivity of Zirconia‐Toughened Glass‐Ceramics
Authors: Kasuga Toshihiro , Yoshida Masahiro , Ikushima Akira J. , Tuchiya Maki , Kusakari Haruka
Published: March 2005

Bioactivity of zirconia‐toughened glass‐ceramic composites was evaluated by their surface reaction in simulated body fluid and the bonding strength to living bone. The composite containing 30 vol% zirconia showed high bioactivity, whereas that containing 50 vol% zirconia, extremely low. TEM observation indicated that Ca in the glass‐ceramic particles reacted with the zirconia during sintering. It was found that the decrease in Ca in the particles degraded the bioactivity of the composite. In this study, the optimum composition was determined for high‐strength and bioactive ceramic.
Computer Simulation of Kinetics of Spinodal Decomposition in the Tetragonal TiO2–SnO2 System
Authors: Nambu Shinji , Sato Akinori , Sagala Djuniadi A.
Published: March 2005

Computer simulation was carried out for the kinetics of spinodal decomposition in the tetragonal TiO2–SnO2 system on the basis of a nonlinear diffusion equation. A time evolution of the microstructure and the effect of coherent strain on the separated two phases were investigated by Langer's approximate method and the finite difference method. It was shown that the composition fluctuations develop in the first stage of the spinodal decomposition, and the formation of interface and the grain growth appear in the second stage. The local stress field and the local strain field with the coherence of the lattice were calculated. Subsequently the appearance of the interface dislocations in the (100) and (010) planes was demonstrated to occur in the third stage. Physical interpretation was given to the experimental observations for the tetragonal TiO2–SnO2 system on the basis of those calculations.
Electromechanical Properties of Some Pb (Mg1/3Nb2/3–PbTiO3–(Ba,Sr)TiO3 Ceramics: I
Authors: Pilgrim Steven M. , Massuda Mona , Prodey Jackie D. , Ritter Andrew P.
Published: March 2005

Compositional variation within the Pb(Mg1/3Nb2/3) O3–PbTiO3–(Ba, Sr)TiO3 (hereafter PMN–PT–BT,ST) ternary (6.4% PT% 14.1%, 1.25% BT,ST% 2.5%) results in major changes in induced strain and hysteresis. For the 1.25% BT family, the increase in strain correlates with an increase in Tmax, while the dielectric loss is uncorrelated with hysteresis and strain. In addition, weak field aging (which is not reset by application of field) shows little effect on strain and hysteresis for drive fields of > 0.2 MV/m. The vary narrow polarization‐fields loops (virgin curvesnearly indistinguishable from subsequent cycles) show that weak‐field permittivity is a good approximation to the high‐field permittivity. is a good approximation to the high‐field Permittivity. Although these data clarify the frequency (Tmax is linearly dependent on the logarithm of the frequency) effect on weak‐field dielectric behavior, they do not directly address the question of meaningful extrapolation of high‐field strain with frequency. In particular, the question remains as to whether the high‐field permittivity and strain are frequency dependent. In future papers we will address this question by a combination of measurement techniques as functions of frequency.
Pulsed‐Laser Deposition of Barium Titanate Thin Films
Authors: Norton M. Grant , Cracknell Kathryn P. B. , Carter C. Barry
Published: March 2005

Barium titanate (BaTiO3) thin films have been deposited on single‐crystal magnesia (MgO) substrates by pulsed‐laser ablation. Temperature dependence of capacitance measurements show a peak of 110°C, indicative that a ferroelectric phase transition has occurred at this temperature. This value is lower than that determined for single‐crystal BaTiO3, but consistent with that found for BaTiO3 thin films produced by other methods. It has been demonstrated that the microstructure of the films can be varied by changes in the deposition parameters. Optimizing these variations permits the formation of thin films with controlled microstructures and properties.
Role of Anion Vacancies in Nitrogen‐Stabilized Zirconia
Authors: Cheng Yi‐Bing , Thompson Derek P.
Published: March 2005

Introduction of nitrogen into zirconia creates oxygen vacancies in the anion sublattice as required by charge neutrality when N3− replaces for O2− in the structure, being similar to those obtained by lower valency cation substitution for zirconium. There is no essential structural difference between the cation‐related vacancy and the anion‐related vacancy, and their effects on the stabilization of zirconia are additive. The zirconia structure can, when formed in the Zi─Y─O─N system, tolerate a total of 6% of vacancies in the anion lattice without deviating from the original fluorite structure; above this limit, ZrN precipitates. Therefore, both partially and fully stabilized zirconia can dissolve a certain amount of nitrogen when these phases react with either atmospheric nitrogen or a solid nitride at high temperatures.
Alkali‐Resistant Magnesium Aluminosilicate Oxynitride Glasses
Authors: Steffestun Bärbel , Frischat Günther H.
Published: March 2005

Glasses containing up to 3.3 wt% nitrogen were prepared in the system MgO─Al2O3─SiO2─AIN─Si3N4. GlasGlass transition temperature, density, and elastic properties increased with increasing nitrogen content. Resistance against aqueous alkaline solutions was determined by weight loss measurements, solution and surface analysis. The good durability of both oxide and oxynitride glasses is caused by a protective surface layer. The introduction of nitrogen decreases the alkaline attack. The data suggest that nitrogen is incorporated as Si─N boxhs.
New Preparation Method for PZT Films Using Electrochemical Reduction
Authors: Matsumoto Yasumichi , Adachi Hideki , Hombo Jukichi
Published: March 2005

PZT perovskite films on stainless steel were prepared by electrochemical reduction in solutions containing TiO2+, ZrO2+, and Pb2+ ions. Heat treatment at temperatures higher than about 500°C was necessary for crystallization, because the as‐deposited oxide films were amorphous. The deposited oxides consisted of a mixture of hydroxides and oxide produced by an increase of pH due to some electrochemical reduction reactions of NO3−, H+, and H2O on the electrode surface. The composition of the PZT films was easily controlled by the composition in solution during the electrolysis. The mechanism of the PZT precursor deposition is discussed.
Core/Rim Structure of Liquid‐Phase‐Sintered Silicon Carbide
Authors: Sigl Lorenz S. , Kleebe Hans‐Joachim
Published: March 2005

Plasma etching in conjunction with scanning and analytical transmission electron microscopy was used to characterize the microstructure and microchemistry of silicon carbide sintered with yttrium‐aluminum garnet (YAG). The SiC grains comprise a core/rim structure with small amounts of excess yttrium, aluminum, and oxygen being present in the rim while these elements are missing in the core. The core/rim interface was found to be coherent, and both the core and the rim are composed of the same polytype, predominantly the 6H structure. These results suggest that Ostwald ripening by solution and reprecipitation controls the sintering mechanism in this system.
Simple Notch Preparation Technique for Fracture Toughness Measurements in Partially Stabilized Zirconia
Authors: Annamalai V. E. , Ponraj R. , Iyer S. Ramakrishna , Gokularathnam C. V. , Krishnamurthy R.
Published: March 2005

Fracture toughness is an important property of transformation‐toughening materials. Since indentation techniques are not reliable, notched‐beam techniques using slicing wheels on grinding machines are often used. Notching can induce residual stress as well as cracks, the effect of which cannot be completely nullified by annealing. Hence, the fracture toughness estimation methods may not yield realistic values for transformation‐toughening materials. The present paper reports on a reliable technique for notch preparation which can completely exclude the detrimental effects of stress/cracking that may arise due to notching, using slicing wheels on grinding machines.
Preparation of Spherical, Submicrometer Oxide Particles by Hydrolysis of Emulsified Alkoxide Droplets
Authors: Hardy Anne Bagley , Rhine Wendell E. , Bowen H. Kent
Published: March 2005

A new method for forming spherical, submicrometer ceramic oxide particles by the hydrolysis of emulsified alkoxide droplets is reported. Emulsions are formed of alkoxide droplets dispersed in an inert, polar solvent. The alkoxide droplets are hydrolyzed to form oxide particles by adding water to the emulsion. It was shown that individual droplets acted as “microreactors” and controlled the powder size, shape, and composition. Both single‐oxide and mixed‐oxide powders were formed by this technique.
Possible Electrical Double‐Layer Contribution to the Equilibrium Thickness of Intergranular Glass Films in Polycrystalline Ceramics
Authors: Clarke David R. , Shaw Thomas M. , Philipse Albert P. , Horn Roger G.
Published: March 2005

The plausibility of the entropic repulsion of electrical double layers acting to stabilize an equilibrium thickness of intergranular glass films in polycrystalline ceramics is explored. Estimates of the screening length, surface potential, and surface charge required to provide a repulsive force sufficiently large to balance the attractive van der Waals and capillary forces for observable thicknesses of intergranular film are calculated and do not appear to be beyond possibility. However, it has yet to be established whether crystalline particles in a liquid‐phase sintering medium possess an electrical double layer at high temperatures. If they do, such a surface charge layer may well have important consequences not only for liquid‐phase sintering but also for high‐frequency electrical properties and microwave sintering of ceramics containing a liquid phase.
Hydration of Calcium Aluminate Cements: A Solid‐State 27 Al NMR Study
Authors: Cong Xiandong , Kirkpatrick R. James
Published: March 2005

This paper presents the results of a study of the hydration of calcium monoaluminate (CA) and Lafarge Secar 71 (CA + CA2) using 27Al MAS and 1H‐27 Al CPMAS NMR spectroscopy. CPMAS, high H0 magnetic field strengths (11.7 T), and high MAS spinning speeds (13–14 kHz) provide significant new information about the Al structural environments present during hydration and about the mechanisms of hydration. Important results include the following: (1) Hydrated Al(4) and Al(6) environments are present during the incubation period. This observation is consistent with previously published hydration models. (2) The overall conversion of Al(4) in unhydrated phases to Al(6) in hydrated phases and the crystalline phases detected by XRD are similar to the results of previous studies. (3) There are previously undetected hydrated reaction intermediates present during the main reaction stage. At temperatures above 25°C this phase contains Al(4), and at 4°C it contains Al(4) and possibly Al(5). The incubation period observed for this reaction may be related to the nucleation of this phase.
Electrical Joining of Silicon Nitride Ceramics
Authors: Okuda Koji , Takai Hiroshi , Nishi Tokumitsu , Yanagida Hiroaki
Published: March 2005

The electrical joining of sintered Si3N4 ceramics by Joule heating was studied. A mixture of CaF2/kaolinite (70/30 wt%) with excellent electroheating characteristics and reactivity with Si3N4 ceramics was selected as a joining agent. The optimum conditions for electrical joining were determined using this joining agent. Analysis of the joint obtained under optimum conditions revealed that joining was accomplished by the formation of reaction zones and a joining layer through the mutual diffusion of the components in the joining agent and the sintering aids in the Si3N4. The joint layer was composed of a glassy substance consisting of Ca─Al─Si─Y─O─(F)─(N) and contained a few particles of β─Si3N4. Four‐point bend tests indicated that joined bodies could be obtained which maintained a strength of about 300 MPa up to 800°C. Finally, a comparative study was made with a joint obtained using furnace heating. These results indicated that the joints obtained using electrical joining were superior to those produced in the furnace.
Characterization of Calcium Lanthanum Oxalate Powders Coprecipitated from Different Binary Solvent Mixtures
Authors: Shen Ann‐Tinn , Lee Ying‐Sheng , Sungyu Nan‐Kuen
Published: March 2005

White amorphous powders of well‐mixed calcium and lanthanum oxalates were prepared by coprecipitation of calcium and lanthanum nitrates with 1M oxalic acid. SEM observation showed particle shapes of cubes, flakes, and agglomerates when water‐organic solvent mixtures were employed as the precipitation media. The measured specific surface area and the median particle diameter (D50) ranged between 1.5–76 m2/g and 0.9–14 μm, respectively, as a result of the divergent particle morphology. The morphology changes were attributed to a change of precipitation rate in different solvent mixtures. An attempt was made to explain the rate changes by the solvation energy change of ions which resulted in interfacial energy change within the depositing surface region.
Highly Oriented, Chemically Prepared Pb(Zr, Ti)O3 Thin Films
Authors: Tuttle Bruce A. , Voigt James A. , Goodnow David C. , Lamppa Diana L. , Headley Thomas J. , Eatough Michael O. , Zender Gary , Nasby Robert D. , Rodgers Steven M.
Published: March 2005

We have fabricated highly oriented, chemically prepared thin films of Pb(Zr0.04Tio.0.60)O3 (PZT 40/60) on both insulating and conducting substrates. While (100) MgO single crystals were used as the insulating substrates, the conducting substrates. were fabricated by RF magnetron sputter deposition of 100‐nm‐thick (100) Pt films onto (100) MgO substrates. For comparison, we also fabricated PZT 40/60 films that had no significant preferential orientation on platinized MgO substrates. Sputter deposition of an underlying amorphous Pt film was used to fabricate randomly oriented PZT 40/60 films. Highly (001) oriented PZT 40/60 films had higher remanent polarization (61 μC/cm2 compared to 41 μC/cm2) and lower relative dielectric constant (368 compared to 466) than PZT 40/60 films that were randomly oriented.
Densification of Large Pores: II, Driving Potentials and Kinetics
Authors: Slamovich Elliott B. , Lange Frederick F.
Published: March 2005

A kinetic analysis of densification is presented for the case of isolated, identical pores separated by dense, polyerystal‐line material where the grain size is a variable (smaller to larger, relative to the pore size). The analysis includes the influence of both grain growth and mass transport rates on the driving potential for mass transport to the pore. For the expected condition where the rate of grain growth is much greater than the rate of pore shrinkage, it is shown that the driving potential is relatively independent of pore surface curvature, and approaches (2γs/Rpo) sin (ψe/2) during grain growth, where γs is the surface energy per unit area of the material, ψe is the dihedral angle, and Rpo is the initial pore radius. Using this driving potential, an expression is derived for the current densification rate. The proposed mechanism for mass transport is radial diffusion through a spherical polycrystalline unit cell containing a spherical pore, where diffusion is restricted to grain boundaries that intersect the pore. The expression includes the average separation distance between pores and the grain boundary area intersecting each pore. This expression is in qualitative agreement for data reported in Part I for a Zr(3Y)O2 material where the grain size is always smaller than the pore size, and a Zr(8Y)O2 material where the grain size is larger than the pore size.
Effects of Temperature and Oxygen Partial Pressure on Nonstoichiometry of YBa2Cu3O6+δ
Authors: Lee Dong Nyung , Lee Byeong‐Joo
Published: March 2005

The oxygen content (6 +δ) in YBa2Cu3O6+δ varies with temperature and oxygen partial pressure. An equation for the content as a function of temperature and oxygen partial pressure has been obtained based on the two‐sublattice model of YBa2Cu3O6(V0, O)1. The results calculated using the equation are in very good agreement with published measured data.
Synthesis of Ba2RCu4O8 (R = Y, Sm) Superconductors at Oxygen Pressure of 1 atm by Spray‐Frozen/Freeze‐Drying Method
Authors: Matsuda Motohide , Ogawa Yoshihisa , Aihara Yasuhiko , Yamashita Kimihiro , Umegaki Takao
Published: March 2005

Precursor powders for high‐Tc Ba2RCu4O8 (R = Y, Sm) superconductors were successfully prepared through spray‐frozen/freeze‐drying (SF/FD) of a mixed aqueous solution that included the respective compounds according to the stoichiometric composition. These SF/FD powders were used to obtain ceramic superconductors composed of single‐phase orthorhombic Ba2RCu4O8 (R = Y, Sm) by sintering at an oxygen pressure of 1 atm. Critical temperatures measured were 84 K and 76 K for Ba2YCu4O8 and Ba2SmCu4O8, respectively, comparable to the previously reported values for these superconductors prepared under high oxygen pressure (100 atm). The present result was assumed attributable to the highly homogeneous powders.
Topotactically Oriented α‐Si3N4 Cores in Sintered β‐Si3N4
Authors: Krämer Martin
Published: March 2005

α‐Si3N4 core structures within β‐Si3N4 grains have been studied by transmission electron microscopy. The grains were dispersed in an oxynitride glass which was previously melted at 1600°C. The cores were topotactically related to the as‐grown β‐Si3N4 crystallites and are related to epitactical nucleation during heat treatment as the most probable mechanism.
Space Charge Segregation at Grain Boundaries in Titanium Dioxide: II, Model Experiments
Authors: Ikeda Jeri Ann S. , Chiang Yet‐Ming , Garratt‐Reed Anthony J. , Sande John B. Vander
Published: March 2005

A quantitative study of space charge solute segregation at grain boundaries in TiO2 is conducted, using a new STEM method for the measurement of aliovalent solute accumulation. It is shown that the electrostatic potential at grain boundaries can be varied in sign and magnitude with doping, oxygen pressure, and temperature, and that the isoelectric point lies in slightly donor‐doped compositions for samples annealed in air. The experimental results closely fit the space charge model in Part I. Space charge solute segregation is found even in defect regimes of high electron concentration. Approximately one in ten grain boundaries are “special” in exhibiting no detectable segregation; in one such instance a twin boundary is identified. Among boundaries with significant amounts of segregation, clear differences in potential also exist. From the potential determined in acceptor‐ and donor‐doped compositions, the Frenkel energy (assumed to be lower than the Schottky energy in TiO2) can be separated into its individual terms. An average value for the titanium vacancy formation energy of gvTi= 2.4 eV and an upper limit to the titanium interstitial formation energy of gTii= 2.6 eV are obtained.
New Yellow Ceramic Pigment Based on Codoping Pyrochlore‐type Y2Ti2O7 with V5+ and Ca2+
Authors: Ishida Shingo , Ren Feng , Takeuchi Nobuyuki
Published: March 2005

A new yellow pigment with the pyrochlore structure CaxY2−xVxTi2−xO7 was prepared as a substitute for the decreasing variety of available yellow ceramic pigments due to the severe regulation of toxic lead and cadmium. The solubility limit of vanadium in this pigment was found to be 1.5 wt% as V2O5 or 0.13 as x in the above formula expression. Characterization of vanadium in the vanadium pyrochlore yellow pigment by electron spectroscopy for chemical analysis and electron spin resonance showed that the oxidation state of vanadium was V5+ and its yellow color mostly originated from V5+ substituted for Ti4+. Comparison of color characteristics of CaxY2−xVxTi2−xO7 with those of commercial V–SnO2 and V–ZrO2 revealed that CaxY2−xVxTi2−O7 had better color strength and brightness than the commercial pigments.
Preparation and Optical Properties of Transparent Glass‐Ceramics Containing Cobalt(ll) Ions
Authors: Tanaka Katsuhisa , Mukai Takash , Ishihara Tsuguo , Hirao Kazuyuki , Soga Naohiro , Sogo Seiji , Ashida Masaaki , Kato Riso
Published: March 2005

Transparent glass‐ceramics containing ZnAl2O4:Co2+ and LiGa5O8:Co2+ crystallites have been prepared by heat treatment of glasses in the zinc aluminosilicate and lithium gallate silicate systems, respectively. Crystalline LiGa5O8 was already precipitated in an as‐prepared specimen, while ZnAl2O4:Co2+ precipitated from the glass upon heat treatment. The crystallite size varies from about 5 to 20 nm with increasing heat treatment temperature for both systems, and glass‐ceramics containing crystallites of less than about 10 nm are transparent. The low‐temperature optical absorption and emission spectra are compared with those of single crystals, indicating that almost all of the Co2+ ions replace Zn2+ ions in the ZnAl2O4 system, while some of the Co2+ ions are incorporated into the LiGa3O8 system, although the amount of Co2+ which remains in the glass matrix is rather large in the latter system.
Diffusionless Tetragonal–Cubic Transformation Temperature in Zirconia–Ceria Solid Solutions
Authors: Yashima Masatomo , Morimoto Kenji , Ishizawa Nobuo , Yoshimura Masahiro
Published: March 2005

Diffusionless tetragonal (t′)  cubic (c′) phase transformation in 65‐mol%‐CeO2‐ZrO2 was investigated around the c′‐t′ equilibrium temperature T0c′‐t′ using powder X‐ray diffraction, where c′ was defined as a tetragonal or cubic phase with an axial ratio of unity. The {400} peak profile of t′‐ZrO2 broadened at 860° and 900°C. This indicated that the t′‐ZrO2 transformed partially into c′‐ZrO2. The {400} peak profile of c′‐ZrO2 also broadened at 860° and 900°C, which indicated that the c′‐ZrO2 partially transformed to t′‐ZrO2. The finish point of t′→c′ transformation Tft′→c′ was investigated by annealing the t′‐ZrO2 containing 30–65 mol% CeO2 at various temperatures. The T′ft′→c′ line existed in the vicinity of the cubic solubility limit within the t + c two‐phase region. This Tft′→c′ location, which should have been located in the vicinity of T0c′‐t′ could not be explained by a simple regular solution model. However, it was described successfully by a thermodynamic model based on Landau's phenomenologic theory.
Effect of Sintering Aids on Microstructures and PTCR Characteristics of (Sr0.2Ba0.8)TiO3 Ceramics
Authors: Cheng Hsiu‐Fung , Lin Tsai‐Fa , Hu Chen‐Ti , Lin I‐Nan
Published: March 2005

The effects of liquid‐phase sintering aids on the microstructures and PTCR characteristics of (Sr0.2Ba0.8)TiO3 materials have been studied. The grain size of sintered materials monotonically decreases with increasing content of Al2O3–SiO2–TiO2 (AST). The ultimate PTCR properties with ρht/ρrt as great as 105.61 are obtained for fine‐grain (10‐μm) samples, which contain 12.5 mol% AST and were sintered at 1350°C for 1.5 h. The quantity of liquid phase formed due to eutectic reaction between AST and (Sr,Ba)TiO3 is presumably the prime factor in determining the grain size of samples. The grains grow rapidly at the sintering temperature in the first stage until the liquid phase residing at the grain boundaries reaches certain critical thickness such that the liquid–solid interfacial energy dominates the mechanism of grain growth.