bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure of Alumina Composites Containing Niobium and Niobium Aluminides
Authors: Scheu Christina , Dehm Gerhard , Kaplan Wayne D. , García Daniel E. , Claussen Nils
Published: July 2010

The microstructures of niobium‐based alumina composites prepared by pressureless sintering of compacts of attrition milled Al2O3, Nb, and Al powder mixtures were studied. The addition of a small amount of Al is assumed to assist in rapid sintering. X‐ray diffraction analyses show that Al2O3, Nb, NbO, and the intermetallics AlNb2 and AlNb3 are present in the composites. Electron microscopy studies confirm the existence of these phases and reveal dense, fine‐grained (≤500 nm) composites. Al2O3 and Nb grains form the matrix. NbO occurs as grains and additionally as small particles within Al2O3 grains and at Al2O3/Al2O3 grain boundaries. The intermetallic AlNb2 and AlNb3 phases do not exceed 300 nm in size if they occur at grain boundaries, and possess even smaller dimensions when occluded within Al2O3 grains or located at Al2O3 triple junctions. While the niobium intermetallics are expected to form during the heating cycle before reaching the sintering temperature, the NbO is assumed to form during the cooling cycle due to precipitation of oxygen dissolved in the niobium.
Role of Defects on the Aging Behavior of Manganese‐Doped Lead Iron Tungstate Relaxor Ceramics
Authors: Zhou Liqin , Vilarinho Paula M. , Baptista João Lopes
Published: July 2010

The effect of oxygen annealing on the dielectric aging of manganese‐doped Pb(Fe2/3W1/3)O3 (PFW) ceramics is investigated in an attempt to clarify the role of defects on aging. Evident relaxor‐type aging is observed in as‐sintered manganese‐doped PFW samples. The degree of aging gradually decreases as the annealing time increases, and no aging is observed for 100 h of annealing, which supports the correlation between oxygen vacancies and aging.
Inclusions of Nanometer‐Sized Al2O3 Particles in a Crystalline (Sc,Lu)2(WO4)3 Matrix
Authors: Imanaka Nobuhito , Köhler Joachim , Masui Toshiyuki , Adachi Gin‐ya , Taguchi Eiji , Mori Hirotaro
Published: July 2010

Nanometer‐sized Al2O3 particles were successfully synthesized as crystalline inclusions by mixing both components to form the nanometer‐sized particles and the (Sc,Lu)2(WO4)3 matrices in a crystal lattice by preparing a solid solution of (Sc,Lu)2(WO4)3 and Al2(MoO4)3 and then decomposing the solid solution. The particles were dispersed uniformly and without agglomeration, which is commonly observed with conventional preparation techniques. The average particle size of the Al2O3 was 3.5 nm, and the standard deviation was estimated to be 1.1 nm.
Mechanochemical Synthesis of Lanthanum Aluminate by Grinding Lanthanum Oxide with Transition Alumina
Authors: Zhang Qiwu , Saito Fumio
Published: July 2010

Grinding lanthanum oxide (La2O3) with Al2O3 was conducted to investigate their mechanochemical reactions to form lanthanum aluminate (LaAlO3) powder using a planetary ball mill. Grinding for 120 min allowed us to obtain single‐phase LaAlO3 with a large surface area when transition alumina was used, whereas no formation of LaAlO3 was achieved when α‐Al2O3 was used. The mechanochemical process can be applied to synthesize other rare‐earth (RE) aluminates (REAlO3) from mixtures of a rare‐earth oxide and transition alumina.
Comparison of R‐Curves from Single‐Edge V‐Notched‐Beam (SEVNB) and Surface‐Crack‐in‐Flexure (SCF) Fracture‐Toughness Test Methods on Multilayered Alumina–Zirconia Composites
Authors: Moon Robert , Bowman Keith , Trumble Kevin , Rödel Jürgen
Published: July 2010

The single‐edge V‐notched‐beam fracture testing method was used to measure the short‐crack R‐curve behavior of a 90‐vol%‐alumina–10‐vol%‐ceria‐doped zirconia multilayered composite. The initiation and extension of short cracks from the V‐notch tip were observed in situ via optical microscopy. Initial crack lengths of 15–50 μm were obtained repeatedly. The resulting R‐curve was similar to the R‐curve that was measured using the surface‐crack‐in‐flexure testing method. The ability to control the position of the V‐notch tip within a material permits study of the influence of specific microscopic features on the fracture behavior.
Transformation Toughening in Zirconia‐Containing Ceramics
Authors: Hannink Richard H. J. , Kelly Patrick M. , Muddle Barry C.
Published: July 2010

The recognition of the potential for enhanced fracture toughness that can be derived from controlled, stress‐activated tetragonal (t) to monoclinic (m) transformation in ZrO2‐based ceramics ushered in a new era in the development of the mechanical properties of engineering ceramics and provided a major impetus for broader‐ranging research into the toughening mechanisms available to enhance the fracture properties of brittle‐matrix materials. ZrO2‐based systems have remained a major focal point for research as developments in understanding of the crystallography of thet→mtransformation have led to more‐complete descriptions of the origins of transformation toughening and definition of the features required of a transformation‐toughening system. In parallel, there have been significant advances in the design and control of microstructure required to optimize mechanical properties in materials developed commercially. This review concentrates on the science of thet→mtransformation in ZrO2and its application in the modeling of transformation‐toughening behavior, while also summarizing the microstructural control needed to use the benefits in ZrO2‐toughened ceramics.
Effect of Nickel Oxide/Yttria‐Stabilized Zirconia Anode Precursor Sintering Temperature on the Properties of Solid Oxide Fuel Cells
Authors: Primdahl Søren , Sørensen Bent F. , Mogensen Mogens
Published: July 2010

An NiO/yttria‐stabilized zirconia (YSZ) layer sintered at temperatures between 1100° and 1500°C onto dense YSZ electrolyte foils forms the precursor structure for a porous Ni/YSZ cermet anode for solid oxide fuel cells. Conflicting requirements for the electrochemical performance and mechanical strength of such cells are investigated. A minimum polarization resistance of 0.09 Ω.cm2at 1000°C in moist hydrogen is obtained for sintering temperatures of 1300°–1400°C. The mechanical strength of the cells decreases with increased sintering temperature because of the formation of channel cracks in the electrode layers, originating in a thermal expansion coefficient mismatch between the layers.
Synthesis of Dense Lead Titanate Ceramics with Submicrometer Grains by Spark Plasma Sintering
Authors: Takeuchi Tomonari , Tabuchi Mitsuharu , Kondoh Isao , Tamari Nobuyuki , Kageyama Hiroyuki
Published: July 2010

Dense PbTiO3 ceramics consisting of submicrometer‐sized grains were prepared using the spark‐plasma‐sintering (SPS) method. Hydrothermally prepared PbTiO3 (0.1 μm) was used as a starting powder. The powder was densified to ≳98% of the theoretical X‐ray density by the SPS process. The average grain size of the spark‐plasma‐sintered ceramics (SPS ceramics) was ≲1 μm, even after sintering at 900°–1100°C, because of the short sintering period (1–3 min). The measured permittivity of the SPS ceramics showed almost no frequency dependence over the range 101–106 Hz, mainly because pores were absent from the ceramics. The coercive field of the SPS ceramics was somewhat higher than that of conventionally sintered ceramics, which could be attributed to the small‐grained microstructures of the SPS ceramics.
Fractal Analysis of Toughening Behavior in 3BaO.5SiO2Glass‐Ceramics
Authors: Hill Thomas J. , Mecholsky John J. , Anusavice Kenneth J.
Published: July 2010

The objective of this paper was to analyze the crystal aspect ratio (AR), the fracture toughness, and the fractal dimension of 3BaO.5SiO2 glass‐ceramics and to relate the topography of fracture surfaces to fractal behavior. These analyses demonstrate that crystal morphology strongly affects the fracture path, the fracture toughness, and the fractal dimension. Fracture toughness increased from 0.7 ± 0.1 MPa.m1/2 for the glass to 2.2 ± 0.6 MPa.m1/2for the glass‐ceramic with an AR of 8.1 while the fractal dimensional increment (D*) for the glass and the glass‐ceramic increased from 0.10 ± 0.01 to 0.25 ± 0.02, respectively. The materials with lower aspect ratios (AR = 1.4 and 3.6) exhibited the predicted relationship between toughness and D* while the glass‐ceramic with an aspect ratio of 8.1 did not satisfy the expected relationship because of multiple toughening mechanisms.
Effect of Atmospheric Humidity on the Fatigue Crack Propagation Behavior of Short Cracks in Silicon Nitride
Authors: Ishihara Sotomi , McEvily Arthur J. , Goshima Takahito
Published: July 2010

The effect of the environment on crack‐growth processes in silicon nitride was studied by investigating the static and fatigue crack‐growth behavior of small surface cracks, as influenced by testing (i) in the ambient environment, (ii) in distilled water, (iii) under vacuum, and (iv) in toluene. A principal finding was that testing under cyclic conditions led to crack‐growth rates that were much higher in air than in toluene, whereas testing under static conditions in air or toluene led to minor differences in the rate of static fatigue crack growth. This difference in sensitivity to the environment under static and cyclic loading conditions was attributed, in part, to a much‐greater extent of microcracking at the surface ahead of the main crack in air under cyclic conditions, in comparison to that in other environments. This propensity for microcracking at the surface in air under cyclic conditions also was reflected in the aspect ratios of the crack shapes that developed.
Effects of Pores on Mechanical Properties of Plasma‐Sprayed Ceramic Coatings
Authors: Nakamura Toshio , Qian G. , Berndt Christopher C.
Published: July 2010

The effects of pore sizes, shapes, and orientations on the mechanical properties of thermally sprayed ceramic coatings are investigated. The analysis is conducted using detailed finite‐element models with geometries similar to those of actual ceramic coatings containing many embedded pores. These microstructural models include many randomly placed pores of different sizes and shapes and are loaded in tension to determine their effective elastic moduli along the spray and transverse directions. We modeled coatings with statistical distributions of pore sizes and shapes that followed those of actual Al2O3–TiO2 coatings. Because the pores in such a model are of different sizes and shapes, the model must be large enough to contain sufficient pores before the average modulus obtained from uniaxial loading can be identified as an effective property. Using differently sized models, we determined the variability of the average moduli. Such information is valuable when homogenized or continuum material models are used in the stress analyses of coatings. Our computed results show that a model must be large enough to contain 50–100 pores before the averaging of properties is accurate. Using the Al2O3–TiO2 models, we also simulated microindentation tests. Unlike the results determined from uniaxial loading, the elastic moduli estimated from indentation possessed large variations. Apparently, the morphology of the pores immediately beneath the indentation or within the zone of influence has a significant effect on the response of the indenter and the measured modulus. The implications of these results and the computational capability to predict the mechanical properties of porous, plasma‐sprayed ceramic coatings are discussed here.
Fracture and Subcritical Crack‐Growth Behavior of Y‐Si‐Al‐O‐N Glasses and Si3N4 Ceramics
Authors: Bhatnagar Ajay , Hoffman Michael J. , Dauskardt Reinhold H.
Published: July 2010

Fracture and environmentally assisted subcritical crack‐growth processes are examined in bulk Y‐Si‐Al‐O‐N oxynitride glasses with compositions typical of the grain boundary phase of silicon nitride ceramics. Both long‐crack (in compact tension specimens) as well as short‐crack behavior (using indentation techniques) were investigated to establish a reliable fracture toughness and to elucidate the anomalous densification behavior of the oxynitride glass. Environmentally assisted subcritical crack‐growth processes were studied in inert, moist, and wet environments under both cyclic and static loading conditions. Behavior is discussed in terms of the interaction of the environment with the crack tip. Likely mechanisms for environmentally assisted crack growth are discussed and related to the subcritical crack‐growth behavior of silicon nitride ceramics.
Crystallization in 70Ga2S3.30La2S3(mol%) Glasses as a Function of Oxide/Hydroxide Concentration
Authors: Morgan Sean P. , Reaney Ian M. , Buckley Robert , Furniss David , Seddon Angela B.
Published: July 2010

The crystallization of 70Ga2S3.30La2S3(mol%) glasses has been studied using X‐ray diffraction and transmission electron microscopy. Two of the glasses were prepared from raw materials with nominally different oxide concentrations. The third was prepared from raw materials aged in an oxygen‐depleted, argon‐flushed glove box for more than 1 yr. Their oxide/hydroxide impurity content was qualitatively ranked using Fourier transform infrared spectroscopy. The lowest oxide content composition (≤0.5 wt%, supplied information) devitrified readily close to the glass transition temperature, Tg, forming crystallites of a new (GLS) phase with a monoclinic Bravais lattice and a lathlike internal structure. Ga2S3was observed in small quantities between the laths. Samples prepared from nonaged, high oxide (1–3 wt%) content precursors produced the most stable glass. On crystallization, these samples exhibited spherulites composed of intergrown laths of melilite‐structured La3.33Ga6S14and the new monoclinic GLS phase. Whiskers of Ga2S3were found in the residual glass between crystallites. Samples prepared from aged raw materials produced spherulites of La3.33Ga6S14on crystallization with no identifiable regions of the new GLS phase.
Deformation Mechanism of Fine‐Grained Magnesium Aluminate Spinel Prepared Using an Alkoxide Precursor
Authors: Shiono Takeshi , Ishitomi Hiroyuki , Okamoto Yasunori , Nishida Toshiko
Published: July 2010

Polycrystalline MgAl2O4 spinel with high purity and stoichiometric composition was prepared using alkoxide precursors. The average grain size of the polycrystal was fine (1.7 μm). The deformation mechanism of the polycrystal was investigated in air at temperatures of 1300°–1400°C. At 1300°C, oxygen lattice diffusion controlled the deformation, despite the fine grain size; however, increases in the temperature and applied stress caused cavities to nucleate and grow. Spinel possessed better creep resistance than alumina of comparative grain size. The effective diffusion coefficient was determined as follows: [formula omitted]
Mixed‐Alkali Effect on Rayleigh Scattering in K2O–Na2O–MgO–SiO2 Glasses
Authors: Tsujikawa Kyozo , Ohashi Masaharu
Published: July 2010

The Rayleigh scattering of the mixed‐alkali glass system K2O–Na2O–MgO–SiO2 (KNMS) was investigated, both experimentally and theoretically. The lowest Rayleigh scattering coefficient (38% of that for pure SiO2 glass) was obtained when the glass composition was 22K2O–8Na2O–10MgO–60SiO2 (in mol%). These values are equal to or less than the minimum values reported for the ternary sodium silicate glass Na2O–MgO–SiO2. The Rayleigh scattering caused by concentration fluctuation was believed to have been reduced greatly in this KNMS glass, because the mobility of the alkali‐metal ions was reduced by the mixed‐alkali effect.
Indentation Crack Length Anisotropy in Silicon Nitride with Aligned Reinforcing Grains
Authors: Park Dong‐Soo , Kim Chang‐Won
Published: July 2010

Vickers indentation was performed on surfaces of silicon nitride with an aligned microstructure in order to study the interaction between cracks and the microstructure. Although there was not much evidence of crack bridging, the transverse radial cracks were very short, resulting in high fracture toughness values. The longitudinal radial cracks tended to propagate along the grain boundary of the reinforcements and were much longer than the transverse cracks. As the sintering temperature increased, the lateral cracks on the casting surface led to spalling and consumed more energy for the crack formation, making the longitudinal cracks shorter. On the surface normal to the alignment direction, there was no spalling and the indentation cracks became longer as the sintering temperature increased.
Differences in Tensile and Bending Strength for Knoop‐Cracked Lead Zirconate Titanate Specimens
Authors: Fett Theo , Munz Dietrich , Thun Gerhard
Published: July 2010

The strength of piezoelectric ceramics differs greatly in tension and bending tests. This effect, which is known to occur for specimens with a natural flaw population, also occurs in tests that involve Knoop‐cracked specimens. In such samples, the linear‐elastically computed bending strength is ∼35% higher than the tensile strength. Computation of the actual stress distribution in the bending bars has shown that these differences are predominantly caused by the nonlinearity and nonsymmetry of the deformation behavior.
Sintering Behavior of Nanocrystalline Zirconia Prepared by Chemical Vapor Synthesis
Authors: Srdić Vladimir V. , Winterer Markus , Hahn Horst
Published: July 2010

Powder synthesis and ceramic processing methods have to be improved to take full advantages of new, improved properties of nanocrystalline ceramics. Sintered nanocrystalline ceramics of pure, undoped zirconia are formed from nanocrystalline powder of optimized quality obtained by the chemical vapor synthesis (CVS) method. The as‐synthesized CVS ZrO2 powder is nonagglomerated with a crystallite size of about 5 nm, narrow size distribution, and high crystallinity. On uniaxial compaction a transparent green body of ultrafine, uniform microstructure and narrow pore size distribution corresponding to the grain size distribution is formed, which is sintered under vacuum at 950°C into a transparent, fully dense ZrO2 ceramic with a grain size of 60 nm.
Mullite Decomposition Kinetics and Melt Stabilization in the Temperature Range 1900—2000°C
Authors: Xiao Zhijun , Mitchell Brian S.
Published: July 2010

An investigation of the mullite decomposition mechanism and kinetics in the temperature range 1900—2000°C was conducted. SEM‐EDS and XRD analysis showed that the decomposition of mullite in this temperature range was primarily caused by the presence of carbon from furnace components. A reaction mechanism, in which gas‐phase SiO2 reacts with carbon to form SiO and CO, is proposed; both IR analysis and kinetic studies support the proposed mechanism. The decomposition was completely suppressed by the introduction of a modified crucible assembly and the addition of excess SiO2 to the reaction system. A mullite melt of stable composition was thus obtained, setting the groundwork for inviscid melt spinning mullite fiber making process development.
Elastic‐Property Measurements on CVI SiC/SiC Minicomposites by Acoustic Microscopy
Authors: Cros Bernard , Combette Philippe , Attal Jacques
Published: July 2010

In situ elastic properties of the fiber and matrix in composites obtained via chemical vapor infiltration/chemical vapor deposition (CVI‐CVD) have been determined using acoustic microscopy. An unusually high frequency was used to attain the resolution that was required by the structure and small size of the constituents in these nonhomogeneous materials. A coupling liquid was prepared with acoustic properties that were chosen with consideration of the high frequency and the material characteristics. Local measurements on the fibers and matrix were achieved by studying the acoustic signature that was processed on very small areas. The elastic modulus of the fibers and matrices was deduced from the velocity measurements.
Synthesis and Characterization of Ti3AlC2
Authors: Tzenov Nikolay V. , Barsoum Michel W.
Published: July 2010

Polycrystalline bulk samples of Ti3Al1.1C1.8 have been fabricated by reactively hot isostatically pressing a mixture of titanium, graphite, and Al4C3 powders at a pressure of 70 MPa and temperature of 1400°C for 16 h. The hot isostatically pressed samples are predominantly single phase (containing ∼4 vol% Al2O3), fully dense, and have a grain size of ∼25 μm. This carbide is similar to Ti3SiC2, with which it is isostructural, and has an unusual combination of properties. It is relatively soft (Vickers hardness of ∼3.5 GPa) and elastically stiff (Young's modulus of 297 GPa and shear modulus of 124 GPa); yet, it is lightweight (density of 4.2 g/cm3) and easily machinable. The room‐temperature electrical resistivity is 0.35 ± 0.03 μΩ·m and decreases linearly as the temperature decreases. The temperature coefficient of resistivity is 0.0031 K−1. The coefficient of thermal expansion, in the temperature range of 25°—1200°C, is 9.0 (± 0.2) × 10−6 K−1. The room‐temperature compressive and flexural strengths are 560 ± 20 and 375 ± 15 MPa, respectively. In contrast to flexure, where the failure is brittle, the failure in compression is noncatastrophic and is accompanied by some plasticity. The origin of that plasticity is believed to be the formation of a “shear” band that is oriented at an angle of ∼45° to the applied load. Ti3Al1.1C1.8 also is a highly damage‐tolerant material; a 10‐kg‐load Vickers indentation made in a bar 1.5 mm thick reduces the post‐indentation flexural strength by ∼7%. This material also is quite resistant to thermal shock. At temperatures of >1000°C, the deformation in compression is accompanied by significant plasticity and very respectable ultimate compressive stresses (200 MPa at 1200°C).
Alumina Dissolution into Silicate Slag
Authors: Zhang Shaowei , Rezaie Hamid Reza , Sarpoolaky Hossain , Lee William Edward
Published: July 2010

Dissolution of commercial white fused and tabular Al2O3 grains into a model silicate slag was investigated after 1 h at 1450° and 1600°C. Formation of CA6 and hercynitic spinel layers was observed at all Al2O3/slag interfaces. The spinel layer was not always continuous, and so, compared with the CA6 layer, it had a less‐significant effect on the dissolution process. The CA6 layer that formed adjacent to the tabular Al2O3 was incomplete at both temperatures, so that its dissolution was not a totally indirect process. These incomplete CA6 and spinel layers meant that slag penetrated into the tabular Al2O3 grains, which, thus, were corroded and disintegrated by the penetrating slag. There was evidence of liquid in the CA6 layer adjacent to the fused Al2O3 after 1 h at 1450°C, which also enabled direct dissolution. After 1 h at 1600°C, fused Al2O3 revealed a thick (∼60 μm), continuous and unpene‐trated CA6 layer, indicating fully indirect dissolution at this temperature.
Thermodynamic Optimization of the Silver—Bismuth—Strontium—Calcium—Copper—Oxygen (Ag‐Bi‐Sr‐Ca‐Cu‐O) System
Authors: Assal Jérôme , Hallstedt Bengt , Gauckler Ludwig J.
Published: July 2010

Experimental data on the phase equilibria between the high‐critical‐temperature (high‐Tc) superconducting compound 2212 and silver have been reviewed and assessed. Using these data, the interaction parameter of the Gibbs energy function of the liquid phase was optimized via the CALPHAD method. The calculation yields very good agreement with the experiment. This work is the final step in the optimization of the Ag‐Bi‐Sr‐Ca‐Cu‐O system.
Ternary System Al2O3—MgO—CaO: Part II, Phase Relationships in the Subsystem Al2O3—MgAl2O4—CaAl4O7
Authors: de Aza Antonio H. , Iglesias Juan E. , Pena Pilar , De Aza Salvador
Published: July 2010

Solid‐state compatibility and melting relationships in the subsystem Al2O3—MgAl2O4—CaAl4O7 were studied by firing and quenching selected samples located in the isopletal section (CaO·MgO)—Al2O3. The samples then were examined using X‐ray diffractomtery, optical microscopy, and scanning and transmission electron microscopies with wavelength‐ and energy‐dispersive spectroscopies, respectively. The temperature, composition, and character of the ternary invariant points of the subsystem were established. The existence of two new ternary phases (Ca2Mg2Al28O46 and CaMg2Al16O27) was confirmed, and the composition, temperature, and peritectic character of their melting points were determined. The isothermal sections at 1650°, 1750°, and 1840°C of this subsystem were plotted, and the solid‐solution ranges of CaAl4O7, CaAl12O19, MgAl2O4, Ca2Mg2Al28O46, and CaMg2Al16O27 were determined at various temperatures. The experimental data obtained in this investigation, those reported in Part I of this work, and those found in the literature were used to establish the projection of the liquidus surface of the ternary system Al2O3—MgO—CaO.
Precipitation of Magnesium Aluminum Spinel from Alumina‐Matrix Solid Solution: I, Fundamental Concept and Precipitation Behavior
Authors: Wang Yucong , Fujimoto Tetsuro , Maruyama Hiroshi , Koga Kazunori
Published: July 2010

Al2O3 ceramics with magnesium aluminum spinel dispersion particulates were produced by a precipitation treatment of Al2O3‐matrix solid solution, (Al1—2x,Tix,Mgx)2O3. We successfully constructed the precipitation process for synthesizing the nanocomposite, using the solubility dependence of titanium and magnesium in Al2O3 on the valence of titanium. Changing of the valence of titanium from 4+ to 3+ was accomplished by controlling the heating atmosphere, and, thereby, magnesium precipitation was promoted. The precipitation behavior was characterized using X‐ray diffractometry, and the microstructure was observed using transmission electron microscopy. We confirmed that magnesium aluminum spinel nanosized particulate were precipitated in the Al2O3 grain.
Dielectric and Structural Characteristics in Barium Lanthanum Magnesium Niobate
Authors: Lee Hwack Joo , Park Hyun Min , Cho Yang Koo , Ryu Hyun , Paik Jong Hoo , Nahm Sahn , Byun Jae‐Dong
Published: July 2010

The dielectric properties and their related microstructural characteristics in solid solutions of (1 —x)Ba(Mg1/3Nb2/3)O3 (BMN)—xLa(Mg2/3Nb1/3)O3 (LMN) (BLMN) were investigated by measuring the relative permittivity (ɛr), Q value, and temperature coefficient of resonator frequency (τf), and by observing the microstructure using transmission electron microscopy. The trend of variation of the temperature coefficient of the dielectric permittivity (τɛ) was the same for our solid solutions as that reported by Reaney et al. When the tolerance factor (t) was >1.01 in BLMN with composition x= 0 to 1.0, where the tilting of oxygen octahedra was not involved, the components of the microstructure included a disordered and transition phase as well 1:1 and 1:2 ordered phases. In the region where 1.01 < t < 0.96 with x= 0.2 to 0.7, the 1:1 order, the disorder, and the phase due to the antiphase tilting of oxygen octahedra were present. Finally, in the region where t < 0.96 with x= 0.7 to 1.0, the microstructure of BLMN was the same as that of the pure LMN, including the 1:1 order and the antiphase, inphase tilting of oxygen octahedra, and the antiparallel shift of A‐site cations.
Microstructure of Lanthanum Magnesium Niobate at Elevated Temperature
Authors: Lee Hwack Joo , Park Hyun Min , Cho Yang Koo , Ryu Hyun , Paik Jong Hoo , Nahm Sahn , Byun Jae‐Dong
Published: July 2010

Microstructural studies of the complex perovskite compound La(Mg2/3Nb1/3)O3 (LMN) were conducted using transmission electron microscopy (TEM) and X‐ray diffractometry (XRD) at elevated temperatures. 1:1 chemical ordering of B‐site cations and tilting of oxygen octahedra were observed in LMN. Three types of superlattice reflections, [1—2]{111}, [1—2]{110}, and [1—2]{100} were observed at room temperature and at 800°C in electron diffraction patterns. In the XRD experiments, the [1—2]{210} and [1—2]{300} extra peaks disappeared at temperatures >1200°C. However, the intensity of the superlattice [1—2]{111} peak did not change with increased temperature up to 1400°C. These results strongly indicated that the origin of superlattice reflection [1—2]{111} was different from that of the other superlattice reflections. It was mainly caused by the 1:1 chemical ordering of magnesium and niobium atoms. The TEM image observed at 800°C showed the ordered domain structures separated by the antiphase boundaries.
Electrical Properties of the Ta‐RuO2 Diffusion Barrier for High‐Density Memory Devices
Authors: Yoon Dong‐Soo , Baik Hong Koo , Lee Sung‐Man
Published: July 2010

The electrical properties of a Ta layer prepared with and without RuO2 addition were investigated. The Ta + RuO2/TiSi2/poly‐Si/SiO2/Si contact system exhibited lower total resistance and ohmic characteristics up to 800°C. Meanwhile, the Ta/TiSi2/poly‐Si/SiO2/Si contact system showed higher total resistance and nonohmic behavior after annealing at 650°C, attributed to the oxidation of both Ta and TiSi2 layers. In the former case, a Ta + RuO2 diffusion barrier showed an amorphous Ta microstructure and embedded RuOx nanocrystals in the as‐deposited state. The conductive RuO2 crystalline phase in the Ta + RuO2 film was formed by reaction between the nanocrystalline RuOx and oxygen indiffused from air during annealing. When the Ta layer was deposited with RuO2 addition, therefore, both the electrical properties and the oxidation resistance of the Ta + RuO2 diffusion barrier were better than those of TiN, TaN, and Ta‐Si‐N barriers.
Synthesis of Cerium(IV) Oxide Ultrafine Particles by Solid‐State Reactions
Authors: Yu Xianghua , Li Feng , Ye Xiangrong , Xin Xinquan , Xue Ziling
Published: July 2010

CeO2 ultrafine particles were prepared by solid‐state reactions at room temperature. These particles were found to have very fine particle sizes (∼3 nm) with a fluorite structure (a= 5.42 Å). BET measurements showed that the surface area of the particles was 96.2 m2/g. The use of two different precursors was found to affect the size of the CeO2 particles. We discuss the effect of calcination at different temperatures on the morphology, size, and BET surface area of CeO2 particles. A salt byproduct coating prevented agglomeration of the CeO2 particles.
Influence of Grain Size on the Indentation‐Fatigue Behavior of Alumina
Authors: Li Ming , Reece Michael J.
Published: July 2010

The surface fracture behavior of a high‐purity, high‐density alumina, as a function of grain size (3, 5, and 9 μm), was investigated using an indentation‐fatigue technique. Increasing the grain size reduced the threshold for crack nucleation, reduced the resistance to surface spalling, and increased the volume of materials lost per spalling event. These results are explained in terms of residual stresses and fatigue damage.
Measurement of Densification of Zinc Oxide Compacts Using an Optical, Noncontact, Noninvasive Extensometer
Authors: Olorunyolemi Tayo , Tolbert Renee , Wilson Otto , Carmel Yuval , Lloyd Isabel , Xu Gengfu , Jaworski Allen
Published: July 2010

An optical noninvasive, noncontact extensometer was used to measure the shrinkage of zinc oxide powder compacts during sintering. Powder compacts were uniaxially and isostatically pressed from micrometer, submicrometer, and nano powders and sintered in a thermal oven at temperatures up to 1100°C. The nanometer‐size sample started to densify at ∼400°C, about 200°C below the densification threshold of the micrometer‐size sample. The results are in good agreement with those obtained using a contact dilatometer.
Ferromagnetism and Magnetoresistance in La0.67Sr0.33Fe0.07Mn0.93O3
Authors: Li Ya‐Dong , Zhang Jiang‐Hui , Xiong Cao‐Shui , Liao Hong‐Wei
Published: July 2010

A bulk ceramic sample La0.67Sr0.33Fe0.07Mn0.93O3 (LSFMO) with a rhombohedral structure has been prepared from a coprecipitated carbonate precursor in this study. Ferromagnetism and a negative, isotropic magnetoresistance (MR) as large as 11% have been observed in a ceramic sample of LSFMO. There are two resistivity transition peaks on the resistivity versus temperature curves. The resistivity peak and MR have been related to the ferromagnetic state in LSFMO.
Production of Functionally Graded Materials from Electrochemically Modified Carbon Preforms
Authors: Jedamzik Ralf , Neubrand Achim , Rödel Juergen
Published: July 2010

A new process based on carbon as a precursor material has been applied successfully to the production of graded Al2O3/Al composites. For this purpose, distinct porosity gradients were introduced into carbon materials via anodic oxidation. The graded structure of the carbon preforms was replicated using two subsequent infiltration steps to yield fully dense Al2O3/Al functionally graded materials with an interpenetrating network microstructure and a continuous variation of metal content.
Homogeneous Precipitation of Hydrous Tin Oxide Powders at Room Temperature Using Enzymatically Induced Gluconic Acid as a Precipitant
Authors: Kato Shinichi , Unuma Hidero , Ota Toshitaka , Takahashi Minoru
Published: July 2010

Hydrous tin oxide powders were precipitated at room temperature via the neutralization of sodium stannate with gluconic acid. The gluconic acid was generated by the oxidation of glucose, with the assistance of a glucose oxidase/catalase system. The hydrous tin oxide, which had a large surface area, was obtained when a high concentration of enzymes was used as a solution. However, the apparent sizes of the precipitates were ∼0.3 μm, independent of the enzyme concentration. The precipitates were converted to tin oxide via calcination at temperatures >400°C.
Fabrication of Free‐Standing Titania‐Based Gas Sensors by the Oxidation of Metallic Titanium Foils
Authors: Gouma Pelagia I. , Mills Michael J. , Sandhage Ken H.
Published: July 2010

A simple method for fabricating TiO2‐based sensors of CO(g) is demonstrated: the oxidation of Ti‐bearing foils. Metallic foils (35 μm thick) were converted into free‐standing, porous rutile foils (60 μm thick) by exposure to O2(g) at 800°—965°C. The oxidized foils contained thin (0.5—1 μm thick), regularly spaced oxide layers oriented parallel to the external surface. The exposure of such porous foils to increasing concentrations of CO(g) resulted in a monotonic increase in the steady‐state electrical resistance. Rutile foils sensitive to 50 ppm changes in CO(g) content with response times of a few minutes were produced. The effects of oxidation conditions and copper doping on sensing performance are discussed.
Role of Carbon in the Sintering of Boron‐Doped Silicon Carbide
Authors: Clegg William J.
Published: July 2010

The effect of carbon on the sintering of boron‐doped SiC was studied. The free carbon present in the green compact was found to react with the SiO2 covering the surfaces of the SiC particles; however, even if no carbon was added, the surface SiO2 reacted with the SiC itself at a slightly higher temperature. This latter reaction was associated with the onset of substantial pore growth in the shrinking green body, which, as the pores continued to grow at higher temperatures, prevented complete densification. Therefore, the reaction of the SiC with the SiO2 may have led to the fracture of interparticle contacts, resulting in the onset of coarsening. Thus, the role of the carbon was to prevent reaction between the SiC and the surface SiO2, by removing the SiO2 at a temperature below that at which this reaction could occur.
Infiltration and Pyrolysis of Polytitanocarbosilane in an Si‐Ti‐C‐O Fabric/Mullite Porous Composite
Authors: Hirata Yoshihiro , Matsura Tsuyoshi , Hayata Kazunori
Published: July 2010

Incorporating Si‐Ti‐C‐O fabric into a mullite matrix is expected to increase the fracture energy of mullite ceramics. The present paper describes the processing of an Si‐Ti‐C‐O fabric/mullite/polytitanocarbosilane composite. A polytitanocarbosilane (a precursor of Si‐Ti‐C‐O fiber)/xylene solution was infiltrated into a laminated porous mullite composite with 35–37 vol% fabric and thermally decomposed to an amorphous solid at 1000°C, in an argon atmosphere, to decrease the porosity and residual stress induced by the difference in thermal and mechanical properties between the Si‐Ti‐C‐O fabric and the mullite. The decrease in porosity of the composite with pyrolysis of the precursor polymer was analyzed theoretically, and those results were used to control the effective experimental parameters. The infiltration/pyrolysis process was repeated eight times to produce a composite of 90.4% theoretical density. The composite exhibited significant pseudoductility, with a fracture energy of 11.4 kJ/m2 and a flexural strength of 290 MPa.
Synthesis of Aluminum Nitride–Silicon Carbide Solid Solutions by Combustion Nitridation
Authors: Ohyanagi Manshi , Shirai Kenshiro , Balandina Nadejda , Hisa Masaaki , Munir Zuhair A.
Published: July 2010

AlN–SiC solid solutions were synthesized via a combustion nitridation process. Reactions between powder mixtures of aluminum, silicon, and carbon or aluminum with β‐SiC and gaseous nitrogen under pressures of 0.1–8.0 MPa are self‐sustaining once they have been initiated. Investigations were made with reactant ratios of Al:Si:C = 7:3:3, 6:4:4, and 5:5:5 and Al:SiC = 7:3, 6:4, and 5:5. For the Al‐Si‐C system (molar ratio of 6:4:4), the maximum combustion temperature was dependent on the nitrogen pressure, increasing from 2300°C to 2480°C with an increase in pressure, from 0.1 MPa to 6.0 MPa. In all cases, the product contained the solid solution as the primary phase, with minor amounts of silicon. The amount of unreacted silicon decreased as the nitrogen pressure increased; the presence and dependence of unreacted silicon on pressure has been explained in terms of the volatilization of aluminum. The full width at half maximum for the (110) peak of the AlN–SiC solid solution decreased as the nitrogen pressure increased, which indicated the formation of a more homogeneous product.
Characterization of Fine‐Grained Bismuth Vanadate Ceramics Obtained Using Nanosized Powders
Authors: Shantha Kundapura , Varma Kalidindi B. R.
Published: July 2010

Nanocrystalline bismuth vanadate (n‐BiV) powders with a crystallite size of <50 nm have been prepared, at room temperature, by subjecting a stoichiometric mixture of bismuth oxide and vanadium pentoxide to mechanical activation. The n‐BiV powders show enhanced sinterability, in comparison to the conventionally prepared micrometer‐sized bismuth vanadate (m‐BiV) powders and yield ceramics with a uniform microstructure. High‐density (∼98% of the theoretical value), fine‐grained (average grain size of ∼2 μm) ceramics, obtained using n‐BiV have a high dielectric constant and a high pyroelectric coefficient and are associated with low dielectric loss, both at room temperature and at the transition temperature. These fine‐grained ceramics show diffused phase transition and relaxor behavior, which are attributed to the irregular distribution of defects and/or compositional inhomogeneities in these ceramics. The fine‐grained ceramics exhibit ferroelectric hysteresis loops with higher remanent polarization and lower coercive field values than the coarse‐grained ceramics.
Piezospectroscopic Analysis of Interface Debonding in Thermal Barrier Coatings
Authors: Peng Xiao , Clarke David R.
Published: July 2010

One of the principal modes by which electron‐beam‐evaporated thermal barrier coatings fail is via the nucleation of local regions of debonding, which grow and link together until reaching a critically sized flaw for spontaneous buckling and spalling. This progressive‐failure mode is used as a basis for analyzing the changes that can occur in photostimulated luminescence spectra that have been recorded from the thermally grown oxide. This process also provides a basis for the quantitative determination of the extent of local damage prior to spalling from an analysis of the shape of the luminescence spectra.
Effects of an Electric Field on the Fracture Toughness of Poled Lead Zirconate Titanate Ceramics
Authors: Fu Ran , Zhang Tong‐Yi
Published: July 2010

Compact tension tests and indentation‐fracture tests have been conducted to study the effects of an applied electric field on the fracture toughness (KIC) of poled commercial lead zirconate titanate (PZT) ceramics. The experimental results show that an applied electric field, either parallel or antiparallel to the poling direction, considerably reduces the KIC value of the PZT ceramics. The reduction in KIC for a negative field is larger than that for a positive field of the same strength. The failure mode in the PZT ceramics is basically transgranular, insensitive to the applied electric field.
Characterization of Photoluminescent (Y1–xEux)2O3 Thin Films Prepared by Metallorganic Chemical Vapor Deposition
Authors: McKittrick Joanna , Bacalski Carlos F. , Hirata G. A. , Hubbard Kevin M. , Pattillo S. G. , Salazar Kenneth V. , Trkula M.
Published: July 2010

The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium‐doped Y2O3 (Y1–xEux)2O3 thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y1–xEux)2O3 thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6‐tetramethyl–3,5‐heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 × 103 Pa)) and low substrate temperatures (500°–700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y2O3, grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y1–xEux)2O3 was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area‐reduction effect.
Al2O3–Ni Composites with High Strength and Fracture Toughness
Authors: Fahrenholtz William G. , Ellerby Donald T. , Loehman Ronald E.
Published: July 2010

Al2O3–Ni composites were prepared by the reactive hot pressing of Al and NiO. The composites had a two‐phase, interpenetrating microstructure and contained ∼35 vol% Ni. They exhibited an impressively high combination of strength and toughness at room temperature; the four‐point bending strength was in excess of 600 MPa with a fracture toughness of more than 12 MPa·m1/2. Examination of fracture surfaces showed that Ni ligaments underwent ductile deformation during fracture. SEM analysis revealed knife‐edged Ni ligaments with a limited amount of debonding around their periphery (i.e., at the Ni–Al2O3 interface), indicating a strong Ni–Al2O3 bond.
Preparation and Spherical Agglomeration of Crystalline Cerium(IV) Oxide Nanoparticles by Thermal Hydrolysis
Authors: Hirano Masanori , Fukuda Yuji , Iwata Hiroyuki , Hotta Yuji , Inagaki Michio
Published: July 2010

Crystalline cerium(IV) oxide nanoparticles with a cubic fluorite structure could be synthesized from cerium(IV) ammonium nitrate solutions with a relatively high concentration of cerium(IV) (such as 0.5 mol/dm3) via thermal hydrolysis at 150°–240°C. The effects of the treatment temperature, the salt concentration, and the addition of sulfate ions on the crystallite size and morphology of the synthesized particles were investigated. The crystalline nanoparticles had a tendency to agglomerate and form spherical secondary particles with the addition of either ammonium sulfate or sulfuric acid. The existence of sulfate ions in the acidified solution was confirmed to be a factor of consequence for spherical agglomeration of the nanoparticles.
Forming Al2O3–Al Composites with Controlled Compositions by Reactive Metal Penetration of Dense Aluminosilicate Preforms
Authors: Fahrenholtz William G. , Ellerby Donald T. , Ewsuk Kevin G. , Loehman Ronald E.
Published: July 2010

Alumina–Al composites with controlled compositions containing 17 to 31 vol% Al were formed by reactive metal penetration (RMP) of molten Al into dense aluminosilicate preforms. A reaction model has been developed to accurately predict composite Al content from the SiO2:Al2O3 ratio of the preform. The model was tested and validated by comparing predicted composite compositions to those measured for RMP composites made from preforms of known compositions. Aluminosilicate preforms containing 28.1, 39.0, and 54.1 wt% SiO2 were reacted with Al to produce composites with 17, 25, and 31 vol% Al, respectively. These values compare favorably to Al contents of 17.7, 22.7, and 28.6 vol% Al predicted using the reaction model. The differences between predicted and measured values are attributed to the presence of porosity and Si in the composites, as well as impurities in the SiO2 glass phase and porosity in the preforms, none of which is specifically accounted for in the reaction model.
X‐ray Studies of Ferroelectric Cathodes
Authors: Zhang Shuren , Cai Xumei , Zhong Chaowei , Zhu Wenyi
Published: July 2010

Ferroelectric electron emission has two possible sources: rapid polarization switching and surface plasma discharge. The present paper uses an X‐ray diffraction (XRD) method to support the theory of rapid polarization switching for lead zirconate titanate samples. A decrease in the 002 peak value and an increase in the 200 peak value were observed after electron emission in two types of samples, which were doped with lanthanum and neodymium. A comparison of the XRD data for the samples showed that a high‐density electron emission was related to a high‐value polarization switch. These results were consistent with the theory of rapid polarization switching.
In Situ Formation of Hexaferrite Magnets within a 3Y‐TZP Matrix: La2O3–ZnO–Fe2O3 and BaO–Fe2O3 Systems
Authors: Suzuki Yoshikazu , Calderón Héctor A. , Kondo Naoki , Ohji Tatsuki
Published: July 2010

The in situ formation of magnetoplumbite‐type (M‐type) hexaferrites within a 3Y‐TZP matrix was examined for the La2O3–ZnO–Fe2O3 and BaO–Fe2O3 systems. The formation of barium hexaferrite (Ba‐M) was rapid enough at a temperature of 1300°C for 2 h to result in a uniform dispersion of fine Ba‐M particles in a tetragonal zirconia polycrystal (TZP) matrix. However, the formation of lanthanum‐substituted hexaferrite (La‐M) was rather sluggish, despite the existence of a charge‐compensating divalent oxide. The 3Y‐TZP/20‐wt%‐BaFe12O19in situ composite possessed good magnetic properties, as well as moderately good mechanical properties.
Improvement in Time‐Dependent Displacement Degradation of Piezoelectric Ceramics by Manganese/Indium Addition
Authors: Sakai Takenobu , Kawamoto Hiroshi
Published: July 2010

High‐durability lead zirconate titanate (PZT) ceramics were developed in the present study to prevent time‐dependent deterioration of displacement, as well as failure under operation. Current leakage in PZT was decreased by adding elemental manganese, changing the zirconium content from 54.0 to 54.2 mol%, and decreasing the antimony content. Displacement was improved by adding both manganese and indium to the PZT. The present investigation resulted in the development of PZT compositions with high displacement and low time‐dependent displacement degradation. These results were confirmed by analyzing stack actuators made from enhanced PZT compositions.