Showing papers in "Journal of the American Ceramic Society in 2006"
TL;DR: In this paper, the main processing routes that can be used for the fabrication of macroporous ceramics with tailored microstructure and chemical composition are reviewed and compared in terms of microstructures and mechanical properties.
Abstract: Macroporous ceramics with pore sizes from 400 nm to 4 mm and porosity within the range 20%–97% have been produced for a number of well-established and emerging applications, such as molten metal filtration, catalysis, refractory insulation, and hot gas filtration. These applications take advantage of the unique properties achieved through the incorporation of macropores into solid ceramics. In this article, we review the main processing routes that can be used for the fabrication of macroporous ceramics with tailored microstructure and chemical composition. Emphasis is given to versatile and simple approaches that allow one to control the microstructural features that ultimately determine the properties of the macroporous material. Replica, sacrificial template, and direct foaming techniques are described and compared in terms of microstructures and mechanical properties that can be achieved. Finally, directions to future investigations on the processing of macroporous ceramics are proposed.
1,638 citations
TL;DR: In this paper, a clear picture has emerged of the principal factors, that influence microwave properties, and gives examples of where they have been used to control microwave properties and ultimately develop new materials.
Abstract: Temperature-stable, medium-permittivity dielectric ceramics have been used as resonators in filters for microwave (MW) communications for several decades. The growth of the mobile phone market in the 1990s led to extensive research and development in this area. The main driving forces were the greater utilization of available bandwidth, that necessitates extremely low dielectric loss (high-quality factor), an increase in permittivity so that smaller components could be fabricated, and, as ever in the commercial world, cost reduction. Over the last decade, a clear picture has emerged of the principal factors, that influence MW properties. This article reviews these basic principles and gives examples of where they have been used to control microwave properties and ultimately develop new materials.
948 citations
TL;DR: In this article, both droplet-and filament-based direct ink writing (DIW) techniques are presented, and various ink designs and their corresponding rheological behavior, ink deposition mechanics, potential shapes and the toolpaths required.
Abstract: The ability to pattern ceramic materials in three dimensions (3D) is critical for structural, functional, and biomedical applications. One facile approach is direct ink writing (DIW), in which 3D structures are built layer-by-layer through the deposition of colloidal- or polymer-based inks. This approach allows one to design and rapidly fabricate ceramic materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. In this feature article, we present both droplet- and filament-based DIW techniques. We focus on the various ink designs and their corresponding rheological behavior, ink deposition mechanics, potential shapes and the toolpaths required, and representative examples of 3D ceramic structures assembled by each technique. The opportunities and challenges associated with DIW are also highlighted.
637 citations
TL;DR: In this article, a brief overview of recent progress in preparation of ceramic nanofibers by electrospinning, with a focus on an introduction to experimental procedures and analysis of several technical issues that are vital for a successful electro-spinning experiment.
Abstract: Electrospinning is a remarkably simple method for generating nanofibers of polymers. When combined with conventional sol–gel processing, it provides a versatile technique for producing ceramic nanofibers with either a solid, porous, or hollow structure. This article presents a brief overview of recent progress in preparation of ceramic nanofibers by electrospinning, with a focus on an introduction to experimental procedures and analysis of several technical issues that are vital for a successful electrospinning experiment. We also highlight the unique capabilities of this technique in processing ceramic materials into nanostructures, and illustrate some potential applications of these nanostructures.
482 citations
TL;DR: In this article, the microwave characteristics of two dielectric resonator materials were investigated and the relationship between the micro-structures of these materials and dielectrics loss was determined.
Abstract: The microwave characteristics of two dielectric resonator materials were investigated. This research included (Zr, Sn)TiO4, a material having the characteristics of a dielectric constant K= 38, Q= 7000 at 7 GHz, and temperature coefficient of resonant frequency τf, = 0 ppm/°C. The investigation determined the relations between the dielectric loss and micro-structures of this ceramic. Analysis by X-ray microanalyzer made it clear that the addition of Fe2O3 increased the dielectric loss of this ceramic because the Fe ions diffused into the grain. The other material investigated was BaO-PbO-Nd2O3-TiO2, a ceramic having a dielectric constant of K= 88, Q= 5000 at 1 GHz, and τf= 0 ppm/°C. As this ceramic has a very high dielectric constant, it is useful for applications at frequencies <1 GHz.
464 citations
TL;DR: In this paper, the authors investigated the thermochemical aspects of the degradation phenomena using a model CMAS composition and ZrO2-7.6%YO1.5 (7YSZ) grown by vapor deposition on alumina substrates.
Abstract: Thermal barrier coatings (TBCs) are increasingly susceptible to degradation by molten calcium–magnesium alumino silicate (CMAS) deposits in advanced engines that operate at higher temperatures and in environments laden with siliceous debris. This paper investigates the thermochemical aspects of the degradation phenomena using a model CMAS composition and ZrO2–7.6%YO1.5 (7YSZ) grown by vapor deposition on alumina substrates. The changes in microstructure and chemistry are characterized after isothermal treatments of 4 h at 1200°–1400°C. It is found that CMAS rapidly penetrates the open structure of the coating as soon as melting occurs, whereupon the original 7YSZ dissolves in the CMAS and reprecipitates with a different morphology and composition that depends on the local melt chemistry. The attack is minimal in the bulk of the coating but severe near the surface and the interface with the substrate, which is also partially dissolved by the melt. The phase evolution is discussed in terms of available thermodynamic information.
457 citations
TL;DR: In this paper, a novel method for depositing ceramic thick films by aerosol deposition (AD) is presented, where submicron ceramics particles are accelerated by gas flow up to 100-500 m/s and then impacted on a substrate, to form a dense, uniform and hard ceramic layer at room temperature.
Abstract: A novel method for depositing ceramic thick films by aerosol deposition (AD) is presented. Submicron ceramics particles are accelerated by gas flow up to 100–500 m/s and then impacted on a substrate, to form a dense, uniform and hard ceramic layer at room temperature. However, actual deposition mechanism has not been clarified yet. To clarify densification mechanism during AD, a mixed aerosol of α-Al2O3 and Pb(Zr, Ti)O3 powder was deposited to form a composite layer in this study. The cross-section of the layer was observed by HR-TEM to investigate the densification and bonding mechanism of ceramic particles. As a result, a plastic deformation of starting ceramic particles at room temperature was observed.
448 citations
TL;DR: In this paper, highly dense Niobate ceramics were prepared using spark plasma sintering (SPS). Although the SPS temperature was as low as 920 C, the density of the Na 0.5 K 0.5 NbO 3 solid solution was raised to 4.47 g/cm 3 (>99% of the theoretical density).
Abstract: Lead-free piezoelectric ceramics have received attention because of increasing interest in environmental protection. Niobate ceramics such as NaNbO 3 and KNbO 3 have been studied as promising Pb-free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, highly dense Na 0.5 K 0.5 NbO 3 ceramics were prepared using spark plasma sintering (SPS). Although the SPS temperature was as low as 920 C, the density of the Na 0.5 K 0.5 NbO 3 solid solution ceramics was raised to 4.47 g/cm 3 (>99% of the theoretical density). After post-annealing in air, reasonably good ferroelectric and piezoelectric properties were obtained in the Na 0.5 K 0.5 NbO 3 ceramics with submicron grains. The crystal phase of the Na 0.5 K 0.5 NbO 3 has an orthorhombic structure. The Curie temperature is 395°C and the piezoelectric parameter (d 33 ) of the Na 0.5 K 0.5 NbO 3 ceramics reached 148 pC/N.
422 citations
TL;DR: In this article, a mechanics model of micro-crack toughening is presented, which predicts the magnitude of microcracks as well as the existence of R-curve effects.
Abstract: A mechanics model of microcrack toughening is presented. The model predicts the magnitude of microcrack toughening as well as the existence of R-curve effects. The toughening is predicated on both the elastic modulus diminution in the microcrack process zone and the dilatation induced by microcracking. The modulus effect is relatively small and process-zone-size-independent. The dilatational effect is potentially more substantial, as well as being the primary source of the R curve. The dilatational contribution is also zone-size-dependent. The analysis demonstrates that microcrack toughening is less potent than transformation toughening.
421 citations
TL;DR: In this paper, the experimental and theoretical basis of ceramic e-spinning is reviewed and an expanded electro hydrodynamic (EHD) theory is proposed to predict fired fiber diameter for lanthanum cuprate fibers.
Abstract: During the last years, several groups across the world have concentrated on the adaptation and further development of electrospinning (e-spinning) to enable ceramic fiber synthesis. Thus far, more than 20 ceramic systems have been synthesized as micro- and nanofibers. These fibers can be amorphous, polycrystalline, dense, porous, or hollow. This article reviews the experimental and theoretical basis of ceramic e-spinning. Furthermore, it introduces an expanded electro hydrodynamic (EHD) theory that allows the prediction of fired fiber diameter for lanthanum cuprate fibers. It is hypothesized that this expanded EHD theory is applicable to most ceramic e-spinning systems. Furthermore, electroceramic nanofibers produced via e-spinning are presented in detail along with an overview of electrospun ceramic fibers.
409 citations
TL;DR: In this article, the Adam-Gibbs equation is shown to describe accurately both τ and the viscosity of NBS 710 (alkali lime silicate) glass.
Abstract: Narayanaswamy's model of structural relaxation has been shown to provide an excellent description of the behavior of a variety of glasses. In the standard formulation, the relaxation time, τ is represented by the Arrhenius equation, with the activation energy partitioned between the temperature and Active temperature. That form for τ is successful, but lacks theoretical justification. In this paper, the Adam-Gibbs equation is shown to describe accurately both τ and the viscosity of NBS 710 (alkali lime silicate) glass. This equation is expected to be accurate over a wider range of temperature and Active temperature than the Arrhenius equation.
TL;DR: In this paper, a relatively large remanent polarization was produced, ranging from 16 μC/cm2 for pure Na0.5K 0.5NbO3 (NKN) piezoelectric ceramics to 23 µC/ cm2 for ZnO-added NKN samples.
Abstract: Lead-free Na0.5K0.5NbO3 (NKN) piezoelectric ceramics were fairly well densified at a relatively low temperature under atmospheric conditions. A relative density of 96%–99% can be achieved by either using high-energy attrition milling or adding 1 mol% oxide additives. It is suggested that ultra-fine starting powders by active milling or oxygen vacancies and even liquid phases from B-site oxide additives mainly lead to improved sintering. Not only were dielectric properties influenced by oxide additives, such as the Curie temperature (Tc) and dielectric loss (D), but also the ferroelectricity was modified. A relatively large remanent polarization was produced, ranging from 16 μC/cm2 for pure NKN to 23 μC/cm2 for ZnO-added NKN samples. The following dielectric and piezoelectric properties were obtained: relative permittivity ɛT33/ɛ0=570–650, planar mode electromechanical coupling factor, kp=32%–44%, and piezoelectric strain constant, d33=92–117 pC/N.
TL;DR: In this article, the effects of the pulsed direct current on the neck formation and the neck growth of conducting powders were investigated, and it was found that there is a considerable inhomogeneous distribution of the temperature increase from the particle-contacting surface to the center of the particle when the pulsing current passes through.
Abstract: By using spherical Cu powders as the conducting sintering material, the microstructures of sintered powder particles at different stages in the process of spark plasma sintering (SPS) have been investigated. Theoretical analyses are proposed to quantify the effects of the pulsed direct current on the neck formation and the neck growth of conducting powders. It is found that there is a considerable inhomogeneous distribution of the temperature increase from the particle-contacting surface to the center of the particle when the pulsed current passes through. The temperature at the particle-contacting surface may reach the boiling point of the material, which results in neck formation at relatively low-sintering temperatures through a process of local melting and rapid solidification. The neck growth depends on the local distribution of the current intensity, which is determined by the competition between the neck cross-sectional area and the electrical resistivity increasing with the temperature. Accordingly, we propose that the coarsening of necks follows a "self-adjusting" mechanism, which is likely to be the essential reason for the homogeneous distributions of neck sizes and sizes of fine grains formed in the neck zones during the SPS process.
TL;DR: In this paper, isothermal and constant-grain-size sintering was carried out to full density in Y2O3 with and without dopants, at as low as 40% of the homologous temperature.
Abstract: Isothermal and constant-grain-size sintering have been carried out to full density in Y2O3 with and without dopants, at as low as 40% of the homologous temperature. The normalized densification rate follows Herring's scaling law with a universal geometric factor that depends only on density. The frozen grain structure, however, prevents pore relocation commonly assumed in the conventional sintering models, which fail to describe our data. Suppression of grain growth but not densification is consistent with a grain boundary network pinned by triple-point junctions, which have a higher activation energy for migration than grain boundaries. Long transients in sintering and grain growth have provided further evidence of relaxation and threshold processes at the grain boundary/triple point.
TL;DR: In this paper, the temperature of the cubic-hexagonal transition in barium metatitanate was determined as 1460°C. and the transition has been shown to be reversible.
Abstract: The system BaO-TiO2 was investigated using quenching, strip-furnace, and thermal techniques. Five compounds were found to exist in the system: Ba2TiO4, BaTiO3, BaTi2O5, BaTi3O7, and BaTi4O9. Of these, only barium metatitanate (BaTiO3) melts congruently (at 1618°C.). The dititanate melts incongruently at 1322° C. to yield BaTiO3 and liquid; the trititanate melts at 1357°C. to yield BaTi4O9 and liquid; the tetra-titanate melts to TiO2 and liquid at 1428° C. The nature of melting of the orthotitanate could not be determined accurately because of the high temperature involved and the rapid reaction with platinum. The two eutectics in the system occur between Ba2TiO4 and BaTiO3 at 1563°C. and between BaTi2O5 and BaTi3O7 at 1317°C. The temperature of the cubic-hexagonal transition in barium metatitanate was determined as 1460°C. and the transition has been shown to be reversible. The transition temperature is raised sharply by the addition of a small percentage of TiO2 although the extent of solid solution is quite limited. Some applications to the manufacture of titanate bodies and to the growth of single crystals of barium metatitanate are discussed.
TL;DR: In this article, the authors showed that Zirconium diboride (ZrB 2 ) was densified (>98% relative density) at temperatures as low as 1850°C by pressureless sintering.
Abstract: Zirconium diboride (ZrB 2 ) was densified (>98% relative density) at temperatures as low as 1850°C by pressureless sintering. Sintering was activated by removing oxide impurities (B 2 O 3 and ZrO 2 ) from particle surfaces. Boron oxide had a high vapor pressure and was removed during heating under a mild vacuum (∼150 mTorr). Zirconia was more persistent and had to be removed by chemical reaction. Both WC and B 4 C were evaluated as additives to facilitate the removal of ZrO 2 Reactions were proposed based on thermodynamic analysis and then confirmed by X-ray diffraction analysis of reacted powder mixtures. After the preliminary powder studies, densification was studied using either as-received ZrB 2 (surface area ∼ 1 m 2 /g) or attrition-milled ZrB 2 (surface area ∼ 7.5 m 2 /g) with WC and/or B 4 C as a sintering aid. ZrB 2 containing only WC could be sintered to ∼95% relative density in 4 h at 2050°C under vacuum. In contrast, the addition of B 4 C allowed for sintering to >98% relative density in 1 h at 1850°C under vacuum.
TL;DR: In this paper, the authors investigated the preparation of bulk dense nanocrystalline BaTiO 3 and Ni-Cu-Zn ferrite ceramics using an unconventional two-step sintering strategy, which offers the advantage of not having grain growth while increasing density from about 75% to above 96%.
Abstract: We investigated the preparation of bulk dense nanocrystalline BaTiO 3 and Ni-Cu-Zn ferrite ceramics using an unconventional two-step sintering strategy, which offers the advantage of not having grain growth while increasing density from about 75% to above 96%. Using nanosized powders, dense ferrite ceramics with a grain size of 200 nm and BaTiO 3 with a grain size of 35 nm were obtained by two-step sintering. Like the previous studies on Y 2 O 3 , the different kinetics between densification diffusion and grain boundary network mobility leaves a kinetic window that can be utilized in the second-step sintering. Evidence indicates that low symmetry, ferroelectric structures still exist in nanograin BaTiO 3 ceramics, and that saturation magnetization is the same in nanograin and coarse grain ferrite ceramics.
TL;DR: The dielectric properties and chemical homogeneity of BaTiO3 ceramics sintered with additions of the pseudophase "CdBi2Nb2O9" were investigated using SEM, TEM, STEM, and EDX as mentioned in this paper.
Abstract: The dielectric properties and chemical homogeneity of BaTiO3 ceramics sintered with additions of the pseudophase “CdBi2Nb2O9” were investigated using SEM, TEM, STEM, and EDX. In materials showing the “X7R” dielectric temperature characteristic, the microstructure exhibits the grain core-grain shell structure. The perovskite material in the shell shows a temperature characteristic determined by mixed crystals of BaTiO3 with the complex perovskites Ba(Bi1/2Nb1/2)O3 and Ba(Cd1/3Nb2/3)O3 having an approximate Curie point of -80°C. The chemical inhomogeneity emerges during a process of reactive liquid-phase sintering. Application of too-high sintering temperatures leads to uniform distributions of the additives via solid-state diffusion and to the loss of the X7R characteristic.
TL;DR: In this article, Zirconium diboride (ZrB 2 ) ceramics were sintered to a relative density of ∼ 98% without applied external pressure.
Abstract: Zirconium diboride (ZrB 2 ) ceramics were sintered to a relative density of ∼ 98% without applied external pressure. Densification studies were performed in the temperature range of 1900 -2150 C. Examination of bulk density as a function of temperature revealed that shrinkage started at ∼2100°C, with significant densification occurring at only 2150°C. At 2150°C, isothermal holds were used to determine the effect of time on relative density and microstructure. For a hold time of 540 min at 2150 C, ZrB 2 pellets reached an average density of 6.02±0.04 g/cm 3 (98% of theoretical) with an average grain size of 9.0 ±5.6 μm. Four-point bend strength, elastic modulus, and Vickers' hardness were measured for sintered ZrB 2 and compared with values reported for hot-pressed materials. Vickers' hardness of sintered ZrB 2 was 14.5±2.6 GPa, which was significantly lower when compared with 23 GPa for hot-pressed ZrB 2 . Strength and elastic modulus of the ZrB 2 were 444±30 MPa and 454 GPa, which were comparable with values reported for hot-pressed ZrB 2 . The ability to densify ZrB 2 ceramics without hot pressing should enable near-net shape processing, which would significantly reduce the cost of fabricating ZrB 2 components compared with conventional hot pressing and machining.
TL;DR: In this paper, a model for the yield stress of particulate suspensions is presented that incorporates microstructural parameters taking into account volume fraction of solids, particle size and particle size distribution, maximum packing, percolation threshold, and interparticle forces.
Abstract: A model for the yield stress of particulate suspensions is presented that incorporates microstructural parameters taking into account volume fraction of solids, particle size, particle size distribution, maximum packing, percolation threshold, and interparticle forces. The model relates the interparticle forces between particles of dissimilar size and the statistical distribution of particle pairs expected for measured or log-normal size distributions. The model is tested on published data of sub-micron ceramic suspensions and represents the measured data very well, over a wide range of volume fractions of solids. The model shows the variation of the yield stress of particulate suspensions to be inversely proportional to the particle diameter. Not all the parameters in the model could be directly evaluated; thus, two were used as adjustable variables: the maximum packing fraction and the minimum interparticle separation distance. The values for these two adjustable variables provided by the model are in good agreement with separate determinations of these parameters. This indicates that the model and the approximations used in its derivation capture the main parameters that influence the yield stress of particulate suspensions and should help us to better predict changes in the rheological properties of complex suspensions. The model predicts the variation of the yield stress of particulate suspensions to be inversely proportional to the particle diameter, but the experimental results do not show a clear dependence on diameter. This result is consistent with previous evaluations, which have shown significant variations in this dependence, and the reasons behind the yield stress dependence on particle size are discussed in the context of the radius of curvature of particles at contact.
TL;DR: In this paper, the authors present a model for these nanodomains, which is consistent with the nuclear magnetic resonance (NMR) data and with the phenomenological properties of SiCO (high resistance to creep and viscoelastic behavior).
Abstract: The polymer-based synthesis of ceramics such as SiCO (and SiCN) leads to the incorporation of significant amounts of carbon into their molecular structure. A key feature of the nanostructure of these polymer-derived ceramics is the revelation of persistent, 1-5 nm size domains by small-angle X-ray scattering. Here we present a model for these nanodomains, which is consistent with the nuclear magnetic resonance (NMR) data and with the phenomenological properties of SiCO (high resistance to creep and viscoelastic behavior). The model consists of clusters of silica tetrahedra encased within an interdomain wall constituted from mixed bonds of SiCO, and from a network of sp 2 carbon. The model predicts the domain size as a function of the carbon content. These predictions are in reasonable agreement with the measurements of the nanodomains in SiCO synthesized with varying carbon contents (the domain size decreases with higher carbon). Simple maps are developed for easy reading of the domain size and the width of the interdomain boundary in the composition diagrams.
TL;DR: In this article, the optimal sintering condition for densification, microstructure, and electrical properties of Li-doped and Li/Ta-codoped potassium sodium niobate (KNbO 3)-based ceramics was investigated.
Abstract: Normal sintering of Li-doped and Li/Ta-codoped potassium sodium niobate (KNbO 3 -NaNbO 3 , KNN)-based ceramics was investigated to clarify the optimal sintering condition for densification, microstructure, and electrical properties. It was found that density increased greatly within a narrow temperature range but tended to decrease when the sintering temperature slightly exceeded the optimal one, accompanied by the appearance of abnormal grain growth, which was considered to be due to the intensified volatilization of alkali metal oxides. Piezoelectric and dielectric properties also showed a similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density, because both densification and composition affect the electrical properties. The highest d 33 value of 206 pC/N was obtained for the Li-and Ta-codoped KNN ceramics prepared at 1090°C.
TL;DR: In this article, a colloidal mixture of Al2O3/ZrO2 composite powders was mixed and consolidated by a colloid method, sintered to >98% theoretical density at 1550°C, and subsequently heat-treated at temperatures up to 1700°C for grain-size measurements.
Abstract: Alumina and Al2O3/ZrO2 (1 to 10 vol%) composite powders were mixed and consolidated by a colloidal method, sintered to >98% theoretical density at 1550°C, and subsequently heat-treated at temperatures up to 1700°C for grain-size measurements. Within the temperature range studied, the ZrO2 inclusions exhibited sufficient self-diffusion to move with the Al2O3 4-grain junctions during grain growth. Growth of the ZrO2, inclusions occurred by coalescence. The inclusions exerted a dragging force at the 4-grain junctions to limit grain growth. Abnormal grain growth occurred when the inclusion distribution was not sufficiently uniform to hinder the growth of all Al2O3 grains. This condition was observed for compositions containing ≤2.5 vol% ZrO2, where the inclusions did not fill all 4-grain junctions. Exaggerated grains consumed both neighboring grains and ZrO2, inclusions. Grain-growth control (no abnormal grain growth) was achieved when a majority (or all) 4-grain junctions contained a ZrO2 inclusion, viz., for compositions containing ≥5 vol% ZrO2. For this condition, the grain size was inversely proportional to the volume fraction of the inclusions. Since the ZrO2 inclusions mimic voids in all ways except that they do not disappear, it is hypothesized that abnormal grain growth in single-phase materials is a result of a nonuniform distribution of voids during the last stage of sintering.
TL;DR: In this paper, the electrical properties of a series of CaCu3Ti4O12 ceramics prepared by the mixed oxide route and sintered at 1115°C in air for 1-24 h to produce different ceramic microstructures have been studied by Impedance Spectroscopy.
Abstract: The electrical properties of a series of CaCu3Ti4O12 ceramics prepared by the mixed oxide route and sintered at 1115°C in air for 1–24 h to produce different ceramic microstructures have been studied by Impedance Spectroscopy. As-fired ceramics are electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries, and can be modelled to a first approximation on an equivalent circuit based on two parallel RC elements connected in series. The grain boundary resistance and capacitance values vary as a function of sintering time and correlate with the ceramic microstructure based on the brickwork layer model for electroceramics. The large range of apparent high permittivity values for CaCu3Ti4O12 ceramics is therefore attributed to variations in ceramic microstructure. The grain-boundary resistance decreases by three to four orders of magnitude after heat treatment in N2 at 800°–1000°C but can be recovered to the original value by heat treatment in O2 at 1000°C. The bulk resistivity decreases from ∼80 to 30 Ω·cm with increasing sintering time but is independent of heat treatment in N2 or O2 at 800°–1000°C. The origin of the bulk semiconductivity is discussed and appears to be related to partial decomposition of CaCu3Ti4O12 at the high sintering temperatures required to form dense ceramics, and not to oxygen loss.
TL;DR: In this article, lead-free piezoelectric NaxK1−xNbO3 (x=20−80 mol%) ceramics were fabricated using spark plasma sintering at a low temperature (920°C).
Abstract: Lead-free piezoelectric NaxK1−xNbO3 (x=20–80 mol%) ceramics were fabricated using spark plasma sintering at a low temperature (920°C). All the NaxK1−xNbO3 ceramics showed a similar orthorhombic phase structure, while the corresponding lattice parameters decreased from the KNbO3 side to the NaNbO3 side with increasing Na content. A discontinuous change in lattice parameter close to composition of 60 mol% Na indicated the presence of a transitional area that is similar to the morphotropic phase boundary (MPB) in NaxK1−xNbO3 ceramics. The sintered density of the NaxK1−xNbO3 ceramics decreased with increasing Na content, from a relative density of 99% for the K-rich side to 92% for the Na-rich side. The piezoelectric constant d33 and planar mode electromechanical coupling coefficient kp showed a maximum value of 148 pC/N and 38.9%, respectively, due to the similar MPB effects in the PZT system.
TL;DR: In this paper, two series of xerogels (desiccated hydrogels), one consisting of single phases and the other of two phases, were prepared from organic and inorganic precursors in the system Al2o3-Sio2.
Abstract: Two series of xerogels (desiccated hydrogels), one consisting of single phases and the other of two phases, were prepared from organic and inorganic precursors in the system Al2o3-Sio2. The effect of these nanostructural differences in the xerogel powders on the energy content and behavior on heating were studied using DTA, powder X-ray diffraction, and ultrafast heating on a strip furnace. The results demonstrate that diphasic xerogels are substantially different materials from single-phase xerogels of the same composition.
TL;DR: In this paper, a perovskite pseudocell and hexagonal superstructure were constructed for the dielectric resonator of the Ba(Ni,Ta)O3-BaZrO3 system.
Abstract: Microwave characteristics of the system Ba(Zn1/3Ta2/3)O3-BaZrO3 were investigated. Ba(Zn,Ta)O3 has a perovskite pseudocell and hexagonal superstructure; the superstructure was not formed after addition of BaZrO3. Both sintering and crystallization of Ba(Zn,Ta)O3-BaZrO3 were accelerated compared to those of Ba(Zn,Ta)O3 alone, and the microwave Q value was also improved. The material optimized for the dielectric resonator, Ba(Ni,Ta)O3-Ba(Zr,Zn,Ta)O3, has a dielectric constant of 30, Q value of 10000 at 10 GHz, and temperature coeficient of resonant frequency of 0 ppm/°C.
TL;DR: In this paper, the authors show that donor additions to BaTiO3 up to a few tenths atom percent are compensated by electrons and the resulting electrical conductivity is independent of temperature and Po2 at 700° to 1000°C.
Abstract: Donor additions to BaTiO3 up to a few tenths atom percent are compensated by electrons and the resulting electrical conductivity is independent of temperature and Po2 at 700° to 1000°C. The conductivities are impurity-insensitive at very low Poz and high temperature where reduction is the major source of defects. Variation in the site occupation ratio (A/B in ABO3 has a small effect on the conductivities for donor additions in the 100 ppm range. Nb is more effective as a donor than is Al as an acceptor, and Nb can compensate approximately 2½ times as much Al on an atomic basis.
TL;DR: In this article, the laser conversion efficiency of pore-free polycrystalline Nd:YAG (Y 3 Al 5 O 12 ) and Yb-doped YAG single crystal was reported.
Abstract: This paper reports recent progress in the production of polycrystalline Nd:YAG (Y 3 Al 5 O 12 ), Nd:YSAG (Y 3 Sc 1.0 Al 4.0 O 12 ), Yb:YSAG ceramics, and a Nd-doped YAG single crystal with an almost perfect pore-free structure by advanced ceramic processing. The laser conversion efficiency of pore-free polycrystalline Nd- and Yb-doped ceramics is extremely high, and their optical qualities are comparable with that of commercial high-quality Nd:YAG single crystals. We have also succeeded in the fabrication of a Nd:YAG single crystal, which can be used for laser oscillation, by the solid-state reaction method. Laser oscillation efficiency was very low when the pores remained inside the single crystal; however, the laser oscillation efficiency of the pore-free Nd:YAG single crystal was slightly higher than that of polycrystalline Nd:YAG ceramics having high optical quality. From this fact, it was recognized that optical scattering occurs mainly in the residual pores inside the Nd:YAG ceramics and the scattering at the grain boundary is very less. In addition, we confirmed that a heavily doped Nd:YAG single crystal can be fabricated by the sintering method. Moreover, we have demonstrated the fabrication of a composite ceramic with complicated structures without the need for precise polishing and diffusion bonding. Advanced ceramic processing, which enables design flexibility of the laser element, presented in this work is important in the development of a high-performance laser (high efficiency, high beam quality, and high output energy, etc.).
TL;DR: In this article, the influence of dopants on tricalcium phosphate (TCP) resorbable ceramics with special emphasis toward in vitro strength degradation and cell-materials interactions as a function of time was analyzed.
Abstract: Resorbable calcium phosphate (CaP)-based biomaterials are important because they can significantly improve health care by shortening the time necessary for restoration of functional loading of grafted bones. Although synthetic CaPs show exceptional similarities to natural bone, however, they are deficient in one major area, in that they do not have the same mineral content of bone. The focus of our work is to understand the influence of dopants on the physical, mechanical, and biological properties of tricalcium phosphate (TCP) resorbable ceramics with special emphasis toward in vitro strength degradation and cell–materials interactions as a function of time. For this purpose, β-TCP was doped with magnesia (MgO), zinc oxide (ZnO), and silica (SiO2). Those dopants were added as individual dopants, and their binary and ternary compositions. It was found that these dopants significantly influenced densification behavior and as sintered microstructures of TCP. In vitro mineralization studies in simulated body fluids (SBF) for 12 weeks showed apatite growth on the highly porous compositions either on the surface or inside. From scanning electron microscopic analysis it was evident that surface degradation occurred on all compositions in SBF. Compression strengths for samples up to 12 weeks in SBF showed that it is possible to tailor strength loss behavior through compositional modifications. The highest compression strength was found for binary MgO–ZnO doped TCP. Overall, samples showed either a similar strength level during the 12 weeks test period, or a continuous decrease or a continuous increase in strength depending on dopant chemistry or amount. In vitro human osteoblast cell culture was used to determine influence of dopants on cell-materials interactions. All samples were non-toxic and biocompatible. Dopant chemistry also influenced adhesion, proliferation, and differentiation of osteoblastic precursor cell line 1 (OPC1) cells on these matrices.