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Millimeter-wave wireless communications in a high-level information society have been expanding in terms of high-density data transfer and radar for pre-crash safety systems. α-wollastonite (CaSiO 3 ) based and SrSiO 3 based solid solutions (s.s.) in the CaSiO 3 -SrSiO 3 eutectic binary system are expected as millimeter-wave dielectrics because of low dielectric constant as described in a previous paper. In this paper, crystal structures of SrSiO 3 and Ca 0.2 Sr 0.8 SiO 3 compounds are analyzed by Rietveld method using X-ray powder diffraction (XRPD) patterns obtained at the PF-KEK, Tsukuba, Japan. Covalencies of Si O bonds are calculated through the bond strength obtained by the bond length, which at x = 0.8 were higher than that of at x = 1 as (Ca 1- x Sr x )SiO 3 . The lowest dielectric constant ( ε r ) and highest Qf value at x = 0.8 with ε r = 6.62, Qf = 66,700 GHz and τ f = –40 ppm/°C were explained by the covalencies. [ABSTRACT FROM AUTHOR]

Abstract At present, no suitable and convenient model has been developed to predict variation tendencies of fracture strength of laminated ceramic composites with temperature. In this paper, a novel and quite simple temperature dependent fracture strength model for the laminated ultra-high temperature ceramic composites was developed based on energy theories–the Griffith energy criterion and a concept of energy storage capacity. The complicated problems of characterization of combined effects of temperature, change in critical flaw size and laminated structure parameters on fracture strength are solved by using primary and simple method. The model prediction agreed well with the experimental value. The novel model can be used to determine both fracture strength and change in critical flaw size of laminated composite at elevated temperature. It should be noted that the model has no any fitting parameter, which is an easy-to-use method for the engineering. Highlights • A new model for predicting temperature dependent fracture strength is proposed. • Effects of critical flaw size and laminated structure are included in the model. • The model has no any fitting parameter and is quite simple. • Excellent agreement is achieved between model prediction and experimental data. [ABSTRACT FROM AUTHOR]

Recently a paper [Mater. Res. Bull. 35 (2000) 1153] has been published in which well known aspects of thermodynamic investigations on Na–beta-alumina were disregarded. These aspects are discussed below in the light of the current knowledge about the subject. As a consequence, the conclusions drawn in the cited paper that Na–β″-Al2O3 is not a stable phase must be considered as not justified. [Copyright &y& Elsevier]

In the process of predicting materials properties, it is necessary to predict microstructures. This is important for ceramic materials, for the purpose of miniaturization and for a higher level of integration. Although the method of material structure reconstruction is for the first time used on BaTiO 3 -ceramics by these authors, it can also be used for silicate, refractory and other ceramics, and, for any powder-based material. The reconstruction is based on the grain perimeter fractal analysis and the Richardson method. The main contribution of this paper is establishing the relationship between the electronic properties of BaTiO 3 -ceramics and its microstructural fractal nature. Similar relations can be used for any ceramics or even any materials. The samples consolidation includes both powder pressing (cold sintering phase) and sintering in a furnace (hot sintering phase). The fractal nature characterization has a very important role from the powder phase up to the final microstructure, through which structures it directly impacts electro-physical and other ceramics properties. Thereby, the new possibilities in the microstructure characterization applications are directly introduced to an engineering system, providing the new solutions related to computer aided support. This creates new industrial production and application possibilities, especially in the process of ceramics material consolidation, now based on microstructural properties, which is providing a basis for “fractal electronics’’ development. [ABSTRACT FROM AUTHOR]

This paper reports the observation of hexagonal phase of barium titanate by Mn doping and its effect on dielectric and magnetic properties. Ceramic samples of Ba 0.98 Zn 0.02 Ti 1− x Mn x O 3 (where, x = 0.04, 0.06 and 0.08) were prepared by traditional solid-state reaction route. The hexagonal phase is stabilized in the composition Ba 0.98 Zn 0.02 Ti 0.92 Mn 0.08 O 3 and a very feeble M – H loop is also observed in that composition. This induced magnetism is expected due to the exchange interactions between magnetic polarons formed by oxygen vacancies with Mn ions. The dielectric constant as well as the ferroelectric to paraelectric transition temperature is systematically decreased with increasing of Mn doping concentration. Further to that, the temperature dependent dielectric constant curve is also broadened at transition temperature with increasing of Mn concentration. However, the ferroelectric to paraelectric transition temperature is well above room temperature. [ABSTRACT FROM AUTHOR]

Miniaturization of patch antenna using composite ferrite (Ni 0.5 Zn 0.3 Co 0.2 Fe 2 O 4 + BaFe 12 O 19 ) is proposed in this paper. Substrate material was prepared using a wet chemical method and characterized for its structural and electromagnetic properties. Matching values of complex permittivity ( ε * = 4.5 + 0.1 j) and complex permeability ( μ * = 4.6 + 0.3 j) at 500 MHz were obtained from the electromagnetic characterization. Simulation result showed that matching and greater than unity value of both permittivity and permeability can reduce the size of antenna by almost 55%. Normalized characteristic impedance close to unity (∼1.022) was observed in the synthesized nano ferrite composites. This results in better impedance matching of the substrate with the surrounding space. Reflection loss was found to decrease (from −28 dB to −35 dB) and bandwidth increases (1.6–6%) over pure dielectric substrate. Therefore, composite ferrite is proposed as suitable candidate for effective miniaturization of antenna in microwave frequency range. [ABSTRACT FROM AUTHOR]

In this paper, we examine the power generation performance of a rotational electret power generator theoretically and experimentally using electrostatic induction based on the properties of hydroxyapatite (HAp) ceramic electrets; the two surfaces of the electrets have opposing polarities. The HAp electrets have long-term stability in comparison with polymer electrets, which are more commonly used. The theoretical power output is proportional to the square of the total surface area of electrets per block of the stator, frequency of the rotor, and surface electric potential of the electret. Moreover, the power output is proportional to the square of the inverse of the air gap between the rotor and electrets. The behavior of power outputs obtained under different experimental conditions correlated with our theoretical prediction. The maximum output power generated by our prototype electret generator was 3.6 μW with the frequency of the rotor being 24 Hz. [ABSTRACT FROM AUTHOR]

This paper studies calcium titanate (CaTiO 3 ) dielectrics prepared by plasma spray technology. A water stabilized plasma gun (WSP) as well as a widely used gas stabilized plasma gun (GSP) were employed in this study to deposit three sample sets at different spray conditions. Prepared specimens were annealed in air at atmospheric pressure for 2 h at various temperatures from 530 to 1170 °C. X-ray diffraction (XRD), Raman spectroscopy and porosity measurements were used for sample characterization. Dielectric spectroscopy was applied to obtain relative permittivity, conductivity and loss factor frequency dependence. Band gap energy was estimated from reflectance measurements. The work is focused on the explanation of changes in microstructure and properties of a plasma sprayed deposit after thermal annealing. Obtained results show significant improvement of dielectric properties after thermal annealing. [ABSTRACT FROM AUTHOR]

This paper studied the preparation and characterization of LTCC (low temperature co-fired ceramics) materials based on BaO–B 2 O 3 –SiO 2 /BaTiO 3 glass–ceramics, where the sintering temperature was about 900 °C and dielectric constant was effectively adjustable from 5 to 30 by changing the BaTiO 3 fraction from 60 wt% to 90 wt%. X-ray diffractometer (XRD), scanning electron microscopy (SEM) were used to examine the effect of different amounts additive on the dielectric properties of this LTCC system and the crystal structure change. The results indicated that BaTiO 3 can be used as a dielectric additive aim to adjust the permittivity of BaO–B 2 O 3 –SiO 2 glass, which the main influence factors on dielectric are the contents of the secondary phase, the BaTiO 3 phase fraction and the porous structure of the sintered body. Therefore, the microstructure and dielectric property of BaO–B 2 O 3 –SiO 2 /BaTiO 3 glass–ceramics composites could be controlled by adjusting the content of BaTiO 3 additive. [ABSTRACT FROM AUTHOR]

The present paper reports on the successful fabrication of micro-sized pillar arrays of Ba 0.6 Sr 0.4 TiO 3 (BST) electroceramics via cost effective epoxy gel casting (EGC) consolidation method based on the in situ polymerization of aqueous suspensions with added water soluble epoxy resin. The synthesized BST solid solution powder was fine milled and surface protected against hydrolysis to avoid its degradation in the aqueous environment. The micro patterning process was divided in the following steps: (i) production of high quality SU-8 master moulds by photolithography and of the respective negative replicas in PDMS (soft mould); (ii) casting of stable high solid loading BST suspensions in the soft moulds with added setting agents followed by de-moulding, drying and sintering. Patterned array of hexagonal shaped pillars with 320 μm of height and side length ∼40 μm were obtained with smooth side wall features along height. Various structural, mechanical and electrical properties of BST material after sintering were also measured to demonstrate the feasibility of the proposed aqueous processing route. [ABSTRACT FROM AUTHOR]

In this paper dielectric properties of La 2 − x Bi x Mo 2 O 9 (0 ≤ x ≤ 0.4) ionic conductors have been investigated. The frequency dependence of the dielectric permittivity and electric modulus data has been analyzed using Havriliak–Negami formalism. It has been observed that the shape parameters do not show any significant temperature dependence. The stretched exponent has been obtained from the fits of Kohlrausch–Williams–Watts function to the experimental data. The result indicates that the dielectric relaxation is highly non-exponential. Highly asymmetric decay function has been also obtained from the modulus data. [ABSTRACT FROM AUTHOR]

Three-dimensional electron backscatter diffraction technique was used for the visualization of grain boundary geometry and pore morphology in cubic zirconia. A set of four samples sintered under different conditions was investigated. Specimens which were characterized by energy dispersive spectroscopy and X-ray diffraction were entirely composed of cubic phase. Investigations of boundaries and pore structures were carried out in a dual-beam scanning electron microscope. For each sample, a volume of 1000µm³ was investigated. The analysis of grain boundary networks reconstructed from inverse pole figure maps revealed a strong dependence between grain boundary density and sample preparation parameters. Sintering also affects the size and distribution of pores. The total number of grains analyzed varied from 17 to 357 and the calculated volume of cavities from 0.01% to 21%. This paper shows the application of three-dimensional crystallographic orientation analysis to characterize the microstructure of yttria stabilized zirconia ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Our paper reports structural, magnetic and ferroelectric properties of Ni doped barium titanate. Ceramics samples of BaTi1−x Ni x O3 (here, x=0, 0.05, 0.1, and 0.15) were prepared through solid state sintering technique. It is revealed from structural studies that the phase transformation from tetragonal to hexagonal phase is strongly influenced by Ni doping concentration. Magnetism is induced in doped composition and the value of magnetism is dependent upon Ni ion concentration. This enhanced magnetic effect is likely to originate from carrier-mediated exchange interactions. Ferroelectricity was observed in all samples at room temperature, but it was decreased by Ni doping. [Copyright &y& Elsevier]

Abstract: Cerium titanate CeTi2O6 has been investigated recently for its photocatalytic activity and as a safe analogue to actinide-containing brannerite-like titanates (UTi2O6, PuTi2O6, e.g.) which are intensively studied because of their use for storing nuclear waste. In this paper we report on the monoclinic phase CeTi2O6 obtained from the Ti–Ce oxide mixture prepared by a reverse micelles directed sol–gel method and subsequently annealed. The kinetics of the isothermal crystallization process is investigated by means of Johnson–Mehl–Avrami–Kolmogorov equation. The effective activation energy of the formation of CeTi2O6 particles, which is an important parameter for its synthesis, is estimated. [Copyright &y& Elsevier]

Abstract: We have successfully prepared O/W emulsions stabilized with γ-Al2O3 nanostructures for chemical enhanced oil recovery (C-EOR). In this paper, γ-Al2O3 nanostructures with different morphology and surface area were prepared by a very simple and economical wet chemical method. The as-preparedγ-Al2O3 nanostructures were used for emulsion preparation with other ingredients such as water, suitable surfactant, n-decane and 2-propanol. It is observed that cationic surfactants (CTAB) are superior to the anionic (SDBS) and non-ionic (TX-100) surfactants and have suitable stability in different temperatures. Therefore, the as-prepared O/W emulsion can be used in chemical enhanced oil recovery (C-EOR) especially for the carbonate reservoirs. [Copyright &y& Elsevier]

Abstract: In this paper, we report the effect of morphology and solvent on the two-photon absorption of nano zinc oxide. Zinc oxide nanoparticles in two different morphologies like nanospheres and triangular nanostructures are synthesized by novel precipitation technique and their two-photon absorption coefficient is measured using open aperture Z-scan technique. Experimental results show that the zinc oxide nanospheres exhibit higher two-photon absorption coefficient than the zinc oxide triangular nanostructures. The zinc oxide nanospheres dispersed in water exhibit higher two-photon absorption coefficient than that of its dispersion in 2-propanol. The zinc oxide nanospheres dispersed in water shows a decrease in two-photon absorption coefficient with an increase in on-axis irradiance. The result confirms the dependence of shape and solvent on the two-photon absorption of nano zinc oxide. [Copyright &y& Elsevier]

Abstract: In this paper, structural and dielectric properties of BaTiO3 ceramics obtained under extreme conditions were investigated. The temperature dependent dielectric investigations revealed that the phase transition temperatures of the BaTiO3 ceramics were raised as a function of residual strains associated to the nanostructuration, while structural characterizations showed a tetragonal arrangement at room temperature. From the frequency dependence analyses of the imaginary parts of dielectric permittivity, impedance and modulus function, three relaxation processes were identified. Two of them exhibit activation energies of 0.45 and 0.63eV, and were attributed to single and double-ionization of oxygen vacancies. The whole set of results also indicated that the electrons resulting from the ionization of oxygen vacancies are trapped and do not contribute to the electrical conductivity, while the physical properties of the analyzed samples were enhanced by retaining a strained microstructure. [Copyright &y& Elsevier]

Abstract: Tungsten carbide is used in high pressure devices therefore knowledge of its elastic properties and their pressure dependence is of utmost practical importance. In this paper we present first principles results of equation of state and elastic properties of and phases of tungsten carbide and compare our results with the available reported experimental results. These calculations have been performed using the FPLAPW method within the framework of density functional theory. Enthalpies of and phases of WC have been compared up to 350GPa to investigate possibility of structural transformation. Density-dependent Grüneisen parameter has been deduced from isotherm using the well-known Slater''s formula. High pressure elastic constants of and phases of WC have been calculated by applying various distortions to the original crystal structure. The elastic properties such as bulk, shear and Young''s moduli have been derived from the calculated elastic constants. Pressure-dependent longitudinal velocity, shear velocity, Debye temperature and melting temperature have been deduced from the elastic properties. These calculated properties are in good agreement with the available experimental results. [Copyright &y& Elsevier]

Abstract: In this paper, lead-free (Na0.474K0.474Li0.052)(Nb0.948Sb0.052)O3 ceramics were synthesized by a conventional solid-state reaction route. The effects of sintering temperature on the crystal structure, microstructure, densification, dielectric properties, and ferroelectric properties of the KNNLS ceramics were addressed. X-ray diffraction patterns and Raman spectrum indicated a transition from orthorhombic to tetragonal phase during the sintering temperature region. This transition is attributed to the migration of Li between the matrix grain and grain boundary. Scanning electron microscopy study revealed increased grain size and enhanced densification with increasing sintering temperature. The density of the ceramics sintered at 1080°C reached a maximum value of 4.22g/cm3. KNNLS ceramics sintered at an optimum temperature of 1080°C exhibited high piezoelectric properties, that is 242pC/N for d 33, 0.42 for k p and 18.2μC/cm2 for P r . [Copyright &y& Elsevier]

Abstract: This paper describes research on a simple low-temperature synthesis route to prepare bismuth ferrite nanopowders by the polymeric precursor method using bismuth and iron nitrates. BiFeO3 (BFO) nanopowders were characterized by means of X-ray diffraction analyses, (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy (Raman), thermogravimnetric analyses (TG-DTA), ultra-violet/vis (UV/Vis) and field emission scanning electron microscopy (FE-SEM). XRD patterns confirmed that a pure perovskite BiFeO3 structure with a rhombohedral distorted perovskite structure was obtained by heating at 850°C for 4 hours. Typical FT-IR spectra for BFO powders revealed the formation of a perovskite structure at high temperatures due to a metal–oxygen bond while Raman modes indicated oxygen octahedral tilts induced by structural distortion. A homogeneous size distribution of BFO powders obtained at 850°C for 4 hours was verified by FE-SEM analyses. [Copyright &y& Elsevier]

Abstract: This paper describes the potential of jack bean urease to behave as a catalyst, template and assembling agent by considering its enzymatic activity, steric structure and thermostability, respectively, for the synthesis of 2D structured iron oxide and the 3D hierarchical organization of the 2D structured iron oxide. Maintaining a mixture of JBU, urea and FeCl2 at 60°C for several hours produced Fe3O4 plates; the use of denatured JBU or ammonia instead of JBU yielded spherical particles. Furthermore, the spherical particles synthesized using denatured JBU were akaganeite. These results suggest that JBU acts as both template and catalyst for the synthesis of Fe3O4 plates. In addition, the plates organize into flower-like hierarchical structures as the reaction time is lengthened, which aggregate to form spheres after 48h. The self-assembly of the plates can be controlled by tuning the denaturation of JBU, which is controlled easily because JBU is thermostable and denatures slowly. The flower-like hierarchical structures possess a relatively high saturation magnetization making them potentially useful in environmental and biomedical applications. [Copyright &y& Elsevier]

Abstract: Ultrafine powders of (Pb0.92La0.08) (Zr0.60Ti0.40)O3 (hereinafter designated as PLZT) have been synthesized from oxide powders using the high energy ball milling technique in air atmosphere. The powders milled in agate vials using Yttria stabilized Zirconia (YTZ) balls, were all about 20nm in size. XRD revealed the formation of a significant amount of the perovskite PLZT phase at room temperature itself. The bulk ceramic samples were subjected to electrical poling, prior to performing resonance measurements on them, in order to determine the piezoelectric and electromechanical coupling coefficients. Poled samples exhibited large strains under the influence of applied electric fields, with limited hysteresis. The effect of powder refinement on the structural and electrical properties of PLZT ceramics are correlated in this paper. [Copyright &y& Elsevier]

Abstract: This paper presents the effect of GeO2 glass former on the physical and electrical properties of BaFe0.5Nb0.5O3 (BFN) perovskite ceramics. The BFN powder was prepared by a conventional mixed-oxide method and the GeO2 contents, ranging from 1 to 5wt.%, were subsequently added to the calcined BFN powder. The mixtures were pressed and sintered to form dense ceramics. We showed that, with the addition of GeO2, the maximum density was achieved at lower sintering temperature, approximately 200–225°C lower than those required by the pure BFN ceramic. However, the densities of these GeO2 doped BFN ceramics were slightly lower than those of pure BFN due to the occurrence of pores. We also found that the addition of GeO2 reduces the dielectric loss at room temperature from 4.29 to 0.39–0.79 but the dielectric constant at room temperature decreased with the increased GeO2 concentrations. With small amount of added GeO2, ferroelectric property of BFN ceramics was also obtained, as confirmed by their hysteresis loops. [Copyright &y& Elsevier]

Abstract: Alumina–aluminium titanate (A–AT) composites are typically produced either by mixing the alumina matrix powder with already formed aluminium titanate or by reaction sintering of alumina and titania powders. Reaction-sintered materials usually exhibit limited final density and extensive microcracking. This paper describes the preparation of A–AT nanocomposites by slip casting and reaction sintering, using aqueous suspensions of submicrometre-sized alumina and nanometre-sized titania at a respective weight ratio of 87:13, which is typical for plasma-sprayed coatings. The colloidal stability of aqueous suspensions of the two individual powders and of their respective mixtures was determined first, measuring zeta potential and rheological behaviour as a function of deflocculant content and sonication time. The bimodal distribution yielded green relative densities of up to 70% of theoretical density. Dynamic and static sintering studies showed that aluminium titanate had already formed at 1400°C. [Copyright &y& Elsevier]

Abstract: Half doped mixed valence manganite system La0.5Ca0.45−x Sr x Ba0.05MnO3 (with x=0.1, 0.2, and 0.3) synthesized through a low temperature nitrate route is systematically investigated in this paper. The electronic transport and magnetic properties are analyzed and compared apart from the study of unit cell structure and composition. The system is found to crystallize only in orthorhombic structure (Pnma) and the electronic phase transitions are observed to be of second order. The charge and orbital ordering have been observed to coexist with ferromagnetism in x=0.1 compound. Application of small polaron and variable range hopping models to resistivity data of the system corresponding to high temperature range shows increasing mobility of e g electrons with x, with the later model describing the electronic transport very closely than the former. The temperature dependent magnetization of the compounds shows monotonic increase of paramagnetic to ferromagnetic transition (T C) with x. Ferromagnetism is exhibited for the complete temperature range down from respective T C in contrast to antiferromagnetism usually exhibited by half-doped compounds in the low temperature range. The plots of magnetization versus magnetic field reveal a transition from soft to hard magnetic character for all the compounds as the temperature is lowered. [Copyright &y& Elsevier]

Abstract: Electrospray pyrolysis, i.e. combination of electrospray and in-flight thermal treatment, has attracted much attention as a preparation method of functional ceramic particles. In this paper, we report the processing detail of spherical TiO2 nano- and microparticles by the electrospray pyrolysis method as well as their photocatalytic activity for hydrogen evolution. Titanium(IV) bis(ammonium lactato)dihydroxide aqueous solutions (TALH aq., 0.2–20wt%) were injected into a capillary nozzle by a syringe pump (0.15–0.59mL/min), and were electrosprayed by using DC 4kV voltage, followed by the pyrolysis at 300–500°C. Spherical TiO2 nano- and microparticles were successfully obtained. Effects of precursor-liquid concentration, liquid flow-rate, and pyrolysis temperature on the particle size, microstructure and functions were discussed. [Copyright &y& Elsevier]

Abstract: In this paper, we report on the preparation, dielectric and magnetic properties of Ba5NdNiNb9O30 ceramics and its structural refinement. Ba5NdNiNb9O30 powders were synthesized by solid state reaction at 1350°C for 3h. X-ray diffraction and Rietveld refinement analysis revealed that the ceramics present a single phase with tetragonal tungsten bronze structure in space group P4bm. Broad dielectric peaks with strong frequency dispersion were observed in the temperature range from 150 to 230K. The frequency dependence of the dielectric maximum temperature well follows the Vogel–Fulcher relationship and the relaxor behavior can be well fitted with the modified Curie–Weiss law with a diffusivity parameter value of 1.69 at 1kHz. The temperature dependence of magnetization suggests the absence of a long-range magnetic ordering while a negative paramagnetic temperature θ Weiss indicates the presence of weak antiferromagnetic interactions. [Copyright &y& Elsevier]

Abstract: In this paper we report the structural, magnetic, magnetocapacitance and dielectric properties of BiFe1−x Ni x O3 nanoceramics (with x=0, 0.1) prepared by the sol-gel method. XRD analysis showed formation of single phase nanoceramics (particle size ∼50nm by TEM). Samples of BiFe1−x Ni x O3 were divided into two parts—one of them quenched in liquid nitrogen and another sintered in the normal way. We observed the enhancement in magnetic and dielectric properties of quenched sample. The splitting of zero field cool (ZFC) and field cool (FC) magnetization curves at low temperature reveals spin- glass behavior. Quenched sample showed the enhancement of blocking temperature. [Copyright &y& Elsevier]

Abstract: Many studies have been performed dealing with the processing conditions of electrodes and electrolytes in solid oxide fuel cells (SOFCs). However, the processing of the interconnector material has received less attention. Lanthanum chromite (LaCrO3) is probably the most studied material as SOFCs interconnector. This paper deals with the rheology and casting behaviour of lanthanum chromite based materials to produce interconnectors for SOFCs. A powder with the composition La0.80Sr0.20Cr0.92Co0.08O3 was obtained by combustion synthesis. Aqueous suspensions were prepared to solids loading ranging from 8 to 17.5vol.%, using ammonium polyacrylate (PAA) as dispersant and tetramethylammonium hydroxide (TMAH) to assure a basic pH and providing stabilization. The influence of the additives concentrations and suspension ball milling time were studied. Suspensions prepared with 24h ball milling, with 3wt.% and 1wt.% of PAA and TMAH, respectively, yielded the best conditions for successful slip casting. Sintering of the green discs was performed in air at 1600°C for 4h leading to relatively dense materials. [Copyright &y& Elsevier]

Abstract: Lanthanum based mixed valence manganite system La1−x Ca x−0.08Sr0.04Ba0.04MnO3 (LCSBMO; x=0.15, 0.24 and 0.33) synthesized through the sol–gel route is systematically investigated in this paper. The electronic transport and magnetic susceptibility properties are analyzed and compared, apart from the study of unit cell structure, microstructure and composition. Second order phase transition is observed in all the samples and significant difference is observed between the insulator to metal transition temperature (T MI ) and paramagnetic (PM) to ferromagnetic (FM) transition temperature (T C ). In contrast to the insulating FM behaviour usually observed in La1−x Ca x MnO3 (LCMO) for x=0.15, a clear insulator to metal transition is observed for LCSBMO for the same percentage of lanthanum. The temperature dependent resistivity of polycrystalline pellets, when obeying the well studied law ρ=ρ o +ρ 2 T 2 for TT MI . AC magnetic susceptibility study of the polycrystalline powders of the manganite system shows the highest PM to FM transition of 285K for x=0.33. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on multiferroic properties of Ho substituted BiFeO3 (Bi1−x Ho x FeO3) ceramics. It is observed that for x=0.15, a prominent ferroelectric loop is seen at 300K even if the system remains in rhombohedral (R3c) phase without appearance of any observable impurity phases. A well shaped M–H loop is observed at 10K for x=0.15. However it showed ferromagnetism, confirming the contribution of Ho3+ towards enhancement of ferromagnetic properties of BiFeO3 at 300K. Suppression of impurity phases of pure BiFeO3 bulk ceramic favors the reduction of mobile oxygen vacancies and reduces leakage current, due to which ferroelectric properties of BiFeO3 is enhanced. We argue that Ho substitution at Bi site is likely to suppress the spiral spin modulation and at the same time increase the canting angle, which favors enhanced multiferroic properties. XRD, SEM, magnetization, polarization and chemical bonding analysis measurements were carried out to explain the multiferroic behavior. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the effects of processing densification on the mechanical properties of hydroxyapatite bioceramics. Densification of synthetic hydroxyapatite is conducted in the range 1000–1300°C. X-ray diffraction and SEM microscopy are used to check the microstructure transformations. Vickers hardness, toughness and Young''s modulus are analyzed versus the density and grain size. The sintering temperature and the particle size influence strongly the densification and the resulting mechanical properties. In addition, the critical sintering temperature appears around 1200°C and the declined strength at the temperature up to 1200°C is found sensitive to the dehydroxylation process of hydroxyapatite. [Copyright &y& Elsevier]

Abstract: This paper reports the results of the thermal stability study of M–YSZ (M=Ni, Cu, Co, Cu–Co, Ni–Cu–Co) SOFC anode cermets materials at different heat treatment temperatures. The cermets were elaborated by atmospheric plasma spraying (APS) with optimized conditions and then submitted to heat treatments at 800 and 1000°C, respectively. Scanning electron microscopy and X-ray diffraction were used to characterize, respectively, the morphology and structure of obtained films, before and after thermal annealing. A correlation was made between the differential scanning calorimetry analysis results and those obtained by X-ray diffraction. Focusing, in this study, on YSZ matrix thermal stability, the obtained results were as follows: the monometallic cermets with the lowest amount of metal and the trimetallic one exhibited a good stability at 800°C, whereas at 1000°C, all considered cermets were unstable with a eutectoid decomposition of YSZ matrix. [Copyright &y& Elsevier]

Abstract: Even though the PZT ceramic system has been thoroughly studied and modified with different additives, no numerous reports have been published focusing on the PZT double ‘soft’ modification with La3+ and Nb5+ (PLZTN). In this paper, we explore the structural, morphological, dielectric, ferroelectric and piezoelectric properties of the PLZTN system for different doping levels (x La3+ = x Nb5+ =0.4, 0.6, 0.8, 1.0 and 1.4at.%) synthesized by conventional powders reaction. The temperature dependence of the piezoelectric response of poled ceramic disks is also analyzed and, according to its overall features, an optimum modification is proposed in order to develop PZT-based sensors for several applications. [Copyright &y& Elsevier]

Abstract: Ag-doped BaTiO3 based X7R (temperature coefficient of capacitance within the range of ±15% between −55 and +125°C) ceramics with different amounts of silver (0.0–20.0mol%) were prepared in this paper. The X-ray diffraction analysis indicated that no phases other than BaTiO3 and silver were observed in the ceramics. The energy dispersive X-ray spectroscopy analysis showed that the silver particles presented homogeneous distribution in the BaTiO3 ceramics. The dielectric properties of Ag-doped ceramics were investigated. A small amount of silver (<0.5mol%) and a large amount of silver (>2.0mol%) could both improve the sintered density and permittivity, but more content of silver (0.5–2.0mol%) would decrease the relative density and permittivity. Specially, the temperature coefficient of capacitors of the ceramics doped with 20mol% silver still met the X7R characteristics, and the room temperature permittivity of the ceramics was 6823, which was the highest dielectric constant in the BaTiO3 based X7R ceramics. [Copyright &y& Elsevier]

Abstract: In this paper, Pb0.55−(3 y /2)Ce y Ba0.45Nb2O6 ceramics with tetragonal tungsten–bronze structure prepared through the solid-state reaction method and characterized for phase formation, density, dielectric and piezoelectric properties are reported. The XRD analysis showed the presence of a tetragonal tungsten–bronze structure, which intensified with increasing Ce content. The stability of the tetragonal tungsten–bronze phase has been discussed with the electronegativity difference and the tolerance factor. The Curie temperature (T c) systematically lowered when Ce was incorporated into tetragonal PBN lattice. The room-temperature dielectric constant (ε RT) of Ce-modified lead barium niobate (PBN) compositions has enhanced from C0 to C3 and thereafter decreased. The influence of Ce on piezoelectric properties of tetragonal PBN system has been evaluated. The piezoelectric coefficients (d, g, k and Q m) were characterized. The C3 composition exhibited optimum piezoelectric properties in the series, and this composition could be suitable for piezoelectric applications. [Copyright &y& Elsevier]

Abstract: Synthetic hydroxyapatites incorporating small amounts of Si have shown improved biological performances in terms of enhanced bone apposition, bone in-growth and cell-mediated degradation. This paper reports a systematic investigation on Si-substituted hydroxyapatite (Si 1.40wt%) nanopowders produced following two different conventional wet methodologies: (a) precipitation of Ca(NO3)2·4H2O and (b) titration of Ca(OH)2. The influence of the synthesis process on composition, thermal behaviour and sinterability of the resulting nanopowders is studied. Samples were characterised by electron microscopy, induced coupled plasma atomic emission spectroscopy, thermal analysis, infrared spectroscopy, N2 adsorption measurements, X-ray diffraction and dilatometry. Semicrystalline Si-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 84 and 110m2/g. Pure and Si-substituted hydroxyapatite nanopowders derived from Ca(NO3)2·4H2O decomposed around 1000°C. Si-substituted hydroxyapatite nanopowders obtained from Ca(OH)2 were thermally stable up to 1200°C and showed a distinct decreased thermal stability with respect to the homologous pure sample. Si-substituted hydroxyapatites exhibited higher sintering temperature and increased total shrinkage with respect to pure powders. Nanostructured dense ceramics were obtained by sintering at 1100°C Si-substituted hydroxyapatites derived from Ca(OH)2. [Copyright &y& Elsevier]

Abstract: In this paper, the sol–gel synthesis and characteristic properties of kalsilite-type alumosilicates (KAlSiO4 and K0.5Na0.5AlSiO4) are reported. The polycrystalline powders were characterized by thermal analysis (TG/DTA), powder X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Single-phase kalsilite oxides have been obtained after annealing precursor gels for 5h in the temperature range of 750–850°C. It was demonstrated that crystallinity of the samples slightly depends on the temperature of annealing. From the results obtained, it could be concluded that the KAlSiO4 solids are composed of the volumetric plate-like grains with no regular size (from 5μm to 30μm at 750°C and around 5–50μm at 850°C). Larger crystallites for mixed potassium–sodium kalsilite have formed (from 10μm to 80μm at 750°C and >100μm at 850°C) in comparison with potassium kalsilite samples). The erosion of obtained dental porcelain samples stored in saliva, beer and Coca-Cola was compared. [Copyright &y& Elsevier]

Abstract: This paper reports the characterization of nanocrystalline ZnO powders synthesized by a precipitation method and annealed with carbon black. The X-ray diffraction (XRD) and Fourier Transformed Infrared (FT-IR) results revealed that the synthesized ZnO powder has the wurtzite structure with absorbed CO3 − species on the surface of the ZnO particles. Singly ionized oxygen vacancy (VO +) and CO3 − species were also perceived from electron paramagnetic resonance (EPR) analysis. The intensity of the EPR signals of CO3 − species increased as the amount of carbon increased whereas that of VO + did not vary significantly. A green emission at 528nm for the powders annealed with carbon was observed and a good correlation between the intensity of green emission and the intensity of EPR signals of CO3 − was obtained Experimental results suggest that the formation of the free carriers has significant effect on the intensity of the green emission. The mechanism responsible for the green emission enhancement based on the relevance of the observations is discussed. [Copyright &y& Elsevier]

Abstract: This paper describes a new class of alumina composites based on a novel hybrid microstructure design, in which multiwalled carbon nanotubes (MWNTs) and SiC nanoparticles are combined to give a new type system of ceramic nanocomposites. This design provides mutually redundant mechanisms to enhance the strength and toughness of the alumina matrix without deteriorating its intrinsic properties such as hardness. The hybrid alumina composites with different MWNT contents (0, 5, 7, and 10vol%) and 1vol% of SiC were fabricated by spark plasma sintering. The resulting significant improvement in mechanical properties, specially the fracture toughness, is substantiated by direct evidence for toughening mechanisms by MWNTs, observed for the first time in highly disordered MWNT/alumina composites. [Copyright &y& Elsevier]

Abstract: This paper reports the synthesis and electromechanical characterization of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN–35PT) ceramics and fibers. To prevent the lead loss during the sintering of the fibers, lead-atmosphere was used during the sintering process. As a consequence, it was possible to ensure a good densification of the fiber and a pure perovskite phase. The electromechanical coupling factor and piezoelectric coefficient of the piezoelectric fiber were found to be k 31 =0.20 and d 31 =−130pC/N, respectively. These results are lower than ceramic sample properties (k 31 =0.32 and d 31 =−234pC/N). In order to determine reasons for these lower results in fiber shape sample, density and poling studies were performed. It is shown that fiber shape samples cannot be poled correctly because of the ratio between core and ceramic diameters. [Copyright &y& Elsevier]

Abstract: In this paper, an interconnecting ceramic for solid oxide fuel cells was developed, based on the modification from La0.7Ca0.3CrO3−δ by addition of Ce0.8Sm0.2O1.9. It is found that addition of small amount Ce0.8Sm0.2O1.9 into La0.7Ca0.3CrO3−δ dramatically increased the electrical conductivity. For the best system, La0.7Ca0.3CrO3−δ +5wt.% Ce0.8Sm0.2O1.9, the electrical conductivity reached 687.8Scm−1 at 800°C in air. In H2 at 800°C, the specimen with 3wt.% Ce0.8Sm0.2O1.9 had the maximal electrical conductivity of 7.1Scm−1. With the increase of Ce0.8Sm0.2O1.9 content the relative density increased, reaching 98.7% when the Ce0.8Sm0.2O1.9 content was 10wt.%. The average coefficient of thermal expansion at 30–1000°C in air increased with Ce0.8Sm0.2O1.9 content, ranging from 11.12×10−6 to 12.46×10−6 K−1. The oxygen permeation measurement illustrated a negligible oxygen ionic conduction, indicating it is still an electronically conducting ceramic. Therefore, this material system will be a very promising interconnect for solid oxide fuel cells. [Copyright &y& Elsevier]

Abstract: Tricalcium phosphate based ceramics (TCP) are bioresorbable and thereby considered to be promising bone replacement materials. The differences in crystal structure between α and β-TCP phases gives rise for different dissolution rates in vitro and in vivo, which may alter the bioresorbable behavior of TCP ceramics. It is suggested that the addition of magnesium ions, which are also present in biological tissues, stabilizes β-phase to higher temperatures and thus enables the sintering of β-TCP at elevated temperatures compared to Mg free TCP. In this paper, Mg-substituted TCP, with the general formula (Ca1−x Mg x )3(PO4)2 and 0.01≤ x ≤0.045, were produced by wet chemical synthesis from Ca(OH)2, H3PO4 and MgO, after calcinations at three different temperatures between 750 and 1050°C. The influence of different amounts of Mg substitution on the physical properties, microstructure, and sintering behavior of calcium phosphate powders was evaluated. Thermal analytical techniques, together with X-ray diffraction analysis, were successfully combined in order to characterize the occurring phase transformations during annealing of the powders. The results show that the addition of small amounts of Mg (up to 1.5mol%) are adequate to postpone the β–α TCP phase transformation to 1330°C and to accelerate the densification process during sintering of β-TCP ceramics. [Copyright &y& Elsevier]

Abstract: This paper presents a synthesis of TiB2 powder via self-propagating high-temperature synthesis (SHS) method using a mixture of TiO2, B2O3 and Mg followed by acid leaching. In the acid leaching step, the MgO content in the SHS product was leached in different HCl concentrations. X-ray diffraction (XRD) analysis showed that when 9.3M HCl was used, the leached SHS product was found similar to that of the commercial TiB2 powder. However, scanning electron microscopy (SEM) and BET surface area analysis revealed that the leached product was agglomerated and exhibited very high surface area. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate and report the effects of a cationic polyelectrolyte, polydiallydimethylammonium chloride (PDADMAC), on the stability of nano-sized alumina (α-Al2O3) suspension. Due to the static electrical repulsion interactions, PDADMAC show significant adsorption on α-Al2O3 only at alkaline pH. Considerable amount of non-adsorbed free PDADMAC exist in α-Al2O3 suspensions dispersed by PDADMAC at acidic and neutral pH. At 1.0wt.% PDADMAC addition, α-Al2O3 became highly positively charged (>50mV) in the entire pH range contrast with that the stability of α-Al2O3 suspension is enhanced only over the basic pH range in the presence of anionic polyelectrolyte. Free PDADMAC electrolyte in suspension results in increasing viscosity of α-Al2O3 suspensions dispersed with PDADMAC at alkaline and neutral pH. However, non-adsorbed free PDADMAC in suspension do not contribute to viscosity increase in acidic α-Al2O3 suspensions and α-Al2O3 suspensions dispersed with PDADMAC show the best flow behavior at acidic pH. [Copyright &y& Elsevier]

Abstract: In this paper, we solve numerically the coupled conduction–radiation heat transfer problem in semi-transparent orthotropic materials. Both the conduction and the radiation problems are solved with finite-volumes. The numerical solution obtained here is validated with results available in the literature. Results are presented for test cases involving the non-uniform heating of bodies at high-temperatures. [Copyright &y& Elsevier]

Abstract: In this paper, (Ca+Yb)- and (Ca+Sr)-stabilized α-SiAlON powders were fabricated by combustion synthesis. The influence of Ca2+ incorporation on the phase composition and grain morphology of combustion products was discussed. The experimental results showed that with the incorporation of Ca2+ well-developed rod-like (Ca+Yb) α-SiAlON crystals could be produced. It was also found that, when only Sr2+ was used as stabilizing cation, the reaction product was (α+β)-SiAlON composite, in which β-SiAlON was the predominant phase and the relative content of α-SiAlON was low. With the incorporation of Ca2+, however, both the relative content and the lattice parameters of α-SiAlON were clearly increased. These results indicated that the incorporation of Ca2+ could assist Sr2+ into the α-SiAlON lattice structure. [Copyright &y& Elsevier]

Abstract: The sintering behavior, microstructure and microwave dielectric properties of complex pyrophosphate compounds AMP2O7 (A=Ca, Sr; M=Zn, Cu) were investigated in this paper. All compounds could be densified below the temperature of 950°C without any glass addition, and exhibit low permittivity (ɛ r <8), high Q × f value and negative temperature coefficient of resonant frequency. The Q × f value was discussed from the point of view of bond strength. The chemical compatibility with silver and copper was also investigated. All compounds seriously react with silver at ∼700°C. However SrZnP2O7 could be co-fired with copper in reduced atmosphere. The microwave dielectric properties of SrZnP2O7 sintered at 950°C in reducing atmosphere are: ɛ r =7.06, Q × f =52781GHz, τ f =−70ppm/°C. In terms of its lower sintering temperature, chemical compatibility with copper and good microwave dielectric properties, SrZnP2O7 ceramic is very promising for low temperature co-fired ceramic (LTCC) applications. [Copyright &y& Elsevier]

Abstract: This paper deals on a study realized in order to elaborate dense ceramic of Bi4La2O9 oxide conductor. A wet method in nitric media, usually favorable to obtain low grain size, did not allow to isolate the stable phases. Material with particle low size has been obtained by attrition treatment after conventional solid state powder synthesis. The decrease of particle size (≅4 times), evidenced by X-ray diffraction and SEM, influences the reversibility of transitions between monoclinic ɛ and rhombohedral β2 varieties on powder, as well as ceramics, leading to an improvement of the conductivity level of these ones after a thermal cycle. [Copyright &y& Elsevier]

Abstract: In this paper, the feasibility of synthesizing NiCuZn ferrite powders by combustion synthesis (CS) reaction is demonstrated through igniting the mixtures of iron, iron oxide, copper oxide, zinc oxide and copper carbonate under different oxygen pressure values. The ferrite powders produced directly from the CS reaction and after annealing at 800°C for 2h are characterized by XRD, SEM, XPS and VSM. The results show that the spinel phase in the combustion products increases with the decrease of the diluent content and the increase of the oxygen pressure. Heating the as-synthesized ferrite at 800°C for 2h affords pure crystalline NiCuZn ferrite, which possesses better magnetic properties. XPS studies confirm that copper ions in the as-synthesized ferrite are present in the different ionic states of the A- and B-sites, while copper ion is divalent in the B-sites only for the annealed products. [Copyright &y& Elsevier]