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Pressureless sintering is a well-established powder metallurgical route for processing and consolidation of mixed materials. Especially materials exhibiting a high melting point could be densified without tool abrasion by this sintering technique. As the sintering temperatures are often higher compared to pressure-assisted techniques care must be taken by means of grain growth. In our studies we used a ternary compound mixture to obtain Mo-based alloys. Consolidation applying pressure-assisted methods (hot pressing, spark plasma sintering) and pressureless sintering were used, respectively. The densities reached and the microstructures obtained were compared. These Mo-Si-B alloys were processed using a nitride-powder-based route offering lower impurity contents due to short processing times by avoiding time consuming mixing / milling steps. The sintering conditions depending on the powder particle size as well as the sample shape will be presented in detail. The composition investigated in this article offered a continuous a-Mo matrix with intermetallic islands consisting of Mo3Si and Mo5SiB2 (T2) phases. The combination of a ductile a-Mo matrix and intermetallic phases embedded within offered an enhanced mechanical behavior at room temperature compared to MoSi2 or other intermetallic alloys. Moreover, the intermetallic compounds as well as Mo are candidates for high-temperature applications. As the high-temperature behavior could be strongly influenced by the respective microstructure we present here the processing and the microstructure obtained.

The subsolidus phase relations of the BaO–Y2O3–MnO2 system have been investigated in air. There are eight binary compounds, a new ternary compound and 11 three-phase regions in this system. The ternary compound with the BaO:YO1.5:MnO2 molar ratio of 8:2:5 was indexed by a rhombohedral lattice with a = 5.7929 (6) and c = 28.586 (4) A. The synthesized compounds were determined to be stoichiometric except for the Ba1−xYxMnO3 phase (x ≤ 0.01).

Highly concentrated slurry preparation and low-temperature pressureless sintering of SiC using a novel Al3BC3 additive were investigated. Al+B4C+C powder mixture, which is a conventional sintering additive system of SiC, could not be dispersed in ethyl alcohol above 10 vol%. In contrast, Al3BC3 slurry (average particle size: 0.5 μm) could be prepared up to 50 vol% solid loading and SiC slurry containing 10 wt% Al3BC3 was successfully fabricated up to 45 vol%. The relative density of SiC was 97.9% after pressureless sintering at 1850°C. Young's modulus and hardness of a sintered SiC were 411 and 22.5 GPa, respectively. The present report proposes a method for the low-temperature pressureless sintering of SiC specimens having complex shape and fair mechanical properties by the application of a ternary compound (Al3BC3) as a novel-sintering additive.

A new compound, Na2Zn5(PO4)(4), was identified in the system ZnO-Na2O-P2O5 and high-quality crystal was obtained by the melt method. The crystal structure of this compound was solved by direct method from single crystal X-ray diffraction data. The structure was then refined anisotropically using a full-matrix least square refinement on F-2 and the refinement converged to R-1 = 0.0233 and wR(2) = 0.0544. This compound crystallizes in the orthorhombic system with space group Pbcn, lattice parameters a=10.381(2) angstrom, b=8.507(1) angstrom, c = 16.568(3) angstrom and Z = 4. The structure is made up of 3D [Zn5P4O16](n)(2n-) covalent framework consisting of [Zn4P4O16](n)(4n-) layers. The powder diffraction pattern of Na9Zn21(PO4)(17) is explained by simulating a theoretical pattern with NaZnPO4 and Na2Zn5(PO4)(4) in the molar ratio of 1:4 and then by Rietveld refinement of experimental pattern. Na2Zn5(PO4)(4) melts congruently at 855 degrees C and its conductivity is 5.63 x 10(-9) S/cm. (C) 2007 Elsevier Inc. All rights reserved.

Deformation and cracking behavior of Ge–Sb–Se binary and ternary chalcogenide glasses of varying average covalent coordination number, 〈r〉, was studied by indenting with Vickers and Brinell microindenters using static and recording machines, and subsequent analysis using a non-contact profilometer. Vickers-produced cracks were the smallest around the GeSe4 composition (〈r〉=2.4) after unloading, hence the indentation toughness was a maximum and the brittleness a minimum at 〈r〉=2.4. Brinell-created pond (crater) depth, the mound (pile-up) height, and the radial fractures originating from the mounds displayed minima in the binaries, presumably due to maximized elastic recovery around 〈r〉=2.4. Consequently, Brinell hardness computed from the unloaded depth (HBD) showed a maximum around GeSe4. The maximized elastic recovery around GeSe4 is consistent with Phillips' optimized connectivity arguments. GeSe4 resembles the “anomalous” SiO2 glass for deformation and cracking behavior. Surprisingly, many of the extrema were nearly non-existent in the ternary glasses. The apparent contrast to the binary glasses is not understood.

Monosized strontium titanate (SrTiO 3 ) particles with tailored morphologies have been successfully synthesized using ultrasound irradiation. Characterization techniques such as X-ray powder diffraction analysis, scanning electron microscopy, energy-dispersive analysis of X-rays, and laser particle size analysis were used to investigate the products. The results showed that all the as-prepared powders have a cubic SrTiO 3 structure. Reaction conditions such as reactant concentrations, sonication time, and sonication power were found to have important effects on the morphology of SrTiO 3 particles.

A layer-by-layer method is used to coat silica on the red phosphor powders of Y 2 O 2 S:Eu in aqueous solutions. A cationic polymer of polyethylenimine (PEI) is used to form the first-layer coating, and the precipitating sodium silicate solution, to form negatively charged silica film on the PEI-coated phosphor powder as the second-layer coating. Repetition of the above coating process in aqueous solutions, a uniform, multiple silica/PEI bilayer coating on phosphor powder is formed.

Uniform spherical powders of Ce 0.9 Gd 0.1 O 1.95 with an average diameter of 250 nm were obtained at 700°C from a sol-gel process of mixing nitrates and ethylene glycol. Broadening of the X-ray peaks of the fluorite structure reveals a small crystallite size within the powders. Sintering in air of pressed pellets of the powders at 1585°C gives ceramics of 99% theoretical density with grain sizes 1-10 μm and a cubic unit cell a = 5.422 ± 0.034 A. The electrical conductivity σ = σ o + σ e has two components. In air or argon, the electronic component σ e is negligible and the oxide-ion conductivity σ o is not described by a classical Arrhenius equation; a pronounced curvature at T T * has been observed in the Arrhenius plot of the bulk conductivity. The system could be modeled by a condensation of mobile oxygen vacancies into ordered clusters below a temperature T* 583 ± 45°C and a motional enthalpy ΔH m = 0.63 ± 0.01 eV for the vacancies. A measured trapping energy ΔH t (I - T/T * ) has ΔH t = 0.19 ± 0.01 eV = 2.57kT*. In a reducing atmosphere, σ e exhibits a small-polaron motional enthalpy ΔH P = 0.40 ± 0.08 eV for transfer of a 4f electron from a Ce 3+ to a Ce 4+ ion and a ΔH p + ΔH pt = 0.51 ± 0.04 eV at T < T*.

The binary compounds Ca3Al2O6 (C3A), Ca12Al14O33 (C12A7), CaAl2O4 (CA), CaAl4O7 (CA2), and CaAl12O19 (CA6) in the CaO-Al2O3 system have been synthesized as high-compound-purity ceramic powders by using the self-propagating combustion synthesis (SPCS) method. Materials characterization of the above-mentioned phases was performed via powder X-ray diffractometry (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The structural characterization of the C12A7 phase has been performed via Rietveld analysis on the powdered XRD samples. It has hereby been shown that, by using this synthesis procedure, it should be possible to manufacture high-purity ceramic powders of CA, CA2, and C12A7 at 850°C, C3A at 1050°C, and CA6 at 1200°C in a dry-air atmosphere.

In the present study, the incongruent dissolution of barium from barium titanate (BaTiO 3 ) has been studied as a function of dispersion pH and powder volume fraction for two different BaTiO 3 powders. In alkaline dispersions, the barium solubility strongly increases as the pH increases, as suggested by thermodynamic considerations. At pH

This article gives a historical account of the development of spinel electrodes for rechargeable lithium batteries. Research in the late 1970s and early 1980s on high-temperature Li/Fe3O4 cells led to the evaluation of lithium spinels Li[B2]X4 at room temperature (B = metal cation). This work highlighted the importance of the [B2]X4 spinel framework as a host electrode structure and the ability to tailor the cell voltage by selection of various B cations. Examples of lithium-ion cells that operate with spinel anode/spinel cathode couples are provided. Particular attention is given to spinels within the solid-solution system Li1+xMn2-xO4 (0 lessthan equal to x lessthan equal to 0.33).

The oxidation kinetics of hot-pressed Mo(Al0.01Si0.99)2 and Mo(Al0.1Si0.9)2 were measured at 480°C, and between 1200° and 1600°C. The qualitative oxidation of arc-melted Mo(Al0.1Si0.9)2, Mo(Al0.3Si0.7)2, Mo(Al0.5Si0.5)2, and Mo3Al8 was examined after 600°C for 1000 h in air. At all temperatures, the compositional difference between the materials yielded very different oxidation rates and scale microstructures. At 1400° and 1500°C, microstructural evolution of the oxide scales resulted in improved oxidation resistance at long times (>400 h). At these temperatures, a significant reduction in the long-time oxidation kinetics was correlated with the in situ formation of an inner mullite scale. At 480° and 600°C, oxidation resistance improved significantly with increasing aluminum concentration. Contrary to the behavior of MoSi2, samples of Mo(Al0.01Si0.99)2 did not demonstrate catastrophic oxidation, and samples of Mo(Al0.1Si0.9)2 were very oxidation resistant.

The ternary compound Ho2MnxTa2−xO7 was synthesized in air at 1523 K. Structural characterization of the compound was taken by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The compound possessed a trigonal super cell derived from a rhombohedral basic cell with the a/2 of the trigonal super cell. The super cell was caused by the ordering of Mn and Ta ions and the derived structure model was in agreement with that of the zirkelite structure with the space group P3121. The compound had stacking disorder with different stacking sequences along the c-axis. An orientation anomaly in the super cell reflections revealed that the super cell had an incommensurate nature.

Dissolution of BaCO 3 and its effect on the dispersion behavior of aqueous BaCO 3 suspensions at various pH values have been investigated. The amount of leached Ba 2+ decreases with increasing pH value, which agrees with thermodynamically calculated results. The dissolution of BaCO 3 also causes an increase in pH value of the suspension, but the change decreases with increasing initial pH value. The isoelectric point (IEP) of leached BaCO 3 powder is at a pH of ∼10-10.5 and remains unchanged with increasing solids loading. The IEP of BaCO 3 shows no significant change with added KCI or K 2 CO 3 , but shifts to a higher pH with increasing concentration of added BaCl 2 .

The ternary compound Er2Mn2/3Mo4/3O7, with a pyrochlore-related structure, was synthesized in a vacuum-sealed quartz tube at 1373 K. The compound was characterized by X-ray diffractometry, electron probe microanalysis, and transmission electron microscopy. The compound possessed a monoclinic structure, with lattice parameters of a= 1.2781(2) nm, b= 0.7378(5) nm, c= 1.1643(6) nm, and β= 100.53(1)°. The compound had a large number of lamellar domains, which were composed of a microtwinned structure on the twin axis 〈1¯1¯0〉.

Hydrothermally synthesized barium titanate, BaTiO 3 (commercially available), has internal pores in small particles. The three-dimensional structures of the pores were successfully observed using transmission electron microscopy (TEM) and reconstructed by a tomography system. The behavior of the internal pore is observed in situ with increasing temperature on the thermal stage of a TEM device. We succeed in recording the movement of pores and small grains. At >1128 K, some pores move out from the particle's surface during TEM observation. The temperature roughly agrees with the temperature at which the density of BaTiO 3 powder sharply increases. During observation with increasing temperature, a thin layer appeared on the particle's surface at >73 K and then disappeared at 1193 K.

A solid-state reaction process has been developed to synthesize perovskite-type LaCoO 3 nanocrystals with grain diameters of 15-40 nm. In the first step of the preparation, ∼5 nm composite hydroxide nanoparticles are synthesized by the solid-state reaction of La(NO 3 ) 3 .nH 2 O and Co(NO 3 ) 2 .6H 2 O with KOH at ambient temperature. A perovskite-type rhombohedral LaCoO 3 phase appears at 550°C, after the hydroxide has been calcined at various temperatures. The phase transformation process is complete at ∼800°C, yielding a single-phase binary oxide. The results indicate that the new process is convenient, inexpensive, and effective for obtaining LaCoO 3 nanocrystals with high yield.

Atomistic simulation techniques have been used to model the dissociative adsorption of water onto the low-index {100}, {110}, and {111} surfaces of spinel MgAl2O4. The Born model of solids and the shell model for oxygen polarization have been used. The resulting structures and chemical bonding on the clean and hydrated surfaces are described. The calculations show that the dissociative adsorption of water on the low-index surfaces is generally energetically favorable. For the {110} and {111} orientations, the surfaces cleaved between oxygen layers show high absorption and stability. The calculations also show that, for the {111} orientation, the surfaces may absorb chemically water molecules up to ∼90% coverage and have the highest stability. It is suggested that, during fracture, only partial hydration occurs, leading to cleavage preferentially along the {100} orientation.

In this paper, a simple hydrothermal route has been developed to synthesize ZnCr2O4 nanoparticles. Experimental results show that the as-prepared ZnCr2O4 nanoparticles have an average particle size of

A simple co-precipitation technique was successfully used for the preparation of pure ultra fine, single-phase LaNbO 4 (LN). Aqueous sodium hydroxide was used to precipitate La 3+ and Nb 5+ cations as hydroxides simultaneously under basic conditions. For comparison, LN powders were also prepared by the traditional solid-state method. It is observed that the co-precipitation technique produces LaNbO 4 on heating at temperatures as low as ∼300°C, whereas complete phase formation occurs only at 900°C or higher in the solid-state method. The phase contents and lattice parameters were studied using powder X-ray diffraction (XRD). The XRD results show that phases obtained by both methods were different. The average particle size and morphology of these powders were analyzed by scanning electron microscope.

This paper reports the synthesis of technologically important ferrites such as ZnFe 2 O 4 , NiFe 2 O 4 , MnFe 2 O 4 , and CoFe 2 O 4 by using novel microwave-hydrothermal processing. Nanophase ferrites with high surface areas, in the range of 72-247m 2 /g, have been synthesized in a matter of a few minutes at temperatures as low as 164°C. The rapid synthesis of nanophase ferrites via an acceleration of reaction rates under microwave-hydrothermal conditions is expected to lead to energy savings.

A novel ceramic synthesis technique, combustion synthesis, was explored to produce red-emitting Cr{sup 3+}-doped Y{sub 3}Al{sub 5}O{sub 12} and Eu{sup 3+}-doped Y{sub 2}O{sub 3} phosphors with improved physical and luminescent properties. This technique involves the reaction of metal nitrates (oxidizers) and an organic fuel (urea, carbohydrazide, glycine) at 500 C. Resulting powders are well-crystallized, with a large surface area and small particle size. The spectral energy distribution was observed using photoluminescence measurements. The effects of processing parameters such as type of fuel, fuel-to-oxidizer ratio, furnace temperature, and batch water content were studied. An increase in phosphor brightness with increasing reaction temperature was observed. Postreaction heat treatments (1000, 1300, and 1600 C) increased the luminous intensity of as-synthesized powders. Residual carbon content and chromium site symmetry were investigated as possible explanations for the increase in brightness with increasing heat treatment temperature. By tailoring the reaction chemistry, the optimal conditions for producing the most luminescent phosphors have been identified.

In this investigation, several experiments have been conducted to study the effects of temperature and atmosphere on the formation of BaTiO3 using the citrate process. It was found that BaTiO3 could be completely formed when the precursor powder was heated at 300°C in O2 for 24 h and then heated in situ at 475°C for 1 h, during which no intermediate phase was observed throughout the process. Moreover, BaTiO3 could be formed at 400°C in O2 via the combustion of organic materials, in which the amount of the residual BaCO3 depended on the partial pressure of O2. The development of BaCO3 and oxycarbonate intermediate was found to be dependent on the temperature, the atmosphere, and the organic materials, and their formation mechanisms are discussed.

A precursor for Y3Al5O12 was synthesized as a YAG sol by simply dissolving Y2O3 powder in an alumina sol. Phase-pure Y3Al5O12 powder was obtained by precipitating the YAG sol with an aqueous dilute ammonia solution followed by calcination at 1100°C. TG/DTA analysis showed an exotherm at 938°C attributed to formation of YAG phase and weight loss of 44% at 1000°C. XRD and FT-IR analysis showed that phase-pure YAG can be formed through noncrystalline and metastable hexagonal YAlO3 without forming either yttrium or aluminum formate intermediate.

Crystalline, submicrometer strontium ferrite powders, including SrFeO2.97, SrFe2O4, Sr2FeO4, Sr3Fe2O6.16, and SrFe12O19, were prepared by spray pyrolysis of an aqueous solution of mixed metal nitrates. The Sr:Fe mole ratio in the precursor solution was retained in the final products. Phase-pure materials were typically obtained only at the highest temperatures investigated (>1100°C) and powders prepared at lower temperatures frequently contained crystalline Fe2O3. The as-prepared particles were unagglomerated, polycrystalline, and hollow at lower temperatures, but densified in the gas phase at higher temperatures to give solid particles. The strontium ferrite (SrFe12O19) system was studied in detail as a representative example of the Sr-Fe-O system. At temperatures of 1200°C, dense, phase-pure magnetoplumbite-structure material, SrFe12O19, was obtained, while at lower temperatures, small amounts of Fe2O3 were observed. The particles prepared at 800° and 1100°C were 0.1-1.0 μm in diameter, and consisted of crystallites

Phase relations in the system La-Rh-O at 1223 K have been determined by examination of equilibrated samples by optical and scanning electron microscopy, powder X-ray diffraction (XRD), and energy-dispersive analysis of X-rays (EDAX). Only one ternary oxide, LaRhO3, with distorted orthorhombic perovskite structure (Pbnm, a = 0.5525, b= 0.5680, and c= 0.7901 nm) was identified. The alloys and intermetallics along the La-Rh binary are in equilibrium with La2O3. The thermodynamic properties of LaRhO3 were determined in the temperature range 890 to 1310 K, using a solid-state cell incorporating yttria-stabilized zirconia as the electrolyte. A new four-compartment design of the emf cell was used to enhance the accuracy of measurement. For the reaction The compound decomposes on heating to a mixture of La2O3, Rh and O2. The calculated decomposition temperatures are 1843 (± 5) K in pure O2 and 1728 (± 5) K in air at a pressure of 1.01 × 105 Pa. The phase diagrams for the system La-Rh-O at different partial pressures of oxygen are calculated from the thermodynamic information.

Polycrystalline, transparent YAG (Y{sub 3}Al{sub 5}O{sub 12}) ceramics were fabricated by a solid-state reaction method using high-purity Al{sub 2}O{sub 3} and Y{sub 2}O{sub 3} powders. The mixed powder compacts were sintered at 1,600 to 1,850 C for 5 h under vacuum. Optical transmittance in the region between the ultraviolet and infrared wavelengths for YAG ceramics (1 mm thick) sintered at 1,800 C was similar to that for a YAG single crystal.

Homogeneous metastable tetragonal (t′) solid solutions of ZrO2—x mol% CeO2 (x= 20 and 50) were successfully synthesized by the organic polymerized complex method. The citric acid-ethylene glycol solution containing Zr and Ce ions was polymerized at about 140°C and then heat-treated at about 350°C to obtain a precursor. The black precursor was heated at 450°C and then fired up to 1300° or 1590°C, resulting in the homogeneous solid solutions.

The melting behaviors of selected compositions in the system–Si3N4-Y3Al5O12–Y2Si2O7 were determined under 1 MPa of nitrogen. The behavior phase diagrams of the ternary and their binary systems are presented. The ternary eutectic composition contains 10 wt% Si3N4, 27 wt% Y3Al5O12, and 63 wt% Y2Si2O7 with a eutectic temperature of 1430°C. The binary eutectic compositions and temperatures are 25 wt% Si3N4 and 75 wt% Y3Al5O12 at 1650°C, 10 wt% Si3N4 and 90 wt% Y2Si2O7 at 1570°C, and 35 wt% Y3Al5O12 and 65 wt% Y2Si2O7 at l520°C.

Interactions between BaTiO3, and three binary glasses were studied through the reaction of BaTiO3, powder with glass powder. For PbO–B2O3 and PbO–SiO2 glasses, the reaction led to stable compound formation, the substitution of Pb in the BaTiO3 structure, and noticeable grain growth of BaTiO3. The interaction phenomena for these two glass systems were very similar. The substitution of Pb into BaTiO3 is assisted by chemical reactions in which BaB2O4 or Ba2SiO4 is formed. The substitution into BaTiO3 also seems to be closely related to the grain growth of BaTiO3. On the other hand, only compound formation was observed during the processing of BaTiO3 with Bi2O3–B2O3 glass. Neither BaTiO3 grain growth nor Bi substitution took place with the Bi2O3–B2O3 glass system. Based on the observed reactions and the glass viscosity, several sintering aids for BaTiO3 ceramic products are suggested in this paper.

Phase equilibria in the CaO─CuO─Cu system were determined at 1173 K from the results of X-ray diffraction measurements using specimens annealed in the oxygen partial pressure range from PO2= 1 to 10−8 atm. Electromotive force (emf) measurements using ZrO2 solid electrolyte cells were carried out in the ternary phase equilibria. Gibbs free energies for the chemical reactions were summarized by equations with linear temperature dependence, and the standard free energy of formation for Ca2CuO3 was derived. The stability conditions of the oxides are displayed in the p–T–x diagram, and the possible phase equilibria with the liquid are evaluated.

The phase relations in the system Cu-Ho-O have been determined at 1300 K using X-ray diffraction, optical microscopy, and electron microprobe analysis of samples equilibrated in evacuated quartz ampules and in pure oxygen. Only one ternary compound, Cu2Ho2O5, was found to be stable. The Gibbs free energy of formation of this compound has been measured using the solid-state cell Pt,Cu2O + Cu2Ho2O5 + Ho2O3/(Y2O3)ZrO2/CuO + Cu2O,Pt in the temperature range of 973 to 1350 K. For the formation of Cu2Ho2O5 from its binary component oxides, 2CuO(s) + Ho2O3(S) --> Cu2Ho2O5(s) DELTAG-degrees = 11190 - 13.8T(+/- 120) J-mol-1 Since the formation is endothermic, CU2Ho2O5 becomes thermodynamically unstable with respect to CuO and Ho2O3 below 810 K. When the oxygen partial pressure over Cu2Ho2O5 is lowered, it decomposes according to the reaction 2Cu2Ho2O5(s) --> 2Ho2O3(s) + 2Cu2O(S) + O2(g) for which the equilibrium oxygen potential is given by DELTAmu(O2) = - 238510 + 160.2T(+/- 450) J.mol-1 The decomposition temperature at an oxygen partial pressure of 1.52 x 10(4) Pa was measured using a combined DTA-TGA apparatus. Based on these results, an oxygen potential diagram for the system Cu-Ho-O at 1300 K is presented.

An alkoxide-hydroxide route has been developed to prepare Li{sub 4 + x}Al{sub 4 {minus} 3x}Si{sub 2x}O{sub 8} (0 {

Perovskite-type lanthanum iron oxide (LaFeO3) powders were synthesized by glycothermal reaction at 300°C of a precursor that had been previously prepared by solvothermal decomposition of a mixture of lanthanum(III) isopropoxide and iron(III) butoxide (or methoxide) in toluene. Direct glycothermal reaction of the mixture yielded no double oxide, indicating that preparation of the precursor was important for crystallization of LaFeO3 by the glycothermal method.

Spherical lanthanum aluminate powders approximately [mu]m in diameter were produced using spray pyrolysis techniques. These materials were characterized by Z-ray diffractometry and scanning electron microscopy. Two intermediate products were produced and identified as lanthanum oxide and aluminum oxide. These intermediates were present in varying amounts in all of the aerosol-furnace-prepared materials and reflect the short residence time of the aerosols in the furnace. Samples of each aerosol-furnace preparation were further annealed in air for 1 h at 1100 C, and all of them converted completely to lanthanum aluminate.

The effects of Cr2O3 doping (0 to 0.6 wt%) on the microstructure and electrical properties of ternary Pb0.97Sr0.03- [Zr0.458Ti0.452 (Mn1/3Nb2/3) 0.09]O3 piezoelectric ceramics have been studied. Abnormal grain growth (grain sizes of 2.8 to 28.5 μm) and densification (porosities of 2% to 12%) are found, and the tetragonality c/a nearly keeps constant wherease c and a slightly decrease in the doping range. The results for the temperature dependence of electric conductivity and the dielectric constant show that electric conductivity increase continuously over 0.1 wt% content, activation energies are all close to 0.92 eV in the paraelectric state, and the Curie temperature Tc decreases with increasing doping content. Minor additives of ≤0.1 wt% improve the dielectric and piezoelectric properties, but with more additives of ≥0.4 wt% electrical properties appear to deteriorate. Thus, these phenomena can be ascribed mainly to anomalous developed microstructure.

Different ternary carbide phases, namely Ti3AlC2, Ti3AlC, and Ti2AlC, were successfully synthesized in a self-sustaining regime. Direct reactions among elemental powders of titanium, aluminum, and carbon are strongly exothermic, and the resulting reaction products consist of binary carbides and they are partially molten. The use of TiAl, instead of elemental titanium and aluminum, significantly reduces the combustion temperature. As a result, ternary titanium aluminum carbide phases are formed. In addition, the combustion-synthesized products are not sintered and easy to deagglomerate. Reaction conditions and X-ray diffraction patterns of different ternary phases formed in a self-sustaining regime are presented.

Spinel LiMn2O4 as a cathode material for lithium secondary batteries has been synthesized by a mechanochemical process, and its electrochemical properties have been characterized. Highly disordered nanocrystalline LiMn2O4 powders have been prepared by the mechanochemical processing of Li2O and MnO2 powder mixtures for 24 h. Electrochemical characterization of mechanochemically processed powder has shown that the intercalation of Li+ takes place with an initial capacity of 167 mA·h/g in the 2.5–4.3 V range and has better capacity retention as compared to the well-ordered crystalline LiMn2O4 powders. The better capacity retention of the mechanochemically processed LiMn2O4 powder may be attributed to the highly disordered structure that could accommodate the Jahn–Teller distortion of the spinel structure during Li+ intercalation around the 3 V region.

Phase equilibria of the MnO-SiO 2 -MnS system in the temperature range of 1185°-1400°C and the MnS solubility in the MnO-SiO 2 -Al 2 O 3 -MHS system at 1200°C under low oxygen partial pressure have been experimentally investigated using equilibration/quenching technique followed by electron probe X-ray microanalysis and X-ray diffraction analysis. Based on the experimental results, polythermal projection of the MnO-SiO 2 -MnS system was estimated. The system has two ternary eutectic points; namely, one at 1173°±3°C where phases of MnS, MnO, "A" (67.0 mass% MnO-23.6 mass% SiO 2 -9.4 mass% MnS), and liquid coexist, and the other at 1187 ±3 3°C where phases of MnS, Mn 2 Si0 4 , MnSi0 3 , and liquid coexist. All invariant reactions observed above were discussed. The ternary compound "B" containing 74.4 mass% MnO-22.0 mass% SiO 2 -3.6 mass% MnS was observed at 1300°C. In the MnO-Si 2- Al 2 O 3 MnS system, the MnS solubility is strongly affected by Al 2 O 3 content and also the MnO/SiO 2 ratio. The solubility increased as MnO/ SiO 2 ratio increased at a constant Al 2 O 3 content and decreased as Al 2 O 3 content increased at a constant MnO/SiO 2 ratio. In addition, depending on the Al 2 O 3 content and MnO/SiO 2 ratio, the liquid phase is possibly saturated with not only MnS but also other solid oxide phases. In view of inclusion utilization for free-cutting steel, it might have an advantage to decrease the Al 2 O 3 content and increase the MnO/SiO 2 ratio.

An improved coprecipitation method for incorporating three different cations quantitatively in a precursor was developed to prepare a single-phase powder of a ternary compound in the system BaO—La2O3—TiO2. The preparation technique consisted of a preliminary introduction of a specified single component as a preformed binary compound powder. This was followed by the quantitative deposition of the remaining unlike cations as coprecipitated particles in a solution containing a suspension of the preformed compound powder. X-ray fluorescence and electron microprobe analyses showed that the stoichiometric incorporation of the constituent cations was completed for the powder samples thus prepared. From a detailed examination of the phases produced in the composition-controlled powders, it was evident that a ternary compound having the composition BaO · La2O3· 4TiO2 occurs in the present system, for which the X-ray diffraction data were refined and indexed. In addition, the single-phase 1:1:4 compound was found to be synthesized from different precursors through different formation processes.

To establish the correct composition of a ternary compound having higher TiO2 content in the BaO—Nd2O3—TiO2 system, the phase change of samples with variable controlled compositions, which were prepared by a modified coprecipitation method, was examined by X-ray diffractometry and Raman spectroscopy. Identification of the phases present in the calcined samples and microstructural evidence for the fired product from electron microprobe analysis clearly indicated that the ternary compound having the composition 1:1:4 occurs in the present system. X-ray powder diffraction data of the isostructural 1:1:4 and 1:1:3 compounds in each identical ternary system (Ln = La, Nd, and Sm) were refined and indexed. Partial subsolidus phase relations consisting of different composition triangles were also proposed for the present ternary systems.

Spherical fine (micrometer and submicrometer in size) homogeneous BaTiO3 powders were synthesized from ethanol: water solutions of BaCl2 and TiCl4 using the spray-pyrolysis technique. Two different atomizers—twin-fluid and ultrasonic, with a resonant frequency of 2.5 × 106 Hz—were used for mist generation. Hollow spherical particles containing a certain amount of unreacted BaCl2 phase and having a mean particle diameter of 2.5 μm were obtained at 1173 K using a twin-fluid atomizing system. Decomposition of precursors and their transition to the cubic BaTiO3 phase occurred, even at 973 K in the case of the ultrasonic atomizing system. For the initial droplet size of 2.2 μm and residence time of ∼60 s, spherical BaTiO3 particles with the mean particle diameter of 0.53 μm were obtained. A BaTiO3 formation mechanism has been proposed as a reaction between TiO2 and BaCl2 rather than a reaction of oxides.

Sintering of Si3N4 powder with the addition of a Y2O3+ Al2O3 mixture or YAlO3 as sintering aids was investigated. Sintering was improved in the case of YAlO3 additive compared to that for the Y2O3+ Al2O3 mixture. An initial delay in densification was most likely caused by heterogeneity of the liquid phase formed in the case of the separate oxide additions at temperatures above 1700°C.

Ternary compounds in the system BaO—TiO2—La2O3 were prepared by the solid-state reaction technique at temperatures between 1300° and 1400°C using precursor oxides as the starting materials. In an alternative processing technique, BaTiO3 was reacted with appropriate proportions of prefabricated lanthanum titanates at 1350°C to obtain the compounds. Two compounds were identified in the TiO2-rich region of the system. The X-ray powder diffraction pattern of a compound with a chemical composition BaLa2Ti3O10 (BaO·La2O3·3TiO2) is indexed on the basis of an orthorhombic unit cell with a= 7.665 × 10−1 nm, b= 28.524 × 10−1 nm, and c= 3.876 × 10−1 nm. The other compound, which has a chemical composition Ba4La8Ti17O50 (BaO·La2O3·4.25TiO2) occurs in a narrow homogeneity range within the system. The X-ray powder diffraction pattern of the compound is indexed on the basis of an orthorhombic unit cell with a= 12.317 × 10−1 nm, b= 22.394 × 10−1 nm, and c= 3.881 × 10−1 nm. Both the compounds are compatible with BaTiO3 and form pseudobinary joins with BaTiO3 in the system BaO—TiO2—La2O3.

The phase relations at a temperature below "subsolidus" in the system Al2O3-B2O3-Nd2O3 are reported. Specimens were prepared from various compositions of Al2O3, B2O3, and Nd2O3 of purity 99.5%, 99.99%, and 99.9%, respectively, and fired at 1100-degrees-C. There are six binary compounds and one ternary compound in this system. The ternary compound, NdAl3(BO3)4 (NAB), has a phase transition at 950-degrees-C +/- 15-degrees-C. The high-temperature form of NAB has a second harmonic generation (SHG) efficiency of KH2PO4 (KDP) of the order of magnitude of the form which has been used as a good self-activated laser material, and the low-temperature form of NAB has no SHG efficiency.

A simple and low-cost technique was developed to produce unique SrWO4 and WO3 hollow spheres. The SrWO4 hollow spheres were prepared via a precipitation reaction between SrCl2 and Na2WO4 in the presence of polymethacrylic acid, and the synthesis of WO3 spheres used the as-prepared SrWO4 hollow spheres as both precursors and templates. After soaking in HNO3 and calcinations, the SrWO4 were completely transformed into WO3 while the hollow structures were perfectly retained. The “polymer-cation template” model was proposed to describe the formation of the SrWO4 hollow spheres. This technique is feasible in fabricating other inorganic hollow-structured materials.

The photochemical properties of TiO2 films supported on BaTiO3 were investigated to test the hypothesis that dipolar fields from a ferroelectric substrate would affect the reactivity of the supported film. Photochemical reaction products were formed on the TiO2 surface in patterns that correspond to the underlying domain structure of BaTiO3. As the film thickness increases from 10 to 100 nm, the titania more effectively screens the ferroelectric field, and the pattern of reaction products is obscured. It is concluded that dipolar fields from the ferroelectric substrate influence charge carrier transport in the film and spatially localize the reaction products.

The new compounds La{sub 4}Al{sub 2}O{sub 9}, Pr{sub 4}Al{sub 2}O{sub 9}, and Tb{sub 4}Al{sub 2}O{sub 9} were identified in the system 2Ln{sub 2}O{sub 3}{center_dot}Al{sub 2}O{sub 3}. X-ray powder diffraction showed that they were isomorphous with the previously characterized Ln{sub 4}Al{sub 2}O{sub 9} (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Y) and Ln{sub 4}Ga{sub 2}O{sub 9} (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd). La{sub 4}Al{sub 2}O{sub 9}: P2{sub 1}/c, a = 7.97 {angstrom}, b = 11.09 {angstrom}, c = 11.41 {angstrom}, {beta} = 108.8{degree}, Z = 4; Pr{sub 4}Al{sub 2}O{sub 9}: P2{sub 1}/c, a = 7.80 {angstrom}, b = 11.03 {angstrom}, c = 11.31 {angstrom}, {beta} = 109.6, Z = 4; and Tb{sub 4}Al{sub 2}O{sub 9}: P2{sub 1}/c, a = 7.40 {angstrom}, b = 10.58 {angstrom}, c = 11.16 {angstrom}, {beta} = 107.2{degree}, Z = 4. The lanthanum and praseodymium compounds were metastable phases in the Ln{sub 4}Al{sub 2}O{sub 9} systems and transformed into LaAlO{sub 3} and La{sub 2}O{sub 3}, and PrAlO{sub 3} and PrO{sub 1.83} upon prolonged heating at 1,200 C, respectively. Ln{sub 4}Al{sub 2}O{sub 9} (Ln = La,Pr) were synthesized by precipitation of Al(OH){sub 4}{sup {minus}} with Ln{sup 3+} (aq) and subsequentmore » heating at 900 C for 10 h. Tb{sub 4}Al{sub 2}O{sub 9} required calcination at 1,200 C for 10 h. The formation of La{sub 4}Al{sub 2}O{sub 9} and Pr{sub 4}Al{sub 2}O{sub 9} was followed by TGA-DSC, which was also used to assess their thermal stability. Several other members of the above family of compounds were similarly synthesized by the new synthesis route. Particularly, for Nd{sub 4}Al{sub 2}O{sub 9} this represented a significantly improved method.« less

Substitution of Y3+ in CaS results in the cubic rock-salt-type solid-solution Ca1−xY2x/3□x/3S, with x 0.37 and where □ denotes cation vacancies that form for charge compensation. The substitution range determined from polycrystalline samples prepared at 1025°C corresponds to a solubility limit of 16 mol% Y2S3 in CaS. Evolution of the unit cell edge with x indicates that the CaS lattice expands about the cation vacancies. Single-crystal X-ray diffraction studies of samples grown from a eutectic CaCl2–KCl flux revealed no indication of superstructure formation, indicating that Ca2+, Y3+, and vacancies are disordered across the cation sites. Thermogravimetric analysis curves for Ca0.7Y0.2S, CaS, and the ternary compound CaY2S4 indicate oxidative stability up to 430°, 410°, and 490°C, respectively.