The SiH_x stretching absorbance region (2300–2000 cm⁻¹) of seven different commercial Si₃N₄ powders was investigated by diffused reflectance infrared Fourier transform (DRIFT) spectroscopy. The powders evaluated were produced by three different methods: diimide precipitation, carbothermal reduction and nitridation of silicon using different nitriding media and final treatments. SiH groups were detected in all powders. The results show the presence of H-SiXYZ tetrahedral units. XYZ can be different atoms or groups (Si, H, N, O, NH, NH₂ or OH) that bond to the same silicon atom. The H–Si bands were classified considering the backboned atoms of the H–Si into four main tetrahedral by fixing the XY atoms and several possibilities for Z as follows: silicon-based; H-SiSiSi (Z=Si, NH, H or O), nitride-based; H-SiSiN (Z=NH₂ or O), oxynitride-based; H-SiNO (Z=N, NH or NH₂) and silica-based; H-SiOO (Z=NH₂, OH, O or H) tetrahedral configurations. The proportions of these tetrahedral units are different for each powder. The powder produced by the carbothermal reduction process using N₂ as nitriding media presents the largest fraction of H–Si groups linked to silica-based tetrahedral units. For the other six powders the largest fraction of H–Si groups is linked to silicon-based tetrahedral units.

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The process of formation of fluoridated hydroxyapatite, [Ca₁₀(PO₄)₆(OH)_2−2xF_2x] (FHAp) through the hydrolysis of α- or β-tricalcium bis (orthophosphate), [Ca₃(PO₄)₂] (α- or β-TCP) in the presence of fluoride ions (F⁻) was examined. The presence of F⁻ ions improved the hydrolysis of both TCPs. The quantity of F⁻ ions incorporated into the apatite increased with the molar ratio (R) of ammonium fluoride to TCP (R=NH₄F/TCP). When R=0.7, the molar ratio of Ca/P in the products, which contained small amount of CO₃²⁻ ion, was 1.68. On the other hand, for R=0.18 or 0.35, the Ca/P ratio decreased to 1.61–1.64. This phenomenon indicates the formation of Ca-deficient FHAps containing HPO₄²⁻ (and CO₃²⁻) ions. FHAp formed from α-TCP contained fine particles with a size smaller than 0.5 μm, and needle-like crystals whose width depended on the value of R. FHAp formed from β-TCP was needle-like for R=0.18, and spindle-like for R=0.70. Differences in the hydrolysis process between α-TCP and β-TCP were observed. α-TCP is attacked by OH⁻ and F⁻ ions which compete in the formation of FHAp crystals on the surface of the α-TCP particles. On the other hand, β-TCP is attacked by F⁻ ions and forms clusters, and then some of the F⁻ ions that are incorporated in the clusters are liberated, depending on the F⁻ ion concentration in the solution. The clusters loosing F⁻ ions incorporate OH⁻ ions to form FHAp. The F⁻ ions liberated from the clusters then again attack the residual β-TCP . When R=0.18, at an early stage, FHAp with a composition close to fluorapatite [Ca₁₀(PO₄)₆F₂] (FAp) was formed. Then, following the reduction of the F⁻ ion concentration in the reaction media, FHAp with a composition close to hydroxyapatite, [Ca₁₀(PO₄)₆(OH)₂] (HAp), was formed.

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A new method for designing nanomodified inorganic–organic materials is proposed, and one example of synthesizing mesostructured vanadate–poly(ethylene glycol) composite is demonstrated. Commercially available poly(ethylene glycol) was changed in its terminal hydroxy group(s) to ammonium head group by two-step sequential tosylation/nucleophilic substitution in order to enable connection with the vanadate framework component. Self-organization of vanadate and the new organic template was successfully processed in the aqueous mixture to precipitate as a composite by adding sodium chloride. We discuss not only the design of a mesostructured material, but also the reasonable treatment for obtaining it from the mixture by the same technique as the volume shrinkage of an amphiphilic block copolymer in water.

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Three different microstructures in SiC–TiC composites containing Al₂O₃ and Y₂O₃ as sintering additives were prepared by hot-pressing and subsequent annealing. To investigate the dominant toughening mechanism operating in toughened SiC–TiC composites, the microstructure-crack interaction was examined by image analysis. Crack deflection by elongated α-SiC grains was most frequently observed (61% of the observed sites) as the dominant toughening mechanism in the SiC–TiC composites. Crack deflection was generally observed for elongated α-SiC grains with aspect ratio (AR)>2.5 and grain thickness (t)<2.5 μm. Crack bridging (21% of the observed sites) was also observed as one of the operating toughening mechanisms. The rest (18%) of the observed grains fractured transgranularly. The crack bridging mechanism was mostly related to thinner grains with thickness t<2 μm, while transgranularly fractured elongated-grains were mostly related to thicker grains with thickness 2<t<4 μm.

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A 30 vol% aqueous suspension of SiC/Al₂O₃/Y₂O₃ (1/0.02/0.016 volume ratio) system was consolidated by filtration through gypsum mold. The green compact was hot-pressed at 1700–1900°C under a pressure of 39 MPa in an Ar atmosphere. The sintering mechanisms were discussed based on the analysis of shrinkage curves of SiC/Al₂O₃/Y₂O₃ compacts during hot-pressing. The hot-pressing at 1800–1900°C gave dense SiC ceramics (>99% theoretical density) with average four-point flexural strengths of 554–658 MPa, fracture toughness of 4.2–5.3 MPa·m^1⁄2 and Vickers hardness of 20–25 GPa. The Weibull modulus of the SiC hot-pressed at 1800°C was in the range from 4.6 to 7.0. The processing in the heterocoagulation region (pH 5.0) for the SiC and sintering additives gave the highest mechanical properties after the hot-pressing.

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Monazite(LaPO₄)-coated alumina-fiber/alumina-matrix composites were fabricated by hot-pressing, and effects of sintering temperature, sintering time, applied load and fiber volume fraction on mechanical properties of composites were examined. Better fiber debonding of coated fiber than that of non-coated fiber in the composites was observed. All composites using coated fibers showed non-catastrophic failure when hot-pressed under 40 MPa for 1 h below 1250°C, but failure behavior of the composite changed into completely brittle over this temperature. Higher sintering temperature, pressure and longer sintering time corresponded to higher bulk density as well as higher fracture strength, while pseudo-ductility of the composites was reduced with increasing sintering temperature. Increase of hot-pressing pressure and time did not cause a significant ductility reduction of the composites except for increase in bonding of fiber-cloths with matrix sheets. Maximum fracture strength, bulk density and pseudo-ductility of the composites obviously increased with increasing fiber volume fraction under the present hot-pressing condition.

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The effect of coarser grains in AlN raw material on the inhomogeneous structure in AlN sintered body was investigated. It was confirmed that the fine and homogeneous AlN raw material showed higher densification rate at lower temperature, namely, a high sinterability. On the other hand, the addition of coarser grains to the fine and homogenous raw material restricted densification to bring about lower density. As a result of measurement of local porosity and pore size distribution, it was observed that large pores were unevenly distributed near coarser grains. The reason why large pores were left near coarser grains seems to be that not only the coarser grain disturbed shrinkage but also that oxygen, essential for densification of AlN, was insufficient near the coarser grains.

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Ferroelectric random access memory (FeRAM) is expected to be the next generation memory. PbZr_xTi_1−xO₃ (PZT) is considered as a candidate because of its high remanent polarization (P_r). We investigated the relation between physical properties, crystal structure and ferroelectric performance of the sample before and after various heat treatments. From the results, remanent polarization (P_r) and coercive field (E_c) increased with increasing P_O2 during heat treatment. The remanent polarization (P_r) and coercive field (E_c) decreased with increasing Zr content x. Furthermore, the dielectric constants at room temperature increased with increasing Zr content x. On the other hand, Curie Temperature (T_C) increased with decreasing Zr content x or increasing P_O2 during heat treatment. From the structural analysis, the bond length of M(Zr,Ti)-O1 decreased with increasing P_O2 during heat treatment or with decreasing Zr content x of pre-heated samples. Consequently, the ferroelectric performance was affected by changing the defect of oxygen and the strain of the structure.

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Surface energies of α-Al₂O₃ were calculated using molecular dynamics (MD) method. It was found that the surface energy strongly depends on crystal orientation. The surface energy of {10·0} plane had the maximum value of about 13 J·m⁻², while that of the other crystallographic planes ranged between 2 and 4 J·m⁻². The fracture toughness of single crystal α-Al₂O₃ had relatively good correlation with surface energies of {10·0} and {10·2} planes. It was concluded that surface energies highly contributed to the cleavage fracture of {10·0} and {10·2} planes.

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Ab initio band-structure calculations using density-functional theory within the generalized gradient approximation have been performed on α-PbO. The structure optimization of the ground state of α-PbO showed that the calculated lattice parameters and the fractional coordinate of Pb(z) are in good agreement with those of experiments. Partial covalent bonding caused by hybridization of crystal orbitals was seen in the charge density map between Pb and O in the a–a plane. The analysis through an energy diagram of band structures clearly showed that the hybridization of Pb 6s (6p) and O 2p as well as Pb 6s–Pb 6s interaction is the origin of the structure distortion in α-PbO.

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Hydroxyapatite (HAp) becomes colored after heat treatment; however, the cause of this phenomenon is still unclear. The purpose of this study is to investigate the HAp synthesis conditions under which this phenomenon occurs. In the experiments, color was measured using a color meter and the colored HAp was identified by X-ray diffraction (XRD) analysis. The results show that HAp synthesized by wet process has two colors: red and reddish-brown. In the case of the red HAp, the concentration of red components varied from low to high. On the other hand, for the reddish-brown HAp, the concentration of reddish-brown components was almost constant. The red HAp was observed only when tricalcium phosphate (TCP) was not detected by XRD analysis and SEM.

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Second-order optical nonlinearities for the langasite-type phases obtained by crystallization of corresponding glasses are clarified for the first time. It is confirmed that most of langasite-type crystalline phases can be formed by crystallization in the corresponding glasses without introducting of any impurity phases, e.g., the glasses with the stoichiometric composition of Ba₃Ga₂Ge₄O₁₄, BaGa₄La₂Ge₂O₁₄, Pb₃Ga₂Ge₄O₁₄, etc. We find that Pb₃Ga₂Ge₄O₁₄ and Pb₃AlGaGe₄O₁₄ phases exhibited strong second-harmonic intensities of approximately 100 times as large as α-quartz by means of a powder technique, demonstrating that those langasite-type crystals are excellent nonlinear optical materials. It is also suggested that the octahedral site is one of keys for second-order optical nonlinearity in langasite-type crystals.

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