The Rietveld refinements of crystal structure were undertaken on powder samples of ZrO₂ and HfO₂ quenched from 600°C⋅6GPa. The results on orthorhombic ZrO₂ were consistent with those of a single crystal obtained under pressure. The compressibility of this phase was calculated as 4.65×10^-3GPa^-1. The results on HfO₂ were also conformable to those on ZrO₂.

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As a new preparation method of transparent conductive oxide films, plasma oxidation of metallic tin films has been investigated. Although the oxidation did not take place in the absence of nitrogen trifluoride, the addition of nitrogen trigfluoride was found to convert evaporated tin films to hazy transparent films at a low temparature of 125°C. The as-reacted films have low conductivities (about 10^-8S·cm^-1), mainly because they contain too much fluorine. However, the annealing of the films in air at temperatures higher than 400°C reduced the fluorine contents to several atomic per cents wite respect to tin and the conductivities of the films increased up to 10S·cm^-1.

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The erosive wear of four kinds of brittle materials, Si₃N₄, PSZ, SiC and Glass, was tested using eight kinds of impingement particles having different hardness. The erosion rate depended remarkably on the ratio of the hardness of an impingement particle (H_p) to that of a target (H_t). When H_p/H_t>>1, severe erosive wear was observed in all target materials. When H_p/H_t<1 and the fracture toughness of target materials (K_ct) was small, that is the case with SiC and glass as target materials, significant erosive wear was observed. However, when H_p/H_t<1 and K_ct was rather large, that is the case with Si₃N₄ and PSZ as target materials, almost no erosive wear was observed. The interaction with material properties of target and impingement particle on the erosive wear mechanism is discussed, and a map of erosive wear relating H_p, H_t, K_ct and K_cp (fracture toughness of impingement particle) is proposed.

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Submicron grinding of BaTiO₃ powder was studied with a vibration ball mill using alumina balls from 30mm to 1mm in diameter. BaTiO₃ clinker obtained by calcining of an equimolar mixture of BaCO₃ and TiO₂ was preground to 1.95μm. The average particle size was calculated from specific surface area measured by BET method. The results obtained are summarized as follows;
(1) Submicron grinding of BaTiO₃ powder was possible with small balls in short time on the factory base.
(2) With balls of 1mm in diameter, the minimum specific surface area diameter (D_s) was 0.026μm in one milling operation.
(3) The following empirical relation was obtained, log(SS)=-0.588logr+1/2logt+0.701 where SS is, specific surface area, r is ball radius and t is time.

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The synthesis of a material having low thermal expansion coefficient and high electrical conductivity in the system Nb₂O₅-TiO₂ was investigated. The average thermal expansion coefficient of Nb₂TiO₇ and Nb₁₀Ti₂O₂₉ unit cells was 2.9×10^-6/°C and 2.8×10^-6/°C, respectively. Sintering of Nb₂TiO₇ was promoted by suitable calcination and by adding a metal oxide such as SrO and PbO. The high-strength and low thermal expansion polycrystalline ceramics were obtained by controlling grain growth. Addition of a metal oxide such as SrO promoted the sintering of Nb₁₀Ti₂O₂₉. These polycrystalline ceramics showed low thermal expansions due to microcracking. Relatively high electrical conductivity was attained by reducing these sintered ceramics.

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Mixtures of SiO₂ and Al₂O₃⋅2H₂O with the atomic ratio Si/Al=1 were reduced by the stoichiometric amount of carbon between 1350° and 1500°C in flowing nitrogen to prepare sialon powder. The nitrogen content in the prepared powder, predominantly β-sialon, leveled off after heating for 5-15h at each temperature. However, loss of Si increased with increasing temperature. The decomposition of the sialon powder was observed at 1500°C. The morphology of the sialon particles prepared at 1350°C was similar to that of the starting mixtures of SiO₂ and Al₂O₃⋅2H₂O. The sialon particles prepared at 1470°C were finer than those at 1350°C and different in morphology from the starting powder.

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The corrosion behavior of MgO-ZrO₂ and Ca O-ZrO₂ sintered bodies was studied in molten fluoride and fluorosilicate salts. Most samples used for a corrosion test were commercially available cubic stabilized zirconia (CSZ) and specimens made in our laboratory. The CSZ containing MgO and CaO readily corroded in molten fluoride salts. However, the sintered body of ZrO₂ containing Y₂O₃ was superior to other ZrO₂ ceramics in regard to the corrosion resistance. The corrosion depth of Mg-CSZ, Ca-CSZ and 3 Y-PSZ depended on the ionic radius of alkaline metal cations of the fluoride salts. The phase transformation of various CSZ ceramics from cubic to monoclinic phase, which occurred on the corrosion site, was considered to be caused by dissolution (or elution) of the stabilizer from the sintered body to the salt. The corrosion of CSZ in hexafluorosilicate salt was estimated to be caused by decomposition of a fraction of the fluorosilicate salt to fluoride and silicon fluoride. The corrosion depth in hexafluorosilicate salt was smaller than that caused by the fluoride salt in CaO-ZrO₂ and MgO-ZrO₂ sintered bodies in contrast to the Y₂O₃-ZrO₂ sintered body. The magnitude of the phase transformation of CSZ depended upon the kind of stabilizer and the grain size of the cubic phase.

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This study was concerned with the formation of spinel solid solutions and color development in the system Li₂O-MO-3TiO₂ (M=Mg, Co, Ni). Specimens were prepared by calcining mixtures of oxides of cobalt and titanium, and carbonates of lithium, magnesium and nickel at 1000°C for 2h. The formation range of spinel solid solutions was examined by X-ray analysis, and the lattice parameter of each solid solution was calculated. The structures of Li₂O-MgO-3TiO₂ and Li₂O-CoO-3TiO₂ solid solutions were refined by the pattern fitting method for powder X-ray diffraction. The color was discussed by measuring the spectral reflectance. The results were summarized as follows;
1) In the system Li₂O-(1-x)MgO-xCoO-3TiO₂, a spinel solid solution with super structure was observed in the range of 0<x<1.
2) In Li₂O-(1-x)MgO-xNiO-3TiO₂ and Li₂O-(1-x)CoO-xNiO-3TiO₂ systems, a spinel solid solution with super structure was obtained in the range of 0<x<0.6. When x=0.8 and x=1.0, the formation of spinels was not observed.
3) According to the results of structure refinement [cubic, S. G.=P4₃32, Z=4, a=8.377 (M=Mg), 8.373 (M=Co) Å], the cation distribution of Li₂O-MO-3TiO₂ (M=Mg, Co) is nearly Li_0.5M_0.5 [Li_0.5Ti_1.5]O₄ (M=Mg, Co). Li⁺ and Ti⁴⁺ in octahedral sites have the 1:3 order. Between the separations of Li⁺-O^2- and Ti⁴⁺-O^2- in octahedral sites, a fairly large difference was noted, As Ni²⁺ revealed strong octahedral site preference, an increase in Ni²⁺ caused the migration of Li⁺ from octahedral to tetrahedral sites in Li₂O-(Mg, Co, Ni)O-3TiO₂ system. Consequently, the intensity of superlattice lines of spinel decreased as the amount of Ni²⁺ increased.
4) The color of spinels changed from white to turquoise in Li₂O-(1-x)MgO-xCoO-3TiO₂ system, from white through light yellow to yellow in Li₂O-(1-x)MgO-xNiO-3TiO₂ system, and from turquoise through green to yellow in Li₂O-(1-x)CoO-xNiO-3TiO₂ system.

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Programs for finding the unit-cell constants and the possible space groups of cubic, tetragonal and hexagonal substances from X-ray powder diffraction data are written in N₈₈-BASIC. The method of programs for tetragonal and hexagonal cases is based on an idea that at least one reflection with index h00, hh0 or 00l may exist in the observed diffraction lines. Trial unit-cell parameters a, for example, are then obtained by assuming that all the observed reflections have indices h00 or hh0. The c parameters for a particular a parameter can then be derived by assuming that the observed reflections have indices h0l, hhl or 00l. For each set of the a and c parameters thus obtained, 2θ_cal are calculated for various indices hkl and compared with 2θ_obs. Then, If all of 2θ_obs are explained in terms of 2θ_cal within given window widths (±Δ2θ), the a and c parameters are saved as a possible set of unit-cell constants. After the above calculation, the systematic extinctions of reflections for all space groups belonging to tetragonal or hexagonal systems are examined, and the unit-cell constants with possible space groups giving high values of reliability indices R are selected. In cubic system, somewhat different algorithm is used for finding the unit-cell constant. The reliability index R used in our program is given by R=(Number of all observed reflections)/(Number of all reflections calculated for a given space group), where the reflections are those giving different d-values.

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For the application to first wall materials of fusion reactor, irradiation damages of Si₃N₄-SiC amorphous films that were prepared by plasma CVD method have been investigated experimentally by use of an intense pulsed light-ion beam. The ionbeam irradiation was carried out by using a magnetically insulated diode of flat-type, where an external transverse magnetic field was applied to insulate the motion of electrons. The inductively calibrated diode voltage was being kept constant at 650kV, and the dose rate of the beam was 10¹³ ions cm^-2 shot^-1 (H⁺ ion). The content of the H⁺ ion found to be more than 80%, and the remainder consisted of C⁺, C²⁺, C³⁺ and H₂⁺ ions. From the changes of surface texture, film thickness, composition, and cross-sectional views, we evaluated these irradiation damages. Blistering for SiN_1⋅42(-Si₃N₄) film, flaking for SiC_1⋅04(-SiC) film and the intermediate texture between blistering and flaking for SiN_0⋅65C_0⋅62 film were observed after the irradiation, A ccording to the observation of cross section of the films, the irradiation damage was limited in the surface layer, and peeling off of the whole film from the substrate (316 stainless steel) did not occur. Erosion rate (the decrease in film thickness per one shot of irradiation) was in the range from 0.46 to 0.73μm shot^-1, where the SiN_1⋅42 film showed the smallest rate. N and C contents in the films were found to have decreased, and Si content was found to have increased by EPMA measurements.

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Sintering of TiSe₂ was investigated by hot-pressing at 800°-1550°C in an argon atmosphere. During firing, some Se atoms were released resulting in larger non-stoichiometry of TiSe₂. In order to investigate non-stoichiometry and change of crystal structure, non-stoichiometric compounds were synthesized in the range of Se/Ti ratio 1.4-2.2. It was shown that TiSe₂ had a wide non-stoichiometric region with CdI₂-like structure in the range of Se/Ti ratio 1.4-2.0. Different trends in the C-axis variation of non-stoichiometrie compounds were found between the ranges of Se/Ti ratio 1.4-1.6 and 1.6-2.0. Similar phenomena were observed in the non-stoichiometric compounds of fired specimens. Distinct correspondence betwem the lattice parameters of fired specimens and those of synthesized non-stoichiometric compounds was observed. Comparison of the lattice parameters revealed that the degree of non-stoichiometry of fired specimens could be estimated from synthesized compounds. Sintering process was always accompanied with release of Se and progressive increase of non-stoichiometry. The fact suggested that the process was controlled by diffusion of Ti and Se atoms through vacancies.

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β-sialon was fabricated from α-Si₃N₄ and aluminum-iso-propoxide by hot-pressing. Bending specimens of hot-pressed β-sialon were heat treated at 800° to 1400°C for 0.5 to 10h in air, and effect of heat treatment on the bending strength was examined. Free and fractured surfaces were observed by optical and scanning electron microscope after heat treatment under different temperature-time conditions. The strength, when heat treated for 2h, increased with increase in the heat treating temperature and showed the maximum value of 150kg/mm² at 1200°C. But the strength decreased a little at 1400°C. The strength did not decreased with heat treating time up to 10h at 1200°C. Most of the specimens fractured from surface flaw generated by grinding. The observed increase in strength by heat treatment at 800° and 1000°C was ascribed to the blunting of crack tips, and that at 1200°C was to the blunting of crack tips and also to the coating of surface flaws with oxide layer.

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In order to in vestigate the effect of grain boundary structure on the high-temperature strength of SiC, three kinds of SiC materials were prepared by pressureless sintering; material A with sintering aids of B+C, material B with B+C+AlN, and material C without any sintering aid. Their strength was measured by three-point bending at temperatures from room temperature to 2070K. The grain boundary structure was observed by HR-TEM. The following results were obtained.
(1) The strength of material A increases with increasing temperature up to 2070K. The fracture mode is transgranular at all temperatures studied. At the grain boundaries observed, a non-crystalline phase of 2-5nm in thickness is always found. This phase is thought to be either a compound of B and C or an extended grain boundary.
(2) The strength of material B increases up to 1770K, but above that temperature it decreases rapidly. The fracture mode also changes at that temperature from transgranular to intergranular. There exists also a 2-5nm thick non-crystalline phase at grain boundaries. The boundary phase is thought to be a compound in the system B-C-AlN. Above 1770K this phase is considered to flow viscously under stress to bring about boundary sliding which causes the strength to decrease.
(3) The strength of material C is almost independent of temperature. There exists again a 3-5nm thick non-crystalline phase at grain boundaries, but the boundary phase is thought to be an extended grain boundary.
(4) The dihedral angles observed in material C are frequently much larger than the critical angle of 60°. This observation is against the Prochazka's thermodynamic limitation, γ_gb/γ_sv<√3. The large dihedral angles may come from the existence of a grain boundary phase, which lowers the boundary energy.
(5) Densification of materials A and B is thought to proceed by the diffusion through the grain boundary phases.

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Oxidation behavior at low temperature of commercial submicron α-, and β-SiC powders with similar specific surface area and their sinterability were studied. These powders were stable in an 8-month-exposure test in water and air at room temperature, and they were not significantly oxidized up to 200°C. All powders, however, were oxidized to the same degree in the temperature range of 200°-300°C, but different behavior was observed above 300°C. Powders which had higher amount of free-silica and free-carbon showed a smaller increase of free-silica by oxidation. Free-silica which was formed by oxidation inhibited sintering of SiC, and the threshold value which was responsible for the densification depended on the fabrication method of powders. The effect of free-silica on the densification was most significant in α-SiC, Plate-like crystals grew with increasing amount of free-silica and the densification was prevented by this growth. Carbon addition prevented the degradation of sintering activity by carbothermic reduction of free-silica.

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Silicon nitride containing various amounts of MgO were hot-pressed at 1800°C and 300kgf/cm² for 60min, and their physical and tribological properties were in vestigated. Nearly full densities were obtained for sintered bodies containing 1-15wt% MgO. The fracture toughness was low and its dispersion was much greater for MgO addition less than 5wt%, as compared with MgO addition more than 5wt%. The Vickers hardness decreased up to 5wt% MgO content, and was almost constant with further addition of MgO. The tribological properties were measured, using a pin-on-disk friction and wear tester. The coefficient of friction was almost constant regardless of MgO addition. On the other hand, the specific wear rate scattered much for MgO addition less than 5wt%, and decreased with MgO content over 5wt%. The negative correlation was recognized between fracture toughness and specific wear rate for specimens less than 5wt% MgO addition, and it is supposed that the wear was caused by brittle fractures at contact points. Above 5wt% MgO addition, on the other hand, the wear is mainly controlled by the amount or some properties of glassy phase, which is formed as a result of excessive MgO addition.

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Local structures around Ag⁺ ions in photochromic glasses in the system AgBr-CsBr-PbBr₂ were investigated by Ag K EXAFS (extended X-ray absorption fine structure) analysis. Using AgBr crystals (Ag-Br=2.88Å) as a reference sample, average Ag-Br distances for 12AgBr⋅13CsBr⋅75PbBr₂ and 22AgBr⋅10CsBr⋅68PbBr₂ glasses were estimated from |F(r)| curves to be 2.81 and 2.88Å, respectively. It was concluded on the basis of the Ag-Br distances that chemical environments of Ag⁺ ions in the glasses are similar to those in AgBr crystals. This similarity probably explains the photochromic property of the glasses.

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Various types of carbon fiber/carbon composites (C/C composite) were prepared. Weight loss and microstructural change of the composites were observed after heat-treatment at 3000°C. The weight loss of the composites with the matrix derived from thermo-setting resin was larger than that of other carbon materials including the composites with the matrix of CVD carbon. At the interfaces between fiber and matrix, carbon matrix was mainly lost by evaporation. This is probably due to the residual stress which activates the matrix carbon near the interface. In the composite with rough columnar matrix, large gaps were observed between fiber and matrix, which were caused from orientation of graphite crystallite in matrix.

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The effect of oxygen partial pressure on the synthesis of a supereonducting perovskite-like phase from a mixture of BaCO₃, Y₂O₃, and CuO was studied. The rate of perovskite formation reaction and critical current density in the superconducting state at 77K increased with increasing oxygen partial pressure.

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