The phase relation of Cr-N system was studied in the temperature 1100∼1500 °C and the partial pressure of nitrogen 0.01-1 atm. The samples which were equilibrated with the atmosphere and quenched, were examined by chemical analysis and X-ray powder diffraction, and the temperature (T)-partial pressure of nitrogen (P_N2) -composition ( x ) diagram was established. Under most of the experimental conditions studied, single phase Cr₂N was stable, but lower Pm, metallic Cr phase appeared. The N/Cr ratio was approximately 0.38 in the Cr₂N phase which coexisted with the metallic phase.
The defect structure of Cr₂N was studied by means of measured density and the lattice parameter of quenched specimen. The dominant defect in Cr₂N was found to be nitrogen vacancies on the nitrogen site, and the metal site was approximately perfect. The Cr₂N phase is consequently expressed as Cr₂N_1-x. The non-stoichiometry found under the present experimental conditions was 0.04<x<0.24. It increased with increasing temperature and with decreasing P_N2.
Vacancy formation mechanism in the Cr₂N phase was analysed with two models. The first is an ideal solution model in which no interaction between defects is assumed, and the second the Bragg-Williams type model which assumes the interaction. The second model agreed better with the T-P-X diagram.

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The phase relations in the stuffed tridymites A²⁺B₂³⁺+O₄(A²⁺;Ca, Sr, Ba, B³⁺;A1, Ga) with different sequences of B³⁺O₄-tetrahedra (Table 1) were studied at 1000∼1500°C in air by X-ray powder diffraction on quenched samples, high-temperature X-ray diffraction and differential thermal analysis (Fig.1, 2 and 5). Two types of solid solutions, CaAl₂O₄-type(UUDUDD+UDUDUD) and BaAl₂O₄-type (UDUDUD), were formed in the wide range of composition in both series of the aluminate and gallate (III) systems. The lattice constants, particularly cspacing in a hexagonal system, and stability ranges for each type structure were closely correlated to the average ionic radius of alkaline-earth metals which were stuffed in the channel made up of B³⁺O₄-tetrahedra (Fig.6), though the ranges of ionic radius for these structures were slightly different between the aluminate and gallate(III) systems. In the aluminate systems, only one phase-transition was found; the BaAl₂O₄-type structure distorted reversibly to the α-SrAl₂O₄-type structure in Sr-rich compositions at low temperatures. In the gallate (III) systems, however, four types of phase transitions were observed; the BaAl₂O₄-type structure in Ba-rich compositions distorted reversibly to the α-BaGa₂O₄-type (Fig.3 and 4). The BaAl₂O₄-type solid solutions containing about equal amount of Ba²⁺ and Sr²⁺ were found to transform to the CaAl₂O₄-type structure, although the transition was very sluggish. The CaAl₂O₄-type solid solutions around the SrGa₂O₄ composition transformed slowly to the ceSrGa₂O₄-ty pe at low temperatures, but in the SrGa₂O₄ composition the single phase of the CaAl₂O₄-type structure was not quenchable. In the binary system CaAl₂O₄-CaGa₂O₄, a wide range of formation of the δ-CaGa₂O₄-type structure (so-called metastable-CaGa₂O₄-type)and the transition to the low-temperature α-form (so-called CaGa₂O₄- I -type) were observed, suggesting stable existence of the δ-CaGa₂O₄-type structure in the stuffed tridymites.

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The stable phase of Mg₂GeO₄ is spinel type (γ-phase) at room temperature and it converts to olivine type (α-phase) at temperature above 810°C and melts at 1855°C in air. In the present study, the phase equilibrium among a-, 7'- and the melt were empirically determined in the region of temperature and pressure up to 2200°C and 5 GPa. The dependency of the melting temperature on the pressu re is linear and given by d Tm/dP =30°C. GPa^-1. The triple point, where α-, γ-phases and the melt coexist, locates at 1950°C and 3.5 GPa. The phase boundary between α-and γ-phases is a curve concave downwards as illustrated in Fig.3.

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The change of the lattice constant of manganese, iron, or cobalt alminate with the spinel structure by the valence and/or the coordination state of the transition metal was investigated. The carbonate or the oxide of manganese, iron, or cobalt and a-alumina was mixed in the equivalent ratio, and the mixture was heat-treated at 1300°C or 1400°C. The oxygen partial pressure (PO₂) of the atmosphere was varied from 2.1 × 10^-1 atm to 4.33 × 10^-12 atm for the heattreatment at 1300°C, and from 2.1 × 10^-1 atm to 3.98 × 10^-11 atm at 1400°C. The crystalline phases of the product were identified by the X-ray powder diffractometry. The results are listed in Table 1. For the spinel phase, the lattice 'constant was determined by the precise measurement. The lattice constant of the spinel phase is shown as a function of Po₂ in Fig.3.
( 1 ) Co-Al-O system: The lattice constant was not changed for all the temperature an d Po₂ The spinel phase was CoALO, and it is supposed that the valence of the cobalt ions w ere kept bivalent. ( 2 ) Fe-Al-O system: The lattice constant was held almost constant in the lower Po₂ region, and increased with the increase of Po₂. The spinel phase was the solid solution of FeAl₂O₄ and Fe₃O₄, i. e. the Fes+ ions were formed in the higher Po₂ region, and substituted for the AP⁺ ions. ( 3 ) Mn-Al-O system: MnAAl₂O₄ was formed. The lattice constant was held almost constant in the lower Po₂ region, and increased with the increase of Po₂. It is supposed that the Mils ions were formed in the higher Po₂ region, and substituted for the AP+ions, similarly to the Fe-Al-O system. There observed a bending of the curve in Fig.3. It would be interpreted as follows; In the lower Po₂ region, the distribution of the spine' phase was normal as the Mn²⁺ ions have the tetrahedral site preference. The increase of Po₂ favored the formation of the Mns³⁺ ions, which prefer the octahedral site. Therefore the spinel was intermediate phase between normal and inverse, and the lattice constant increased abruptly.

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The heats of solution were measured for As-S glasses in aqueous solutions of NaOH, NH₃, (NH₄)₂ S and Na₂S. The anion species formed after the dissolution were identified by TLC and the composition dependence of heats of solution were discussed by assuming the dissolution mechanism.
The enthalpy change in each solution was negative, i. e., exothermic for every glass. The exothermic heat per formula weight of AsSm, in NaOH and NH₃ solutions linearly decreased with an increase of mole fraction of AsS_1.5, in the pseudo-binary system AsS_1.5-AsS_2.5. TLC examinations showed that AsO₃^3- and AsOnS_4-n3- (n=1, 2 or 3) were the anion species formed on dissolution in NaOH solution. The glass of high sulfur content formed anions of low n values and gave higher heat on dissolution. In NH₃ solution, the four-coordinated anions were not formed and the heats were fairly low.
The heats of solution in sulfide solutions did not depend on the galss composition and were nearly equal to the heat of solution of AsS_2.5 glass in NaOH solution. This behavior can be interpreted by assuming that the major species of four-coordinated anion is AsS₄^3- formed by coordination of S^2- which exists in large excess in the sulfide solutions.

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New functional applications of some ferroelastic crystals are expected in the optoelectronics and related fields. Thermal phase transition of ferroelastic Ba₂TiGe₂O₈ has been investigated with polarized microscopy and the X-ray diffraction method at high temperatures. Ba2TiGe208 undergoes phase transtion at about 870°C from the ortho rhombic low-temperature form (mm2) into tetragonal high-temperature form (4mm). At 550°C, stress-strain hysteresis loop was observed and it was confirmed that Ba₂TiGe₂O₈ is a ferroelastic crystal belonging to the species 4 mmFmm 2. The birefringences perpendicular to a, b and c axes of the orthorhombic low-temperature form were measured versus temperature: the crystals become smoothly uniaxial at about 870°C.
The average stru cture of Ba₂TiGe₂O₈ at room temperature was determined to elucidate the mechanism of thermal phase transition and the propagation of the twin planes. The structure is built up of [Ge₂O₇]^6- double groups linked together with TiO₅ square pyramids to give fiat sheets perpendicular to the c-axis. These flat sheets are bonded together by the Ba²⁺ ions. There exist two independent [Ge₂O₇]^6- double groups. The observed electron density distribu-, tion strongly suggests that in a half of [Ge₂O₇]^6- group the bridging Ge-O-Ge bond angles on the (001) projection deviate about 10° from 180°, yielding two possible orientations for these groups. A long period ordering of the orientation of the groups appears to be responsible for the long period superstructure of the low-temperature form.

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The surface state of the cobalt-adsorbed γ-Fe₂O₃ particles and their structural changes caused by heat treatment are studied by chemical analysis and magnetic measurements. As shown in Fig.1, the coercive force of γ-Fe₂O₃ increases with increasing amount of cobalt adsorbed. The increased coercivity decreases to the level of starting γ-Fe₂O₃ by removing the cobalt-absorbed layer in a diluted acid solution (Fig.2).
The distribution of cobalt across the surfa ce layer of a particle is estimated from the results of dissolution experiments (Fig.2), assuming that the number of cations per unit volume of the oxide is approximately equal to 5×10^-2/ų (Fig.3). As shown in Fig.3 and 4, the surface anisotropy, responsible for the increased coercivity of the particles, is in less than 3Å depth from the original particle surface before cobalt adsorption and is strongest at the original interface. The, cobalt concentration in the surface region decreases when the particles are heated to about 650°Cin air. A remarkable decrease in cobalt content was observed in the temperature range between 250°C and 400°C with X-ray photoelectron spectroscopy (Fig.10). The observed decrease in cobalt content is due to the inward diffusion of cobalt, and the surface anisotropy disappears with the formation of a solid solid solution of cobalt iron(III) ferrite.
The cobalt concentration in the surface region, however, increases again above 650°Caccompanied by the precipitation of α-Fe₂O₃. The growth of α-Fe₂O₃ is presumed to begin near the center of a particle because of the lower cobalt content, resulting in the decrease in iron content and the increase in cobalt content in a spinel phase of the inner part of the particle. Consequently, interdiffusion of iron to the inner part and cobalt to the outer part is considered to occur in the particle. Cobalt is finally concentrated to a stoichiometric cobalt ferrite thus showing a maximum peak value of coercivity (Fig.5), and particles are subject to phase separation into α-Fe₂O₃ and CoFe₂O₄.

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The TiO₂-SiO₂ glasses containing TiO₂ up to 15 wt% have been prepared by heating the gels made from the mixed solution of Ti (OC₃H₇)and Si (OC₂H₅)₄. The gels obtained by hydrolyzing the alkoxide solutions at 40°C with the addition of 50 or 100 moles of water for a mole of alkoxides were successfully converted to relatively large TiO₂-SiO₂ bulk glasses by heating to 900°C. The ultra low thermal expansion was attained in such alkoxy-derived TiO₂-SiO₂glasses. The infrared spectra indicated that the structure of the glasses was similar to those prepared by the melting technique. Ti⁴⁺ ions in the glasses are supposed to be tetrahedrally coordinated with oxygen by the analysis of infrared spectra and other properties. The water content of the glasses ranged between 0.1 and 0.2 wt%, which was considerably large compared to conventional glasses. It was found that the amount of water added in the hydrolysis process of alkoxides, temperature of hydrolysis and temperature of heating of the gels affected the water content in the final product and the precipitation of anatase crystal. Precipitation of anatase crystal increased both thermal expansion and density of the glasses.

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The glass-forming region in the Na₂O-Ga₂O₃-SiO₂ system was determined, and the density, Vickers hardness and SiK_β X-ray emission spectra of the glasses obtained in the system were studied.
The glass-forming region in this system was found to be considerably wider than that in Na₂O-Ga₂O₃-SiO₂ system. The maximum Ga₂O₃ content in a glass was 50mol% compared wit h 25 mol% for Al₂O₃. The mean atomic volume and Vickers hardness were found to change abnormally with glass composition. They showed a sudden change at the composition of the Ga/Na ratio 1. This anomaly is similar to that observed in the Na₂O-Ga₂O₃-SiO₂ system.
The correlation curve between SiK_β X-ray emission spectra and the Ga/Na ratio showed the similar anomalous change at the Ga/Na ratio of 1. Both the chemical shift, Δλ, and half width, W, decreased with the addition of Ga₂O₃ to sodium silicate glasses, reached minimum at the Ga/Na ratio of 1 and increased again with further addition of Ga₂O₃. The results seem to indicate that non-bridging oxygens existing in sodium silicate glass change into bonding oxygens with the addition of Ga₂O₃ by forming GaO₄-Na⁺ units.

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Electric conduction in metastable β form of sintered pure Bi₂O₃, has been investigated by measuring the conductivity, the ionic transference number and the Seebeck coefficient.

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To obtain the glass ceramics containing the semiconducting oxide crystals, the crystallization of Nb₂O₅-V₂O₅-P₂O₅ glasses and the electrical conductivity of the glass and glass ceramics have been investigated. The limit composition of glass formation was found near the tie line between 0.9 V₂O₅⋅0.1 P₂O₅ and O.6 Nb₂O₅⋅O.4P₂O₅, which were the glass formation limits of the binary systems. The conductivity increased with the increase of the V₂O₅ content. The conduction mechanism was considered to be the small polaron hopping between V⁴⁺-O-V⁵⁺ pairs as proposed by N. F. Mott. The substitution of Nb₂O₅ for P₂O₅ under the same content of V₂O₅ increased the conductivity. The NbO₆ octahedron connecting V⁴⁺-O-V⁵⁺ pairs in place of PO₄ tetrahedron in the glass structure was considered to facilitate the conduction by such as increasing the mobility of charge carrier. By the heat-treatment for the crystallization of 0.2 Nb₂O₂⋅0.6 V₂O₅⋅2P₂O₅ or 0.4 Nb₂O₅⋅0.4V ₂O₅0.2 P₂O₅ glass the conductivity was increased from about 10^-6to 10^-1 Ω^-1⋅cm^-1 (25°C) and the activation energy for conduction was decreased from 0.5 to 0.1 eV. The crystallization in V₂O₅-13₂O₅ glasses proceeded often from the surface. The addition. of Nb₂O₅ was effective on the nucleation of the homogeneous crystallization and on the development of fine crystals. The pillar-like large crystals were observed on the fractured surface of the glass ceramics containing less amount of V₂O₅ +NW, . It was confirmed by X-ray diffraction and EPMA analysis that one of the crystalline phases was the solid solution of V₂O₅ with Nb₂O₅ (a few mol%), whose conductivity was 10^-1 Ω^-1⋅cm^-1. The conductivity of the glass ceramics, where the grains of this crystal were connected each other, was remarkably high.

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The effect of microstructure of sintered β''-alumina on the ionic conductivity was investigated.β''-alumina powders were prepared by a spray-pyrolysis technique. Atomizing liquids were ethanolic solutions of sodium, magnesium and aluminum nitrates corresponding to Na₂O⋅0.6MgO⋅5Al₂O₃( I ) and Na₂O⋅0.3MgO⋅6Al₂O₃(II). Powders obtained at the highest flam e temperature of 1100°C consisted of spherical hollow particles (1∼20 μ) of r-alumina. The as-produced powders were calcined at 1100°C for 1∼2 h and conver ted into β''-alumina phase. Green compacts were made with an one-direction press and sintered at 1560∼1600°Cfor 5 min to 4 h. The relative densities of the sintered bodies were between 89 and 98% of the theoretical density. Sintering at 1560°C for 4 h or 1590°C for 5 min gave a microstructure consisting of uniform fine grains (1∼3μ) ( I ). However, sintering at 1590°C for 1.5 h gave a duplex structure consisting of coarse (90∼150μ) and fine grains (1∼2μ) ( I ). The increase of sintering temperature or time increased the degree of preferred orientation of (001) plane of β, β''-alumina grains normal to the press direction ( I, II ).
The specific resistivities of the sintered bodies were measure d by using a conventional A. C. bridge circuit in the temperature range between 100°and 350°C. The samples showed the resistivities of 14∼96 Ω⋅cm at 300°C along the press direction ( I, II ). The resistivities of the samples decreased with an increase in density and with a decrease in preferred orientation of (001) plane of β, β''-alumina grains. The activation energies varied between 4 and 10 kcal/mol and were lower for the duplex structures than for the uniform fine-grained microstructures. This indicates that the activation energies depend upon the amount of grain boundary in the sintered body.

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The preparation and the crystal growth of black phosphorus have been studied at high pressures and high temperatures. A wedge-type cubic anvil high pressure apparatus was used in the present experiments. Black phosphorus was prepared from white phosphorus in the ternperature range 200∼500°C at 3.8 GPa and also from red phosphorus above 450°C at high pressures. From the measurement of the electrical resistance the melting points of black phosphorus have determined at high pressures. The melting point increased with increasing pressure. The anomaly in DSC and TGA has been found around 490°C at atmospheric pressure.Black phosphorus did not melt and rapidly decomposed around the temperature. When black phosphorus was melted in the carbon furnace and slowly cooled at high pressures, the large single crystals have often been grown. The size of the largest one was 4 mm in diameter and 5 mm in'length.
Black phosphorus is a layer material. The anisotropy of resistivity in the single crystals has been studied. The resistivities along the a-axis and c-axis were about 0.1 Ω⋅cm and
1 Ω⋅cm, respectively at room temperature. It is interesting to note that the anisotropy in the layer has been observed. The resistivity along the b-axis (perpendicular to the layer) was 10²∼10³Ω⋅cm. The resistivity along the a-axis was insensitive to pressure; on the other han d, the resistivity along the c-axis decreased rapidly with increasing pressure. The values of these resistivities became to be nearly equal at about 2.5 GPa. The anisotropy in the layer disappered at high pressures. The resistivity along the b-axis was about two orders of magnitude larger than that of the a- and c-axes at 3.0 GPa. Two dimensional character in black phosphorus still remained in this pressure. Black phosphorus is stable at room temperature and atmospheric pressure. However, as black phosphorus was very reactive at high temperatures and high pressures, it reacted with noble metals like Pt and Au and many other substances.

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Electrical transport properties of Th₃P₄-type EuLn₂S₄(Ln=-La-Gd) with bivalent europium ions were studied. From thermoelectric power measurements, the charge carrier for electric conduction in these compounds was found to be positive holes. This is unusual finding among Th₃P₄-type sulfides, most of which are metallic or n-type semiconducting materials. Co nductivities were almost the same (ca.3×10^-5Ω^-1⋅cm^-1at room temperature) for the specimens from EuLa₂S₄ to EuNd₂S₄, but increased on going from EuNd₂S₄ to EuGd₂S₄. On the basis of the concept of percent covalency, representing the covalent contribution to the bonding in the Th₃P₄ structure, it appears that going from EuLa₂S₄ to EuGd₂S₄ makes the Ln-S bond lessionic. This covalent contribution seems to be one of the most decisive factors in their electrical properties. The conductivity of EuGd₂S₄ was sensitive to sulfur vapor pressure, obeying the relationship σ ∝ P_S2^1/6. From this result, it is concluded that the following equilibrium reaction takes place over the temperature range from 400 to 500°C
Both Eu and S in EUGd₂S₄ were sublimed by the heat-tre a t m e n t a t h i g h t e m p e r a tures under a high vacuum. The heat-treated samples were classified into two groups on the basis of their electrical transport behaviors. One group comprises semiconducting materials treated at 1500°Cand 1600°C. The electric conduction is based on an electron hopping between localized states which are produced by the sublimation of Eu and S atoms. The other group comprises metallic materials treated at 1700°C and 1800°C. Their electrical transport is due to a band conduction.

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The glass-forming region was determined for the system AgI-Ag₂O-B₂O₃. Infrared spectra, glass transition temperatures, electric conductivities, and transport numbers of silver ions and electrons were measured for the glasses prepared. Glasses were obtained even for the compositions with the mole ratio Ag₂O/B₂O₃= 3. Infrared spectra showed that each glass contained both BO, and BO₄ groups and the wave numbers of absorption peaks characteristic of each group remained unchanged with the variation of glass composition. Ion exchange of Ag⁺ ions in glass with K⁺ ions in KBr revealed that the non-bridging oxygen was present in BO₃ groups only. Glass transition temperatures ranged from.110 to 390°C and showed maxima in compositions with the low AgI content, when plotted against Ag₂0/B₂O₃. The increase in glass transition temperatures did not correspond to the increase in the concentration of BO, group. The conductivity at room temperature ranged from 10^-2 to 10^-6 Ω ^-1cm ^-1, the transport number of Ag ions being unity. The conductivity increased with inceasing AgI content, but did not always increase with increasing Ag₂O content. It was speculated from this result that only a part of Ag⁺ ions in glass contributed to the ionic conduction.

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Four-point bending creep behaviour was investigated for Mn-Zn ferrite single crystals at temperatures between 1150 and 1400°C. Two types of specimen were chosen for the creep testing, one of which had [110] stress direction and the other had [211] stress direction (Fig.1). Sigmoidal transient creep curves were observed, followed by steady-state creep regions (Fig.2). Deformation mechanism was inferred from the stress dependence of steady-state creep rate. Stress exponents were approximately 3 (Fig.3 and 4), suggesting that the deformation was controlled by dislocation climb as expected on the basis of the results of creep testing for coarse-grained Mn-Zn ferrite polycrystals. Apparent oxygen lattice diffusion coefficients were calculated according to the Nabarro-Weertman equation (Fig.5). Although oxygen diffusion in [110] and [211] specimens showed nearly similar temperature dependence, the values of diffu sion coefficient were different between the two specimens. The higher values for [211] specimens were related to the higher etch pit density in deformed [211] specimen than in (110)specimen. Shear moduli for polycrystal were used in the present investigation, but these results require different elastic moduli and/or the constant (β in Eq.5) for [110] and [211]specimens.
Polygonization was observed in deformed specimen by chemical etching (Fig.7), which was considered to be the result of dislocation climb (diffusion).

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Large single-crystals of Bi₁₂SiO₂₀were grown by means of the Czochralski method under various growing iconditions. A pulling speed of 1 mm/h and a crystal rotation rate of 20 rpm were found to be the best conditions for growing a single-crystal of 33∼37 mm in diameter with high optical quality. These conditions made the shape of the crystal-melt interface so flat that the crystals might not contain any kind of defects such as bubbles, cores, strain or cracks.
On the basis of the above results, large single-crystals with a diameter of 50 mm were grown under a pulling rate of 0.6∼1.0 mm/h and a rotation rate of 10∼20 rpm by using a newly developed automatic pulling system. The single-crystal had good optical quality in that birefringence due to inhomogeneity was less than 1/10⁴ over the entire plane, normal to the pulling direction (Fig.10), and it also exhibited a high electro-optic effect of γ₄₁/mV^-1 5×10¹²and pronounced wavelength dependence of photoconductivity.
Bi₁₂SiO₂₀ Crystals grown under the above conditions were applied to various optical devices, i. e., optical switches, optical sensors for measurement of high electric field intensity, incoherentto-coherent image converters, and volume hologram devices, These devices are promising in the field of optical fiber communication systems and optical information processing systems.

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A study on the positive temperature coefficient of resistivity (PTCR) in porous semiconducting barium titanate ceramics has been made from the points of view of both the chemical composition and microstructure. The porous BaTiO₃ ceramics with relative densities in the range of 60 to 93% were prepared using barium titanium (IV) bis(oxalate)oxide as a starting material and Sb₂O₃ as a doping substance.
The present porous BaTiO₃ cer amics exhibited a very large PTCR effect of more than seven orders of magnitude, and a new method for preparing PTCR materials with large PTCR effects has been established.

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In order to improve the mechanical properties of an aluminum titanate ceramic which has a low thermal expansion coefficient, effects of seven additives were investigated. Some additives dissolved in aluminum titanate (Fig.3), and expelled Al₂O₂ as fine particles of corundum or reacted with Al₂O₂ or TiO₂ to form fine particles of certain compounds (Table 5). These particles were distributed among grain boundaries of the aluminum titanate and inhibited growth of the grains. The additives were effective to produce a fine grained dense ceramic (Fig.5, 6). Among the additives, ones which did not form large aggregates of highly oriented aluminum titanate particles, i. e., MgO added for oxide mixture (Al₂O₂+TiO₂) and MgO or ZrO₂ for alumingm titanate powder, increased the mechanical strength of the aluminum tita nate ceramic markedly (Table 4). SiO₂, which formed liquid phases at comparatively high temperature, promoted the densification of the aluminum titanate body, but did not promote the growth of the aluminum titanate grains. The liquid solidified as glassy phase among the aluminum titanate grains, resulting in the decrease in the formation of cracks between the grain boundaries, and the addition of SiO₂ also increased the mechanical strength of the ceramic appreciably (Table 4). Despite of their comparatively high mechanical strength (300∼530 kgf/cm²), the aluminum titanate ceramics still kept their low thermal expansion coefficient (1-2×10-6/°C in the temperature range of RT to 1000°C), and did not show any tendency of the deterioration of their excellent properties after the repeated heat treatment (Fig.9, Table 6). Further, the ceramics showed little or no sign of the decomposition to corundum and rutile after heating at temperatures below 1250°C (Fig.10).

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The adsorption behavior and immobilization of caesium from aqueous solutions were studied by the use of crystalline hydrous titanium dioxide (TiO₂⋅n H₂O) fibers as ion-adsorbents. Two kinds of adsorbents were prepared one, flux method sample, was obtained by extracting potassium from potassium tetratitanate (K₂Ti₄O₉) fibers grown in a K₂MoO₄ flux melt, and the other, melt method sample, from potassium dititanate (K₂Ti₂O₅) fibers grown directly from the melt of stoichiometric composition. Maximum caesium uptake from a caesium hydroxide solution resulted in the flux method sample composition of Cs₂Ti₅O₁₁⋅4 H₂O by each adsorbent and the melt method sample composition of Cs_1.8H_0.2Ti₆O₁₃⋅5H₂O, and the ion-exchange capacities of the two compositions were 5.0 meq/g and 3.5 meq/g, respectively.
The adsorbed caesium was immobilized as a mineral phase of t he hollandite structure, caesium priderite (CsxAlxTi_8-xO₁₆, 1.5<x<2), which was obtained by compositional and structural modifications of the obtained caesium titanate. The most stable immobilizer was produced by sintering the mixed phase of casium priderite and rutile, and its caesium leachability in pure water was 4.88 × 10^-9g/cm²⋅day.

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Thermal dehydration of amorphous calcium phosphate (ACP) was studied by means of thermogravimetry. The line width of NMR for proton in ACP was measured in the temperature range -100°C to a room temperature. The samples of ACP, heated below 500°C, absorbed again a certain amount of water vapor, while no rehydration of ACP occurred after dehydration above 650°C. The higher the dehydration temperature for ACP was, the smaller the amount of the absorbed water was. Some part of water in rehydrated ACP was difficult to be removed under a reduced pressure at room temperatures. The presence of such water was explained in terms of the extremely small pores or narrow interstices in dehydrated ACP. The line width of NMR indicated that the water in ACP was in an intermediate state between liquid and solid-lattice. It was concluded that the water molecules in ACP were similar to those in gels in consideration of the dehydration behavior described above.

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Changes in surface area and pore size distribution during the thermal treatment of MgHPO₄⋅3H₂O (DMP 3) were investigated by nitrogen adsorption-desorption at 77 K. The surface area and pore volume were found to increase markedly up to 700°C in the course of a dehydrationcondensation and subsequent crystallization process as shown below:
Between 300 and 500°C mesopores of mainly 20∼50Å radii were formed, and widened above 600°C.
On the basis of the results from density measurements, it is considered that primary particles are produced in the original powder and contracted during the reactions and the crystallization above 400°C, while the apparent morphology of the powder remains unchanged. The increase of the surface area up to 700°C may be due to the pore structure developed by the contraction. On the other hand, the decrease of the surface area above 700°C will be explained in terms of crystallite growth due to sintering.

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The vaporization of tricalcium silicate (Ca₃SiO₅) was studied in the temperature range from 1423 to 1900°C under a vacuum and in the temperature range from 1397 to 1749°C under argon atmospheres with p_H2O= 0.03∼0.39 atm. Under the former conditions, CaO component predominantly vaporized from the Ca₃SiO₅ and dicalcium silicate (Ca₂SiO₄) formed at the surface of the original Ca₃SiO₅. The Ca₂SiO₄ also vaporized congruently with almost half of the CaO component vaporization rate. The Ca₂SiO₄ formed at the surface was in δ-form and showed a tendency to orient to the (031) plane after cooling. Under the latter conditions, only CaO component vaporized from the Ca₃SiO₅ through the following reaction: Ca₃SiO₅(s) +H₂O(g)= Ca(OH)₂(g)+Ca₂SiO₄(s). After cooling the Cl₂SiO₄ formed at the surface was destroy ed owing to dusting due to the transformation to γ-type. The formation energy of the Ca₃SiO₅from the Ca₂SiO₄ and CaO was shown to be almost zero.

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In the phase diagram of the ZrO₂-CaZrO₃ region, the extent of cubic solid solution, the stability region of the compound CaZr₄O₉ and their phase relation still remains to be investigated. The present study was undertaken for obtaining information about the temperature dependence of the phase boundary line between cubic solid solution (or CaZ₄O₉) and CaZrO₃. The amount of coexistent CaZrO₃ was determined indirectly from the CaCrO₄ produced by the reaction with Cr2O₃. The mixed powders of CaCO₃ and ZrO₂ ranging in 20∼50 mol% of CaCO₃ were heattreated at the temperature up to 1800°C with 100°C steps. They were then reheated with Cr2O₃in air, followed by the spectrophotometric determination of the Cr (VI) ion. From the experimental results, it was concluded that the boundary line was very similar to that of the phase diagram by Stubican et al.

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Microstructure in the GeO₂ glass was studied by calculating the small angle Xray scattering (SAXS) intensity. The net SAXS was obtained by subtracting the theoretically calculatted intensity, which is the skirt of hallow of Xray diffraction, from the observed intensity by Pierre et al. It has been shown that the size of heterogeneities in the GeO₂ glass was calcu-l ated to be 1.9 nm from Guinier plot (Fig.2) of the net SAXS intensity. It has been considered that the heterogeneities were caused by the fluctuation of the frozenin density in the GeO₂ glass.

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Non-crystalline films were prepared by the twin-roller quenching of the systems of TiO₂with CaO, BaO, MgO and Al₂O₃. Electrical conductivities of these non-crystalline films and their changes on heating were measured by the complex impedance method within the frequency range between 500 kHz and 100 Hz. Electrical conductivities of the non-crystalline films were about two orders of magnitude smaller than those of their corresponding crystalline forms. Crystallization induced a remarkable change in the relation between complex impedance and frequency.

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