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The effects of different B-site elements on the Curie points of the PbTiO3-Pb(M1/3Nb2/3)O3 and 0.99BaTi03-0.01Ba(M1/3Nb2/3)O3 series (M = Ca, Mn, Fe, Co, Ni, Cu, Zn), were examined. The Curie point was high when M was copper, while it was low when M was nickel. This was caused by the Jahn-Teller effect in the CuO6 octahedron keeping the Curie point high. For the 0.99BaTiO3-0.01 Ba(M1/3Nb2/3)O3 systems, the Curie points were correlated with axial ratioc/a.

An attempt has been made to use extended X-ray absorption fine structure (EXAFS) to study the polymorphs (beta, gamma and alpha types, and ramsdellite) of manganese dioxides. The ratio of (1 × 1) tunnels to (1 × 2) tunnels for the intergrowth structure of gamma-MnO2 was found to be as high as 46.2%. The relation between the valence state of manganese ions and the threshold absorption energy (E0) was clarified andE0 was found to be in the following order: beta>gamma>alpha (K)>alpha (Ba). EXAFS presented a possibility of nondestructive analysis of the valence state of manganese ions in manganese dioxides.

The effect of rare earth oxide additions on the anatase-rutile transformation in doped TiO2 was investigated. Y2O3, La2O3, CeO2, Nd2O3, Sm2O3, Gd2O3, Tb4O7, Ho2O3, Dy2O3, Tm2O3 and Yb2O3, were found to suppress the transformation. The transformation process occurs in three stages. In the first stage, rare earth metal ions dissolve into interstitial sites in anatase. The resulting decrease in oxygen vacancies caused by the solid solution suppresses the nucleation of the transformation. In the second stage, the activation energy of the transformation was found to be 124 ± 3 Kcal/mol and 138 ± 4 Kcal/mol for pure anatase and anatase with 1 mol% Dy2O3, respectively. The transformation mechanism of this stage is not necessarily affected by additives. The final stage is affected by the amount of rare earth oxide-titania compound phase.

Mechanical and dielectric strength distributions were studied for variously surface-finished TiO2 ceramics. Roughly finished specimens showed a small Weibull modulus for both kinds of failures, and clear analogies between mechanical and dielectric strength distributions were found in both rough-and fine-surface specimens. The validity of the dielectric strength measuring method as an alternative method to evaluate the structural reliability of brittle ceramics is discussed.

The electrical behaviour of bcc 6Bi2O3·SiO2 sintered specimens was investigated by measuring electrical conductivity, ionic transference number, Seebeck coefficient and cationic composition. The total conductivity,σt, in the\(P_{{\text{O}}_{\text{2}} } \) range from 105 to 10−7 Pa showed mixed conduction where electron conductivity was predominant below 10−1 Pa and where σt could be expressed by the equation $$\sigma _{\text{t}} = \sigma _{\text{i}} + \sigma _{\text{p}}^0 (P_{{\text{O}}_{\text{2}} } /10^5 {\text{Pa}})^{{\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 4$}}} + \sigma _{\text{n}}^{\text{0}} (P_{{\text{O}}_{\text{2}} } /10^5 {\text{Pa}})^{ - {\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 4$}}} $$ whereσi,σp0 andσn0 represent the oxygen ionic, hole and electron conductivities, respectively, at a\(P_{{\text{O}}_{\text{2}} } \) of 105 Pa. The silicon concentration in the specimen was slightly less than the theoretical value. The cation atomic ratio, Si/Bi (theoretically 1/12), was estimated as 0.93∼0.95/12. Schottky-type defects of silicon and oxygen vacancies were proposed to explain a much higher oxygen ionic conductivity in the sintered specimens than that reported for single crystals.

It was newly found that a larger amount of ZnO vaporizes from (Zn0.5Co0.5) O⋅1.3 Al2O3 than from (Zn0.5Ni0.5) O⋅1.3 Al2O3 when heated above 1300°C.Cation vacancies tend to occupy B-sites in (Zn0.5Co0.5) O⋅1.3 Al2O3 and A-sites in (Zn0.5Ni0.5) O⋅1.3 Al2O3. The difference of vacancy distributions was considered to cause the vapor pressure differences.Diffusional processes were also considered and it was assumed that Zn2+ diffuses outward by way of interstitial sites in (Zn0.5Co0.5) O⋅1.3 Al2O3, and that the driving force of the inward diffusion of Co2+ or Ni2+ is the difference of cation vacancy concentration between the surface and the inside of the pellet. The activation energies of interdiffusion of Zn2+ and Co2+, or Zn2+ and Ni2+ were 110kcal/mol and 78kcal/mol, respectively.

The early stage of hydration of CaO⋅2Al2O3 was investigated. Hydration was carried out mainly in a diluted water suspension. The rate of hydration of CaO⋅2Al2O3 was greatly affectted by the water/solid ratio and the synthetic condition of specimen, while the mechanism of hydration remained unchanged under these conditions. In particular, formation of crystalline hydrates was retarded with increasing water/solid ratio. At the earliest period of hydration, the reaction rate was slow and hydrates were not found. It appears that this period corresponds to a nucleation stage of gibbsites. In the following period precipitation of gibbsite was observed, in which the concentrations of CaO and Al2O3 in the liquid increased rapidly, accompanied by an increase in CaO/Al2O3 molar ratio. In this period the reaction proceed by the dissolution-crystallization mechanism. Finally, different hydrates such as 2CaO⋅Al2O3⋅8H2O began to precipitate and the rate of hydration was accelerated.

Enhancement of ionic conductivity was found in the system of SrCl2 and Al2O3 mixture. The enhancement of Cl- conductivity depended on the composition and the grain size of Al2O3. From these results, it was considered that the interface between SrCl2 matrix and Al2O3 particles played a role in giving rize to high ionic conductivity. The effective thickness and the conductivity of the interface layer were estimated by using a simple mixture model. The validity of this estimation was supported by the results of measurement for a modeled sample.

The relation between electrical conductivity and effective thickness of grain boundaries is given for two types of domains as typical patterns of the composite body by mathematical procedures.

The electrical properties of poly-phase ceramics in the system Li2O-ZnO were studied. The specimens obtained were confirmed to be composed of Li2ZnO2, ZnO and some Li4ZnO3, by X-ray diffraction. Li2ZnO2 was assumed to possess a hexagonal structure with cell parametersa=0.812 nm andc=0.673 nm. Electrical conductivity increased with increasing temperature up to 420° C, and decreased abruptly above 420° C. The temperature dependence of the ionic transference number showed that ionic conduction was dominating above 300° C, while mixed conduction occurred below 300° C. The dependence of electrical resistivity on relative humidity was also measured at room temperature. Electrical resistivity exponentially decreased five orders of magnitude with increasing relative humidity from 5 to 95%. The decrease in electrical resistivity with increasing relative humidity might be caused by LiOH formed on the surface of the specimens.

Electrical breakdown strengths of single crystal and polycrystalline MgO were measured at 1000 to 1400‡C. Temperature and thickness dependences of the breakdown strength of single crystal MgO firmly indicated that the electrical breakdown was of thermal type. A high correlation between the ionic conductivity and the breakdown strength was found, which together with the observed melted track suggested that the electrolytic decomposition took place. The breakdown strength of single crystal MgO decreased with increase in the dislocation density. The breakdown strength of polycrystalline MgO indicated a significant effect of the microstructural factors, though a quantitative evaluation was impossible in the present study.

弗化カルシウムの焼結において, 原料粉末に吸着している水分の影響を調べた. 単にアルゴン中で焼結した場合と, 水分を除去しつつ減圧下で焼結した場合とを比較した. この結果, 水の存在は, 焼結組織および焼結体のイオン伝導度に大きな影響を及ぼしていることが認められた. 酸素をドープした単結晶の伝導度との比較から, 水は弗化カルシウムと反応し, 弗素空孔を生じていると結論された.

Mechanical and dielectric strength were measured for three types of BaTiO3 thick films prepared under the different processing conditions. In any case, Weibull moduli for both strength distributions were identical in each type of films, though they differed among three types. The results indicated that dielectric strength measurement is a promising alternative method to distinguish the structural reliability change as influenced by processing parameters before firing within the framework of the same fabrication method.

The interdiffusion coefficients \ ildeD of Zn2+ ions in aluminium cobalt(II) oxide (cobalt aluminate) and aluminium nickel(II) oxide (nickel aluminate) were measured. In the former \ ildeD is independent of the concentration of the composition-dependent cation vacancies, while in the latter it decreases with increase in the concentration of cation vacancies. The difference in the distribution of cations and cation vacancies in the spinel lattice has a great effect on the interdiffusion coefficients of Zn2+ ions. The results were interpreted by means of the vacancy mechanism for Co2+ and Ni2+ ions and the interstitial or interstitialcy mechanism for Zn2+ ions. The activation energy is independent of the concentration of Zn2+ ions or cation vacancies; 355 kJ mol−1 for cobalt aluminate and 364 kJ mol−1 for nickel aluminate.

The electrical conductivity and Seebeck coefficient of single-crystal NiO were measured at 1100 to 1400° C. The activation energies for conductivity and thermoelectric power were 84.1 and 76.5 kJ mol−1, respectively, which was interpreted as showing band-like conduction occurring at high temperatures. Doubly ionized cation vacancies were believed to be the dominant point defects, and the impurity effect gave rise to a $$P_{{\text{O}}_{\text{2}} }^{1/5} $$ dependence of conductivity. The effective mass of a hole, m *, was calculated based on a band-conduction scheme using the literature value of the deviation from stoichiometry, δ, and the hole mobility μ. The value of m * was in the range 0.8 to 1.0m 0, and slightly decreased with increasing temperature.

Gas sensitivity of CuO/ZnO hetero-contact was investigated at 160–340 °C. The gas sensitivity changed not only with the kind of gases and measuring temperature but with the voltage applied to the hetero-contact. Very high sensitivity and selectivity for CO gas was observed at 260 °C under the applied voltage of 0.1–0.9 V.

Electrical conductivity was measured for fcc Bi2O3 solid solutions in Bi2O3ZrO2Y2O3 system, which were made by using Y2O3-doped Bi2O3 (BY) and Y2O3-doped ZrO2 (ZY). In the system with Y concentration of 20 at%, the fcc phase was formed at 0–10 mol% ZY and the oxygen-ion conductivity decreased with an increase in ZY. In system with Y2O3 concentration of 10 mol%, metastable fcc phase was formed at 0–14 mol% ZY and the conductivity below 600°C increased with an increase in ZY in the fcc monophase region and decreased in two-phase (BY and ZY) region. There was a correlation between lattice constant and conductivity at low temperatures. Addition of ZrO2 was found to have some contribution to stabilization of fcc Bi2O3 but to be not so effective as that of Y2O3.

The mechanism for the vaporization of ZnO from powders of (Zn0.2Co0.8)O⋅1.1Al2O3 and (Zn0.2Ni0.8)O⋅1.1Al2O3 spinels was studied at 1335° to 1500°C in vacuum of 3×10-5 to 10-4 Torr. The vaporization of ZnO occurred in two stages-vaporization of constant rate at the first stage and of decreasing rate at the second stage. The observed fractions of ZnO vaporized deviated from the calculated values at higher temperatures. The results were interpreted with the assumption that the exsoluted corundum layer at the powder surface sintered more densely at higher temperatures causing the decrease in vaporization surface area. The ratio of the concentration of ZnO at the surface to the initial concentration at the time the vaporization mechanism changed from the first to the second stage was approximately 0.9 and independent of temperature.

On mesure la conductivite electrique dans une gamme de temperature allant de 25 a 800°C. Determination de l'influence de Po 2

The electrical resistivity of ZnO doped with Al2O3 was measured in air and under reduced pressure (∼0.5 mm Hg) in the range from 30° to 680°C as a function of the degree of sintering. The data obtained were explained in terms of the effects of the microstructure of the sintered body and the chemisorbed oxygen. There are two mechanisms of electrical conduction involved, only one of which is affected by the microstructure.

The ionic transference number, the electrical conductivity, and Seebeck coefficient of Ni 1− x Mg x O (0.1 ≤ x ≤ 0.9) were measured as functions of temperature (900–1400°C) and oxygen partial pressure (10 2 –10 5 Pa). The contribution of ionic conduction to the total conductivity of Ni 0.9 Mg 0.1 O was of the order of 10 −3 −10 −2 at 900–1300°C, which led us to assume that the electronic conduction was predominating in Ni 1− x Mg x O ( x ≤ 0.9). The electrical conductivities of both undoped and Al-doped Ni 1− x Mg x O depended on the 1 4 power of P O 2 , which indicated a significant impurity effect on the defect equilibria and was interpreted as showing that doubly ionized cation vacancies were the dominant point defects at high temperatures. Analyses of the difference in the temperature dependences of conductivity and Seebeck coefficient showed that band-like conduction took place in the NiO-rich composition range ( x ≤ 0.1), while thermally activated hopping of small polarons occurred in Ni 1− x Mg x O with x ≥ 0.3. The calculated drift mobility abruptly decreased in the composition region where the conduction mechanism changed.

Electrical conduction in bccγ-Bi2O3 doped with Sb2O3 was investigated by measuring electrical conductivity, as a function of temperature and oxygen partial pressure\(P_{{\text{0}}_2 } \), and ionic transference number. Theγ-Bi2O3 doped with 1 to 3 mol% Sb2O3 was stable up to 550° C and showed an oxygen ionic conduction in the\(P_{{\text{0}}_2 } \) region of 105 to 10−9 Pa. As the Sb2O3 content increased, ionic conductivity increased up to 2.5 mol % Sb2O3 (1.8×10−3Ω−1cm−1 at 500° C) and then decreased. However, the activation energy for ionic conduction remained almost unchanged. It was proposed that theγ-Bi2O3 contains a lot of oxygen vacancies and incorporated Sb5+ ions at tetrahedral sites which affect the concentration of oxygen vacancy effective for conduction.

Physical factors correlating with the Curie-Weiss temperatures of displacive-type f erroelectrics and antif erroelectrics were surveyed. For oxide compounds with perovskite and tungsten-bronze structures, the covalent bond energy between an A-site ion and an oxygen ion was found to show a high correlation with their Curie-Weiss temperatures, Effective charges of the ions in these compounds, which were estimated by an extended Sanderson's theory, supported highly covalent nature of their chemical bonding. Relation between Curie-Weiss temperatures and ion radii were also examined.

Thermal responses (thermal time constant τ and responsivity RV of resistance changes) to infrared radiation were measured for SiC-fiber thermistors. Four kinds of commercial SiC fibers (Nicalon) with different resistivities (0.37-3.0kΩ·cm) and diameters (7-14μm) were used as the thermistors. The thermal time constants decreased with decreasing length of the fibers (distances between electrodes) in a series of thermistors using the same kind of fibers. In a thermistor made of separately arranged fibers with a low resistivity (0.37kΩ·cm) and of a small number (n=22), a small thermal time constant of 11 msec was obtained. A relation of τ∝H⋅RV (H: heat capacity) was derived theoretically, and measured values in the thermistors of separately arranged fibers satisfied above relation. It was suggested that the thermal time constant can be controlled by selecting SiC fibers with adequate resistivity and diameter and the shape of a thermistor (numbers and length of fibers).

Changes in resistivity and chemical changes in reducing gases were measured for porous zinc oxide ceramics with and without a platinum catalyst at 300° and 400°C to examine the gas sensing mechanism and the effect of platinum additions. Reducing gases were oxidized to CO2 and Hz2 on the sensor surfaces. Platinum addition promoted the oxidation of reducing gases but did not lead to an increase in the resistivity change at 400°C. The reaction sequences for the gas sensing process are proposed, taking into account partially oxidized intermediates of hydrocarbons and oxidation on platinum without an electron transfer process.

Electrical conductivity and thermoelectric power were measured on undoped and Li- or Al-doped NiO at 800°-1400°C. The electrical conductivity (σ) of Li-doped NiO was independent of both oxygen partial pressure (PO2) and temperature at low PO2, which yielded the calculated hole mobility of 0.43cm2/V·s. From the temperature dependence of σ at PO2=105Pa for Al-doped NiO and the hole mobility of Li-doped NiO, the deviation from stoichiometry δ in Ni1-δO was obtained: δ=7.75×10-2exp(-16200/RT). The electrical conductivity for both undoped and Al-doped NiO varied with PO21/4 at a constant temperature, thus leading to the conclusion that doubly ionized nickel vacancies were dominant at high temperatures. The temperature dependence of Seebeck coefficient was inexplicable by means of a thermally activated hopping mechanism indicative of rather wide band conduction of electron holes.

The formation of SiC hollow particles by gas-phase reaction in the silane-methane-hydrogen system was studied at temperatures from 1200 to 1400° C. Synthesized powders were analysed by means of the thermogravimetry, X-ray diffraction, transmission electron microscopy, infrared irradiation, etc. The powders synthesized at 1200 to 1300° C consisted ofβ-SiC and silicon phases, but they became almost hollowβ-SiC particles at 1400° C. The composition, particle size, and shell thickness of the synthesized particles were dependent on the reaction conditions. From lattice parameter measurements, a certain amount of excess silicon was verified to be incorporated into theβ-SiC lattice. On the other hand, excess carbon existed, for the most part, as an amorphous phase not forming solid solutions withβ-SiC. Transmission electron microscopy observations and infrared absorption measurements have shown that excess carbon is contained within the shells of hollow particles, while unreacted excess silicon exists as a crystalline phase mostly in the cores of the particles.

Electrical conduction in tetragonal β-Bi2O3 doped with Sb2O3 was investigated by measuring electrical conductivity, ionic transference number, and Seebeck coefficient. The β-Bi2O3 doped with 1 to 10 mol% Sb2O3 was stable up to 600°C and showed an oxygen ionic and electronic mixed conduction, where the electron conduction was predominant at low oxygen pressures. The oxygen-ion conductivity showed a maximum at 4 mol% Sb2O3, whereas the activation energy for the ionic conduction remained unchanged for 4 to 10 mol% Sb2O3-doped specimens. These results were interpreted in terms of the oxygen vacancy concentration and the distortion of the tetragonal structure. The electron conductivity and its oxygen pressure dependence decreased with increasing Sb2O3 content. The fact that Sb5+ is partially reduced by excess electrons in heavily doped β specimens at low oxygen pressures is explained.

Mesures de la conductivite electrique de melanges Al 2 O 3 /SrCl 2 ; influence de la composition, de la taille des particules Al 2 O 3 et de la methode de preparation. Role de l'interface? evaluation de l'epaisseur et de la conductivite effective d'une couche interfaciale par un modele de melange simple

A new type of reducing gas sensing system has been developed based on changes in ionic conductivity. Though it is well known that the resistivity of n-type semiconductors such as ZnO decreases on the introduction of reducing gases, that of thin films sputtered on silica glasses in the present study (which had Ag electrodes) increased with the introduction of reducing gases. This abnormal property is due to the change in the ionic resistance of Ag+ incorporated from the electrode.