Luminescence properties of highly <100>-oriented Y₂O₃:Eu³⁺ whiskers obtained by chemical vapor deposition on YSZ substrate have been investigated over a wide temperature range. A considerable thermally stimulated increase of the red Eu³⁺ emission intensity was found under the excitation by the wavelength corresponding to the intrinsic transition within the Eu³⁺ ion, in contrast to the charge-transfer excitation. This behavior is discussed on the basis of the results of the time-decay measurements of the emissions from each electronic level of the ⁵D_J (J=0, 1, 2) manifold in the temperature range 300 K-1155 K. A model is proposed in which this thermally stimulated increase is assigned to the multiphonon relaxation from the upper-lying ⁵D_J (J=1, 2) levels to the terminate level ⁵D₀, responsible for the intensive red emission.

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(Sr, Ba)TiO₃ FGM (Functionally Gradient Material) ceramics were fabricated by hot isostatic pressing to obtain flat temperature dependence of dielectric constant with a large value in a wide range of temperature. The FGM compacts were prepared by stack of each green compact with different composition and were fully densified by hipping at 1200°C for 1 h under 200 MPa. Dielectric constant of the hipped FGM was about 3400 in the temperature range of 10∼50°C. Application of high pressure (200 MPa) at low temperature (900°C) and then heating up to 1200°C, a flat temperature range of dielectric constant were over wide (-5∼80°C) and grain size of hipped FGM was remarkably suppressed compared with the FGM fabricated by conventional hipping process. Using fine powders prepared by sol-gel process as raw materials, dielectric constant was obtained about 3600 and was constant over the wide range of temperature (0∼90°C).

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To successfully synthesize CaBi₄Ti₄O₁₅ (CBT) thin films, pre-sintered CBT targets were sputtered at room temperature in argon on the (111)Pt/Si substrates, followed by annealing at temperatures ranging from 600°C to 700°C. CBT films annealed at 600°C, 650°C and 700°C all exhibited well established ferroelectric hysteresis loops. A P_r of 5.09 μC/cm² and E_c of 48.0 kV/cm were measured at 4.5 V and room temperature for the CBT film annealed at 700°C, with a respective dielectric permittivity and dielectric loss of 413 and 0.075. Both P_r and E_c increase with rising temperature. At 120°C, a P_r of 6.10 μC/cm² and E_c of 58.0 kV/cm were measured at 4.5 V. The observed ferroelectric properties of CBT films can be correlated to their structural features, which were controlled by the experimental parameters selected for magnetron sputtering.

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Ba_0.75Y_0.166Nb₂O₆ (BYN) thin films were deposited on (100)MgO and (100)Si substrates by RF magnetron sputtering for the first time. The thin films deposited on MgO substrates show single crystalline layer with the (001) orientation perpendicular to the substrate plane confirmed by X-ray diffraction 2θ scans. However, X-ray polefigure revealed that the films have two in-plane orientations. The unit cell of BYN is rotated in the plane of the film by ±15° with respect to the unit cell of the MgO substrate. The thin films deposited on Si substrates are polycrystalline with random orientation.

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Ferroelectric properties and polarization fatigue characteristics of Pt/(Pb_0.925La_0.075) (Zr_0.4Ti_0.6)_0.981O₃ (PLZT)/PbTiO₃ (PT)/Pt capacitors fabricated by crystallizing amorphous PLZT films at 500°C for 1 h under high pressures of 8.8-176.5 MPa using hot isostatic pressing (HIP) are investigated. The films HIP-treated under 26.1 MPa showed almost complete (001)-orientation and their degree of c-axis orientation, α, reached up to 0.99. The P-E hysteresis loops of films HIP-treated under 8.8-176.5 MPa gradually changed from a rectangular shape with a remanent polarization 2P_r=25.9 μC/cm² and a coercive field 2E_c=76.8 kV/cm to a flat shape with 2P_r=9.8 μC/cm² and 2E_c=54.4 kV/cm with increasing HIP pressure. The pulse-derived switchable polarization (Q_sw) of all the samples HIP-treated under high pressure over 26.1 MPa hardly showed the fatigue degradation up to the switching cycles of 3×10¹⁰.

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The (Y,Yb)MnO₃ films were prepared on Pt/TiO_x/SiO₂/Si and Y₂O₃-buffered n-type Si(111) substrates using alkoxy-derived precursor solutions and followed by rapid thermal annealing in Ar. The (Y,Yb)MnO₃ films crystallized to hexagonal phase and had high crystallinity and high degrees of c-axis orientation. It was found that the substitution of Y by Yb in YMnO₃ lowered the crystallization temperature. The YbMnO₃ film crystallized at 700°C in Ar showed good ferroelectric properties. The retention time was over 10⁵ s and the polarization did not change after 10¹⁰ switching cycles. The leakage current density of the Pt/YbMnO₃/Y₂O₃/Si capacitor was below 1.0×10^-8 A/cm² at an applied voltage of 5 V. The counterclockwise C-V hysteresis induced by ferroelectric polarization switching was observed in the Pt/YbMnO₃/Y₂O₃/Si capacitor.

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Metallic SmS and Sm₃S₄ thin films, in which Sm ions possess divalent and trivalent mixed state, were prepared on Si wafer substrate at 20°C using Sm₂S₃ and Sm₂S₃/Sm mixed targets by rf magnetron sputtering. Even though only Sm₃S₄ phase was formed using a Sm₂S₃ target, both metallic SmS and Sm₃S₄ films were deposited using Sm₂S₃/Sm mixed targets depending on substrate positions. The possible formation processes of metallic SmS and Sm₃S₄ thin films were proposed. Irradiation experiments were performed using a femtosecond laser at 800 nm with a pulse duration of 120 fs and a repetition rate of 10 Hz. No macroscopic changes were observed in Sm₃S₄ thin films at a fluence <1.2×10⁴ J•m^-2 and the film ablation occurred over 1.2×10⁴ J•m^-2. On the other hand, in the case of metallic SmS films, with the fluence of 5.0×10³ J•m^-2, the metallic to semiconductor phase transition occurred, and the film ablation occurred when the fluence was over 7.0×10³ J•m^-2. X-ray photoelectron spectroscopy study revealed that Sm²⁺ (4f) peak near the Fermi energy was shifted about 0.3 eV in the irradiated metallic SmS film. The change in the electronic structure change of Sm for the films was discussed.

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The doping effect of rare-earths on the temperature-capacitance characteristics of MLCCs with Ni electrodes has been investigated for a BaTiO₃-MgO-Rare-earth system. The temperature dependence of capacitance was reduced with smaller radii ions such as Ho, Er, Tm, Yb, and Lu, with Tm, Yb, and Lu being especially effective. The Curie temperature also shifted towards a higher temperature by the doping of smaller ionic radii rare-earth elements. On the other hand, the temperature dependence of capacitance increased and a decrease in the insulation resistance was observed for the larger ionic radii rare earth elements such as Tb and Gd. Ionic radii of rare-earth dopants can be an important factor in controlling the temperature-capacitance characteristics as well as improving the reliability. The reason for the increase in Curie temperature originates form the residual tensile stress generated by the mismatch in the lattice constant between the BaTiO₃ core and diffused aria. Ni electrode MLCCs with X8R characteristic specification for automotive use have been developed using rare-earth dopants with smaller ionic radii such as Tm, Yb, Lu.

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Highly temperature stable Pb(Zr, Ti)O₃ ceramics have been developed with planar mode of electromechanical coupling factor (k_p) and frequency constant (N_p). In order to improve the temperature stability of piezoelectric properties, a PZT composite with stacked PZT53/47, 52/48 and 51/49 layers was fabricated and evaluated in terms of the temperature dependence of k_p and N_p between -190°C and 190°C, compared with 10 mol% (Li_0.5La_0.5) doped Pb(Zr, Ti)O₃ (PLLZT) ceramics. PLLZT ceramics have stable frequency constants to temperature, whereas its k_p values become lowers than 50% with increasing temperature. On the other hand, the newly developed gradient PZT composite proposed in this study had stable temperature properties of k_p and N_p in the wide temperature range. In addition, the k_p value of the gradient composite was constantly kept higher than 50%.

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Ca-doped Sr₂(Nb, Ta)₂O₇ thin films have been synthesized by the chemical solution deposition. Homogeneous and stable precursor solutions were prepared by controlling the reaction of starting metal alkoxides. The improvement of ferroelectric properties of the Sr₂(Nb, Ta)₂O₇-based films were achieved through the Ca-substitution for Sr sites in the Sr₂(Nb_0.3Ta_0.7)₂O₇ structure. (Sr_1-xCa_x)₂(Nb_0.3Ta_0.7)₂O₇ crystallized in the single-phase of (Sr, Ca)₂ (Nb_0.3Ta_0.7)₂O₇ in the case of x<0.15 without any formation of the second phase such as Ca₂Ta₂O₇. The crystallization temperature of the layered perovskite (Sr_0.9Ca_0.1)₂(Nb_0.3Ta_0.7)₂O₇ thin films on Pt/Ir/Ti/SiO₂/Si substrates was found to be below 700°C. (Sr_0.9Ca_0.1)₂(Nb_0.3Ta_0.7)₂O₇ thin films crystallized at 750°C exhibited the typical ferroelectric hysteresis loop with P_r of 0.58 μC/cm² and Ec of 80 kV/cm.

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The influence of the process parameter in the milling process on core-shell microstructure and electrical properties of X7R type multi-layer ceramic capacitors with an Ni internal electrode (Ni-MLCC) was investigated in a BaTiO₃ (BT)-Ho-Mg system. Elaborate transmission electron microscopy (TEM) observation and statistical analysis for 100 grains for each MLCC sample fired at 1320°C revealed that microstructure was dependent on the degree of damage of BT particles caused by the milling process. The rate of frequency of grains without 90° domain pattern increased, and the volumetric ratio of the shell region increased as the damage increased. It was found that the concentration gradients of Ho were observed in the shell phase for all samples, and the concentration of Ho near the grain boundaries (GBs) became poorer as the damage increased, judging from chemical composition analysis by TEM with an energy dispersive X-ray spectroscope (EDS). Furthermore, the microstructural evolution had a fatal influence on the electrical properties of MLCC. The relative permittivity decreased and the broad peak around 40°C shifted to a higher temperature as the damage increased. The insulation resistance (IR) increased and the lifetime during the highly accelerated lifetime testing (HALT) was improved as the damage increased. Measurement of the impedance response at elevated temperatures revealed that the εr of the core phase decreased, however, the relative resistivity of core phase increased with increasing damage.

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(1-y)BaTiO₃(BT)-yBi₄Ti₃O₁₂(BIT) films in the composition range up to y=0.05 were prepared on (100)MgO substrates by metalorganic chemical vapor deposition (MOCVD). The effect of composition on the microstructure, morphology and dielectric properties of the films was investigated. At y<0.03, the BIT-doped BT films were obtained, and the grain size of films increased with increasing y. BaBi₄Ti₄O₁₅ phase was identified at y=0.03. The BIT-doped BT film of y=0.01 exhibited the maximum dielectric constant of 1010 that was twice as great as that of BT film. The high dielectric constant might be resulted from the increase in grain size. The remanent polarization (2P_r) and the coercive field (2E_C) of the BIT-doped BT film of y=0.01 were 0.7×10^-2 C•m^-2 and 6.0×10⁵ V•m^-1, respectively.

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Yttria-stabilized zirconia (YSZ) films and SrO-doped YSZ films were prepared by MOCVD, and their electrical properties were investigated. (200) oriented cubic-YSZ films were obtained at 873 to 1024 K. The electric conductivity, dielectric constant and dielectric loss tangent of the YSZ films were almost in agreement with those of YSZ single crystals. Cubic SrO-doped YSZ films were obtained at the composition of 3 to 9 mol%SrO. The electrical conductivity and dielectric loss tangent of SrO-doped YSZ films were decreased with increasing SrO content, and the dielectric constant showed the minimum value of 15 at 10 mol%SrO.

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Integration of piezoelectric films on silicon wafer is becoming very important for the applications in microelectromechanical systems (MEMS). Compared with other existing methods, electrophoretic deposition is a promising, simple and cost-effective method for fabrication of piezoelectric ceramic films. In this study, commercial lead zirconate titanate (PZT) powders were deposited onto silicon wafers coated with platinum electrodes by using electrophoretic deposition method in ethanol solution. The deposition behavior was investigated under different applied voltages and deposition duration. The morphologies and microstructures of as-deposited and sintered films were observed by scanning electron microscopy (SEM). Phase development of the PZT thick films was analyzed by X-ray diffraction to optimize the processing parameters.

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Piezoelectric properties of Sr_xBi_3-xTa₂O₉ (x=0.5-1.0) [SBT(x)] ceramics were studied for the purpose of discovering bismuth layered-structure ferroelectrics (BLSFs) with large electromechanical coupling factor k_ij and mechanical quality factor Q_m. Ordinarily fired (OF) samples were prepared by a conventional ceramic technique and the sintering temperature was varied from 1150 to 1250°C. Before the piezoelectric measurement, an enhancement of the ferroelectric properties of the SBT(x) ceramics by Bi substitution was confirmed. The values of the electromechanical coupling factor with radial-extentional mode k_p for the SBT(x=0.85) ceramics sintered at 1200°C were found to be the largest (k_p=10.9%) in the SBT(x) system. The piezoelectric and related constants of SBT(x=0.8) ceramics were also evaluated. The values of k_p (10.6%) and k₃₁ (6.8%) with lentgth-extentional mode were higher than those of other OF-BLSFs ceramics with large coupling coefficients, and k₃₃ (14.0%) with lentgth-extentional mode were comparable.

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Single phase bismuth titanate (Bi₄Ti₃O₁₂, abbreviated to “BIT”) and calcium bismuth titanate (CaBi₄Ti₄O₁₅, abbreviated to “CBT”) particles have been prepared successfully by a newly developed hydrothermal method. By Scanning Electron Micrograph (SEM) observation, both BIT and CBT particles were plate like, and their particle sizes are 5 μm and 0.2-0.3 μm for BIT and CBT, respectively. By using these plate like particles, well oriented ceramics of BIT and CBT could be fabricated using the templated grain growth (TGG) method.

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The present article reviews our latest studies directed to establishing a tailor-made method for configurational design of thick film semiconductor gas sensors by several approaches aiming at improving gas sensing properties. In each approach special attention has been paid to control gas diffusivity and reactivity inside the sensors. Approaches conducted are a slide-off transfer printing method for fabricating heterolayered sensors, preparation of thermally stable ordered mesoporous powders as well as macroporus thick films, and their sensor application. Advantages of these methods in improving the sensing properties are overviewed and then remaining problems are discussed.

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In preparation for compliance with California's SULEV standard and the Euro STEP-4 standard, which will take effect in 2004 and 2005, respectively, planar exhaust gas sensors (oxygen sensor and air/fuel ratio sensor), required for fast light-off and high detection accuacy for engine exhaust feedback control, have been developed. For fast light-off time, the integration of sensor and heater elements was applied using the Alumina/Zirconia joining technique. In addition, a low temperature dependence on air/fuel ratio sensor was obtained to form the diffusion resistance layer controlling the micropore diameter and mixing chamber on the exhaust electrode. With these developments, the air/fuel ratio sensor provides high detection accuracy for a wide range of air/fuel ratios from rich to lean.

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We have already reported that a new-type complex impedance-based zirconia sensor using a ZnCr₂O₄ sensing-electrode (SE) could detect total NOx content even at 700°C. Thus, we examined here the influence of various other gases on the NOx sensitivity of the present sensor. As a result, we found that the sensitivities to H₂O as well as CO₂ were little and the NOx sensitivity was hardly affected by the presence of H₂O and CO₂ with rather high concentrations. Although we found that the sensitivities to H₂, C₃H₆ and C₃H₈ were relatively high, they might be reduced by installing an oxidation catalyst in the upper stream of the sensor element. Here, we confirmed that the NO sensitivity was almost equal to the NO₂ sensitivity and a linear relationship was observed between sensitivity and NOx concentration even in the coexistence of 8 vol% H₂O and 15 vol% CO₂. Furthermore, it was found that the NOx sensitivity was affected by the change in concentration of oxygen in the sample gas.

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The resistive oxygen gas sensors using CeO₂-ZrO₂ thick films with various ZrO₂ concentrations (0-60 mol% ZrO₂) were fabricated. In order to decrease emission of exhaust gas, resistive oxygen sensors need to have low resistivity, good sensitivity and fast response. The thick films were screen-printed on alumina substrate with a viscous paste, a mixture of the CeO₂-ZrO₂ powders and organic binder. The resistivity of thick film (ρ) as a sensor output, the oxygen partial pressure dependence of the resistivity (n: the parameter in ρ∝P(O₂)^1/n, where P(O₂) was oxygen partial pressure), and the response time of the thick film were investigated in detail. The thick film doped with 0.5-40 mol% ZrO₂ had a shorter response time, a lower resistivity, and a better oxygen partial pressure dependence of resistivity compared to the thick film doped without ZrO₂. Further, it became clear that the thick film doped with 10-30 mol% ZrO₂ had the best sensor property in the CeO₂-ZrO₂ thick films. The mechanism of the effect of ZrO₂ addition was also discussed.

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Improvement of H₂ and NO_x (NO and NO₂) sensitivities of ZnO and In₂O₃ was attempted by surface modification with mesoporous SnO₂ (m-SnO₂). The ZnO powder modified with m-SnO₂ (m-SnO₂(n)/ZnO, n: the number of cycles of the surface modification) exhibited larger pore diameter (6∼7 nm) and lower specific surface area (1∼3 m² g^-1) than those of m-SnO₂(n)/In₂O₃. H₂ sensitivity was not improved by the surface modification, but deteriorated in the case of m-SnO₂(n)/In₂O₃, whereas NO_x (especially NO₂) sensitivities of ZnO and In₂O₃ increased significantly by the surface modification. The response speeds to NO and NO₂ of m-SnO₂(3)/ZnO were fast and comparable to those of m-SnO₂(3)/In₂O₃. However, both sensors, especially m-SnO₂(3)/In₂O₃, exhibited slow recovery speeds. The difference in recovery speed between m-SnO₂(3)/ZnO and m-SnO₂(3)/In₂O₃ was suggested to reflect the different mesoporous structure of the m-SnO₂ particles loaded on the two oxide particles.

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WO₃ thin and thick film sensors have been investigated for highly sensitive detection of dilute NO₂. WO₃ powders were prepared by pyrolysis and precipitation method, and calcined at various temperatures. By using these WO₃ powders, the WO₃ thin and thick film sensors were fabricated on Au microelectrodes by suspension dropping. The entirely different thickness effect on NO₂ sensitivity was observed depending on the preparation method of powder. For the powder prepared by pyrolysis, the sensitivity decreased with increasing film thickness. On the other hand, the unique thickness effect was observed for powder prepared by precipitation, i.e., the NO₂ sensitivity had a maximum at optimal film thickness. The WO₃ thick film sensor using 400°C calcined powder showed the highest sensitivity at thickness of 7 μm. The sensitivity was as high as 45 to 0.05 ppm NO₂ at 200°C, and hardly influenced by coexisting water vapor, suggesting the possibility of environmental monitoring using WO₃ sensor. The surface morphology and the effect of oxygen partial pressure were investigated in order to clarify the unique thickness effect.

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Thermoelectric hydrogen sensor was fabricated using RF-sputtered SiGe film and Pt film as thermoelectric layer and catalyst, respectively. The influences from the preparation parameters of SiGe and Pt films and the effect from their relative area ratio were examined for optimizing the hydrogen sensing performance. With increasing the thickness of thermoelectric SiGe film, the noise level was decreased and the sensitivity was increased, but the response rate was almost not affected. A suitable cover ratio of Pt catalyst on the thermoelectric layer of SiGe film was favorable for improving the sensitivity of the sensor and enhancing the response and recovery rates. In addition, compared with the contact mounting method, the suspended sensing element presented a higher sensitivity and a little shorter response time, which could be attributed to the decrease in the thermal mass of the element with the suspending method.

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Solid electrolyte material of NASICON (sodium super ionic conductor) was synthesized through a modified sol-gel process. With the complex effect of oxalic acid added in synthesis, the stability of NASICON precursor solution was apparently improved and the crystallized NASICON phase was successfully achieved at the sintering temperature of 900°C. X-ray diffraction (XRD), Field-Emission Scanning Electronic Microscope (FE-SEM) and impedance spectrum (IS) were utilized to characterize the synthesized material. Making use of its favorite ion conductivity, a NASICON pellet type CO₂ sensor was prepared. The experiments indicated that the sintering temperature has an important influence on its sensing property. With a suitable choice of the sintering condition for the NASICON pellet, a linear relationship of the output electromotive force (EMF) with the target gas concentration for the resulted CO₂ sensor was well demonstrated in the volume gas concentration range of 0.01%-1%. The typical sensitivity is about 65 mV corresponding to a decade change of gas concentration, and the response and recovery time corresponding to 90% output EMF change is 15 s and 28 s, respectively.

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ZnO-SnO₂ composite thin film was prepared by the sol-gel method using a multi component precursor solution. The CO sensing characteristics of ZnO-SnO₂ composite thin film were examined. ZnO addition to the SnO₂ thin film was very effective to improve the CO sensitivity and the selectivity at the operating temperature range of 200°C to 500°C. The CO sensitivity of the ZnO (50 mol%)-SnO₂ thin film increased as operating temperature decreased, and it showed maximum sensitivity of 587 at 200°C.

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We have succeeded in fabricating a micropatterned SnO₂ thin film on Si substrate utilizing a Si-C linked monolayer template. The Si-C linked monolayer template was prepared by the ultraviolet (UV) lithography of 1-octadecene monolayer directly bonded to Si wafer surface. The UV irradiated area was modified into Si-O area, while nonirradiated area remained unchanged, that is, its area was composed of the alkyl chains. A film growth preferentially occurred on Si-O area in the template in an aqueous solution containing SnCl₂•2H₂O of 0.03 M at 60°C. Thin film X-ray diffraction observed that as-deposited film was composed of a cassiterite structure with low crystallinity. The tin precursor hydrolyzed with H₂O molcule and integrated onto Si-O area surface for forming tin oxide thin film. On the other hand, the methyl-terminated group tends to prevent the nucleation from the aqueous solution, because of hydrophilic/hydrophobic anti-interaction. The SnO₂ thin film with high crystallinity had a gas responsibility to the mixture gas containing H₂ of 1.0 vol%.

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GdBa₂Cu₃O_7-δ-based composite ceramics with various BaAl₂O₄ contents were prepared by solid-state reaction. From the elemental maps of Al and Cu measured using an electron probe microanalyzer, BaAl₂O₄ grains were clearly distinguished from GdBa₂Cu₃O_7-δ grains. When a certain voltage was applied to the composite rod electric current decreased abruptly, and a hot spot appeared in the rod. After the appearance of the hot spot, the current remained constant with increasing voltage. The electric power required to melt the rod significantly increased upon adding BaAl₂O₄. The current after the appearance of the hot spot depended on the oxygen partial pressure in the ambient atmosphere. Compared with the GdBa₂Cu₃O_7-δ rod, the composite rod showed high durability for sensing applications even in high oxygen partial pressure. The results revealed that the BaAl₂O₄-added GdBa₂Cu₃O_7-δ composite ceramics is a promising material for use as an oxygen sensor exploiting the hot spot.

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In order to control the affinity control of inorganic/organic hybrids toward a molecule for the application to sensors, the solid acid-base properties of inorganic/organic hybrids were generated by the incorporation of inorganic components other than siloxanes. The solid acid-base strength was varied from basic (H₀=9) to acidic (H₀=1) regions by the incorporation of various inorganic components into methylsiloxane-based inorganic/organic hybrid. The basic methylsiloxane-based inorganic/organic hybrid containing a Ca inorganic component tended to adsorb an acidic molecule of NO₂ and the acidic methylsiloxane-based inorganic/organic hybrid containing a Ti inorganic component tended to adsorb a basic molecule of pyridine. The Al-containing methylsiloxane-based inorganic/organic hybrid with acid-base strength between the Ti- and Ca-containing hybrids adsorbed both a basic molecule of pyridine and an acidic molecule of NO₂. On the basis of the affinity control by verify the solid acid-base strength, the inorganic component derived from Nb(OC₂H₅)₅ was incorporated into the aminopropylsilane-based inorganic/organic hybrid to weaken the strong basicity resulting from amino groups. The aminopropylsiloxane-based inorganic/organic hybrid containing an Nb inorganic component resulted in a detectable change in the optical properties and acted as a reversible sensitive film toward NO₂ for an optical sensor.

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Nano-sized silver particles-deposited silicas were prepared by (a) the sol-gel method, the evaporation-condensation of silver on (b) silica glass and (c) sol-gel derived silica film. Optical absorption peak due to surface plasmon resonance (SPR) of silver particles was measured using UV-VIS spectrophotometer. When the films were immersed in liquid, SPR absorption peak of the films (b) and (c) was shifted toward longer wavelength with the increase of the refractive index of the liquid, suggesting that these films can be used as optical sensors. On the other hand, SPR absorption peak of the film (a) was little shifted. The sensitivity to the refractive index change for the film (b) was 81.4 nm, and that of the film (c) made by depositing silver particles on the sol-gel silica was large as 90.2 nm, which may be attributed to less coverage of silver particles with silica matrix than the film (a) and less aggregate of them than the film (b).

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The influence of Stearic Acid (SA) buffer layer on the durability and sensitivity of an optically readable H₂ gas sensor using Pd film was investigated. The SA was deposited on a glass substrate by vacuum evaporation apparatus. The Pd film was deposited on a glass and the SA/glass substrate by r.f. magnetron sputtering technique. Blister formation of Pd film was remarkably suppressed by using SA thin film as a buffer layer. The Pd/SA films showed a high durability and sensitivity even after repeated hydrogen detection.

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A hot spot, which is a local area glowing orange, appears in a LnBa₂Cu₃O_7-δ (Ln: rare earth element) ceramic rod when a voltage exceeding a certain value is applied to the rod at room temperature. The rod with the hot spot shows various functional characteristics that give rise to applications in devices such as a constant-current generator, an oxygen sensor, a flowmeter and a low-frequency oscillator. In this paper, general features of the hot spot and various applications are reviewed. The hot spot is considered to appear in ceramics with a positive temperature coefficient of resistivity. New application fields may be created from the related researches.

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A hot spot, a local area with high temperature, appeared in a SmBa₂Cu₃O_7-δ ceramic rod when a dc voltage above the threshold was applied at room temperature. Under low oxygen partial pressure, a damped sinusoidal oscillation in the electrical current was observed after the appearance of the hot spot. The frequency of the current oscillation was found to increase when the thermal conductivity of ambient gas increased. The current oscillation associated with the hot spot is expected to be applicable to a variable low-frequency oscillator.

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We have successfully prepared plate-like fine powder of high-Tc phase (2223) superconducting oxide with preferential 002 faces by grinding in dehydrated pure ethanol. In the current study, we attempted quick fabrication of highly oriented (Bi, Pb)₂Sr₂Ca₂Cu₃O_x superconductor using plate-like seed crystals. It was found that the addition of the seed to the commercial precursor (Dowa Kogyo) brought about a considerable reduction in fabrication time. Almost all single phase (2223) sintered superconducting oxide was obtained by heating the precursor mixed with 30 wt% seed for 4 h at 870°C. Furthermore, the grains of the sintered disk were highly oriented.

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The phase transformation of REBa₂Cu₃O_7-x (RE=Nd, Gd, Dy) was investigated using isothermal heat-treatment and continuous cooling in air. During continuous cooling, the REBa₂Cu₃O_7-x (RE-123) superconducting phase with well-distributed RE₂Ba₁Cu₁O₅ (RE-211) was obtained at the cooling rate of 0.001°C/s. Single phase of RE-123 (Nd, Gd, Dy) was stable at 1050°C, 1000°C, and 950°C during isothermal heat-treatment, respectively. Above these temperatures RE-211 phase existed within the RE-123 grains. The RE-123, RE-211, BaCu₂O₂, and CuO phases coexisted at 50°C below the partial melting temperature for each respective RE-123. The variations in the phase transformation and microstructure change on rare-earth elements were explained by the different ionic radii of the elements. The superconducting properties of each specimen heat-treated under the optimum conditions were compared with the magnetic characteristics.

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Composite ceramic rods of GdBa₂Cu₃O_7-δ with BaZrO₃ were prepared by solid-state reaction. A hot spot appeared in the rod when a certain voltage was applied at room temperature. The durability of the rod with hot spot was evaluated by measuring the stability of the current under Po₂=100 kPa. The results show that composite ceramics of GdBa₂Cu₃O_7-δ with BaZrO₃ has a high electrical stability for applying a hot spot compared with GdBa₂Cu₃O_7-δ ceramics.

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We review the single-crystalline film growth techniques for transparent oxide semiconductors including ITO, NiO:Li, InGaO₃(ZnO)_m and LaCuOS on single-crystalline YSZ substrates. Single-crystalline ITO films were grown by a PLD method at 900°C, whereas those of NiO:Li, InGaO₃(ZnO)_m and LaCuOS were not obtained by a simple PLD process. Their chemical compositions are difficult to control because high vapor pressure elements evaporate much faster than lower vapor pressure elements. Thus, we used a solid-phase epitaxy, where polycrystalline epitaxial films deposited at room temperature were converted to single-crystalline by thermal annealing. It successfully led to the formation of single-crystalline NiO:Li films. In reactive solid-phase epitaxy (R-SPE) for InGaO₃(ZnO)_m and LaCuOS, it is necessary, in addition to the thermal anneal, to form an epitaxial template layer before the film deposition. As the layers subsequently deposited on a template layer are amorphous or polycrystalline, chemical composition of the epitaxial films can be controlled.

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Rechargeable lithium batteries with carbon anode and LiCoO₂ cathode have been widely used in our daily life for more than ten years. In order to obtain higher battery performance to meet growing demand in modern technology fields, a variety of alternative insertion materials have been under investigation and a new breakthrough in Li-ion technology is expected. In this article, potential anode materials, especially non-carbon active materials, are described in connection with the lithium storage capability, reaction mechanism and structure stability to lithiation and de-lithiation. Close attention is paid to alloys, compounds and composites containing IVA- and VA-group elements as well as (transition) metal oxides.

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Gadolinium- and samarium-doped ceria powders with compositions Ce_0.8Gd_0.2O_1.9 (GDC) and Ce_0.8Sm_0.2O_1.9 (SDC) were prepared by heating the oxalate solid solution (Ce_0.8R_0.2)₂(C₂O₄)₃ (R: Gd, Sm) at 873 K in air. As-prepared powders with secondary particle size of 0.5-1 μm were densified to 96.6-99.4% relative density by sintering in air at 1773 K for 4 h. The electronic current of disk sample was measured in a temperature range from 773 to 1113 K by direct current polarization method using Hebb-Wagner ion blocking cell. A linear relationship, which was theoretically predicted, was measured between log I (electronic current) and E (applied voltage) for GDC and SDC in the applied voltage range of 0.2-1.4 V. The slopes of log σ (electronic conductivity)-log Po₂ (oxygen partial pressure) plot for GDC agreed with the theoretically predicted value of -1/6. However, the slope for SDC was in the range from -0.10 to -0.16. The transport number of oxide ion for the GDC and SDC was significantly higher than the previously reported values.

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Single crystals of (ZnO)₅In₂O₃ were grown by means of the slow cooling method, using PbF₂ as a flux, at reaction temperatures of 1050-1150°C and different cooling rates. The resulting flaky single crystals with a maximum area of 3×2 mm² were very thin along the c-axis. Single crystal quality was evaluated by XRD, TEM, and SEM. The in-plane electrical conductivity (σ) was measured in the temperature range of 300 K to 1200 K in air. Band gap energy of (ZnO)₅In₂O₃ single crystal was optically determined. Anisotropy of two orders of magnitude in electrical conductivity was first clarified.

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Single-phase polycrystalline samples of γ-Na_0.70Ca_xCoO_2-δ are successfully synthesized in the concentration range, 0≤x≤0.07, by a two-step sintering procedure, i.e., γ-Na_0.70CoO₂ powder mixed with an appropriate amount of Ca(NO₃)₂•4H₂O is sintered at 873 K and 1123 K in air for 12 h. ICP analysis data indicate that Na content (Na/Co=0.64-0.67) is slightly lower than the nominal one (0.70). Oxygen deficiency is determined by the automated iodometric titration technique (δ=0.025-0.033). In this system, formal valence of Co ion linearly decreases from +3.27(2) at x=0 to +3.16(2) at x=0.07, implying electron doping. We have studied thermoelectric properties of γ-Na_0.70Ca_xCoO_2-δ at high temperature. Both electrical resistivity, ρ, and Seebeck coefficient, S, almost linearly increase with increasing temperature. The largest power factor, S²/ρ=6.4×10^-4 W m^-1K^-2 at 985 K, is obtained for the sample with x=0.0175.

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The effects of sintering additives such as Al₂O₃ and Ga₂O₃ on the sintering behavior of gadolinia-doped ceria were systematically investigated in terms of the variations in sintered density and grain size and the existing forms of Al₂O₃ and Ga₂O₃ in CeO₂. Both sintered density and grain size increased with increasing additive content up to 2 mol% for Al₂O₃ addition and up to 5 mol% for Ga₂O₃ addition. However, they decreased with further addition of the additives. At a higher additive content, grain size decreased by a pinning effect of the precipitates at grain boundaries. Lattice constant decreased with increasing additive content up to 2 mol% for Al₂O₃ addition and up to 5 mol% for Ga₂O₃ addition. This decrease will be due to the substitution of smaller Al³⁺ ions or Ga³⁺ ions for Ce⁴⁺ ions in the CeO₂ structure. The solubility limits of additives in Ce_0.8Gd_0.2O_1.9 ceramics estimated using the results obtained from SEM and XRD analyses were about 2 mol% for Al₂O₃ addition and 5 mol% for Ga₂O₃ addition. The addition of Al₂O₃ or Ga₂O₃ up to the solubility limit was found to promote the sintering properties of Gd₂O₃-doped CeO₂.

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A conduction mechanism of Li ions in lanthanum lithium tantalate was investigated by ⁷Li NMR and impedance spectroscopy. Conductivity spectra of La_1/3-xLi_3xTaO₃ with x=0.06 and 0.09 exhibited Jonscher's universal dynamic response behavior. A scaling analysis revealed that the concentration of Li ions responsible for the long-range migration remained constant in the temperature range from -80°C to 30°C. Correlation times for the local motion of Li ions were estimated from the measurement of NMR spin-lattice relaxation times to be in the order of 10^-9 s at room temperature. Activation energies of the correlation times, which correspond to the barrier-height to the elementary hop of Li ions, were 8 kJ mol^-1 for x=0.06 and 10 kJ mol^-1 for x=0.09. These activation energies were confirmed to be related through power-law exponents to those of dc conductivities. In spite of the similar crystal structure and the same Li content, the dc conductivity at room temperature of La_1/3-xLi_3xTaO₃ with x=0.06 was one order of magnitude lower than that of La_2/3-xLi_3xTiO₃ with x=0.06; this may be ascribed to the longer correlation time and the higher activation energy of La_1/3-xLi_3xTaO₃.

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Novel solid-state PEO rechargeable lithium cells based on the LiNi_0.8Co_0.2O₂ cathode and the SnSb-Li_2.6Co_0.4N composite anode have been developed for the high reliability exclusive of metallic lithium and the large energy density at 110 Wh Kg^-1. Electrochemical behavior of the cells demonstrates strong reliance dependent on the anode preparations. In view of the relatively low lithium ion diffusion, current density plays a significantly role upon the capacity and the retention of the composite anode. A cell design with good sealing and compacting configuration, as well as an appropriate thickness of electrolyte and electrode, results in a comparable cycling performance.

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Doped ceria (CeO₂) compounds are fluorite type oxides which show oxide ionic conductivity higher than yttria stabilized zirconia, in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for ‘low (500°-650°C)’ or ‘intermediate (650°-800°C)‘ temperature operation of solid oxide fuel cells (SOFCs). In this study, the authors prepared Gd_xCe_1-xO_2-δ (x=0.1, 0.15, 0.21, and 0.25) and Gd/Sr co-doped CeO₂ [(Gd_0.8Sr_0.2)_0.175Ce_0.825O_1.895] specimens using carbonate co-precipitation method, in order to examine the influence of nano-structural feature on electrolytic properties in the sintered bodies. And the relationship between the microstructural feature in nano-scale and the conducting property in those electrolytes were examined. A diffuse scatter was observed in the background of selected area electron diffraction pattern recorded from all sintered bodies. In addition, all specimens had extra spots in the selected area electron diffraction patterns recorded from sintered bodies. The diffuse scatter means that coherent micro-domain with ordered structure is in the lattice. Extra spots indicate the growth of micro-domain. From the comparison of calculated electron diffraction patterns between fluorite structure and b-type rare earth structure, it is concluded that the structure of micro-domain is distorted b-type rare earth structure or b-type related structure. From the observation of high-resolution transmission electron microscope (HR-TEM), it is concluded that the conducting property in Gd doped CeO₂ and Gd/Sr co-doped systems was strongly influenced by the size of micro-domain with ordered structure. The conductivity in Gd_0.21Ce_0.79O_1.895 sintered body with big micro-domain was lower than that in (Gd_0.8Sr_0.2)_0.175Ce_0.825O_1.895 sintered body with small micro-domain. Therefore, the author concluded that domain control is a key for development of doped CeO₂ electrolytes.

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Pyrolysis of polyvinyl chloride (PVC), in which fine graphite and silicon powders are homogeneously dispersed, produces a new type of silicon/carbon composite host for reversible lithium insertion and extraction. As anode material for lithium ion cells, its cycling capacity reaches about 700 mAh•g^-1 at 0.2 C charging rate. The capacity retention at the 30^th cycle is about 90% against the first cycle, much better than that of pure silicon electrode. A little higher insertion potential of the composites than commercialized Carbonaceous Mesophase Spherules (CMS, similar to MCMB) anode material enhances the charging rate capability and operating safety of the cells. The available capacity is about 450 mAh•g^-1 at 2 C rate for the composite, but it is below 100 mAh•g^-1 for CMS. This paper examines the influence of organic precursors, silicon particle size and current collectors on the electrochemical performance of the composite.

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The thick film resistance systems on LTCC (Low Temperature Co-fired Ceramics) substrates consist of mixtures of Bi₂Ru₂O₇ with pyrochlore structure and have applications in automobile electronics: The resistivity increases linearly with almost no temperature dependence up to a concentration of x=1.5 of rare earth (RE) elements substituting Bi as Bi_2-xRE_xRu₂O₇. Above x=1.5 the increase is much steeper with a strong temperature dependence. With the ab-initio DvXα method the electronic orbitals of electro ceramics can be calculated easily and a new, simple method for estimating the electric conductivity is presented. The comparison between experimental and calculated data showed good correlation, for the Bi-substitution by Rare Earth elements on the A-sites and the Ru-substitution by transition metals on the B-site. This allows the prediction, how the resistivity changes with temperature for doping with elements not yet experimentally observed.

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Molecular dynamics (MD) was used to study ionic conduction processes in mixed valence compound LiMn₂O₄. The evolution of three different Mn valence distribution models was examined. For two models, I and II, the ideal spinel structure was adopted with randomly assigned valences. For model II the Mn valences were periodically randomly altered while preserving overall charge neutrality. In the third simulation, III, a charge ordered Mn valence model resembling the observed low temperature LiMn₂O₄ phase was adopted. Model I reproduces structural characteristics of the ideal spinel well, exhibiting modest Li ion self-diffusion. In model II the Li diffusion was greatly enhanced and in the charge ordered model III almost no diffusion was observed at all. Model II therefore reproduces the observed physical properties of the high temperature cubic spinel phase best, strongly supporting a Mn valence electron hopping model. Structural distortion indices were also calculated confirming that Li diffusion from the ideal tetrahedral LiO₄ environment is strongly associated with tetrahedral distortion.

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High temperature thermoelectric properties of Ca_1-xY_xMnO_2.98 (x=0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) have been measured in the temperature range from 300 to 1273 K. Ca_1-xY_xMnO_2.98 (x=0.05, 0.10, 0.15, 0.20) exhibited the metal-insulator transition (T_t) in the relation between electrical resistivity and temperature, and the transition temperature increased with increasing x content. Electrical resistivity in the metallic region above T_t decreased with increasing x content, reflecting the increase of Mn³⁺ ions. In the semiconductor region below T_t, the band gap increased with increasing the doped x content. The Seebeck coefficients of all samples were negative, and the absolute value of Seebeck coefficient at low temperature decreased with increasing x content. Thermal conductivity decreased with increasing x content due to the increase in phonon scattering by the doped Y ions. Among substituted CaMnO₃, the highest figure of merit of Z=1.77×10^-4 K^-1 was obtained for x=0.15 at 1273 K.

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Hydrogen is a promising candidate for the impurity causing the n-type conductivity in ZnO. In this study hydrogen was introduced into the ZnO specimens by the ion implantation technique. The content of hydrogen was detected by the elastic recoil detection analysis (ERD). According to the ERD measurements, the counts of hydrogen increased after the implantation. The electrical conductivity of the hydrogen-implanted layer increased by about 9 orders of magnitude in case of the most resistive Cu-doped ZnO. The photoluminescence (PL) spectra for the Cu-doped ZnO were also measured, and the PL emission peak around 520 nm disappeared after the hydrogen ion implantation. The mechanism for such a hydrogen effect on the electrical conductivity of ZnO was discussed on the basis of the PL spectra and the DV-Xa molecular orbital calculation.

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Porous conductive glass was designed and prepared by depositing transparent conductive film (TCF) on inner surface of pores and outer surface of porous glass (PG) with nano-size pores. In the present study, tin oxide (SnO₂) was deposited onto the inner surface of PG pores to form a nanocomposite first by using chemical vapor deposition (CVD) method. TCF of SnO₂ or indium tin oxide (ITO) was then deposited onto the outer surface of the nanocomposite by using spray pyrolysis deposition, laser ablation (LA) and CVD methods. Surface area of obtained porous conductive glass is about 10⁵ times more than that of flat dense TCF. The obtained samples are translucent due to the scattering of light. This kind of porous conductive glass is expected to provide a huge reactive field for functional materials used in photoelectric devices, which in turn increases devices' function such as light-to-energy conversion efficiency drastically.

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