Low-temperature processing of solution-derived ferroelectric thin films comprises various approaches to decrease the crystallization temperature of the target crystalline phase to the values which would render the films compatible for integration in electronic devices. Beside the solution chemistry, nucleation layers and design of the deposition and heating profile, additional approaches are discussed in the paper. They include activation of amorphous films including UV or photochemical activation, laser activation or microwave heating. Hydrothermal growth of thin films is also discussed.

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Si₂N₂O powder was synthesized by the direct reaction of silicon and silicon dioxide in an N₂ atmosphere at 1450°C; the resulting Si₂N₂O powder was doped with Eu in a H₂/N₂ atmosphere at 1350°C. The Eu-doped SrSi₂O₂N₂ powder showed a phosphorescence peak at approximately 530 nm with an excitation wavelength of 450 nm. Increasing the Eu content in the Eu_xSr_1−xSi₂O₂N₂ (x = 0–0.15) phosphor red-shifted the peak position. The Eu_0.01Sr_0.99Si₂O₂N₂ phosphor showed high durability in water, and the emission intensity of the Eu_0.01Sr_0.99Si₂O₂N₂ phosphor after soaking in water was 1.2 times higher than that of the phosphor before soaking in water.

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We investigated a novel simple method to synthesize CaNb₂O₆ from precursors formed in immiscible liquid–liquid biphasic systems. Niobium pentaethoxide and calcium acetate monohydrate were used as starting materials, which were dissolved separately in hexane and water, respectively. After putting the hexane solution on the aqueous solution, they started to react at the interface of the two liquid phases and then a mixture of calcium acetate and amorphous niobate gels was precipitated in the aqueous solution at room temperature. The precipitates could be transformed to CaNb₂O₆ by heating at 700°C for 30 min. The morphology of the CaNb₂O₆ sample was characterized as rough and dimpled spheres 400–500 nm in size. The sample exhibited a blue emission upon excitation with ultraviolet light. A comparative study using a one-phase liquid method or a solid-state reaction method has strongly suggested that the biphasic liquid method is advantageous for obtaining highly luminescent CaNb₂O₆ at the lower processing temperatures.

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SrAlSiN₃:Eu²⁺ is a red-emitting phosphor that is potentially very useful in white light-emitting diodes because of its properties such as thermal stability and bright emissivity features. A limitation of this phosphor is that it is commonly synthesized at high temperature (2173 K) and pressure (190 MPa). To address this limitation, we report (1) a low-temperature (1073 K) synthesis of SrAlSiN₃:Eu²⁺ phosphors through a dissolution–precipitation process in supercritical ammonia (ammonothermal method) and (2) an investigation of the phosphors’ physical properties. All products exhibit a broad emission that is centered at approximately 580 nm, which we attribute to the 5d→4f transition of Eu²⁺, under excitation wavelengths from the ultraviolet to blue range. We used Sr as a mineralizer to synthesize a superior product in terms of a high Sr concentration in the crystals, improved crystallinity, and enhanced emission intensity.

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Polycrystalline plate-like TiO₂ specimens were irradiated with a continuous-wave Yb-fiber laser, and the electrical properties of the modified layers were investigated. The irradiated part was modified in color and electrical properties when the laser power was set above a certain threshold. The color changed from white to black, and the electrical resistivity drastically decreased from an initial value of 3.3 × 10⁹ Ω cm to 1.9 Ω cm at 2.0 W. The Hall measurement showed that the modified layer was an n-type semiconductor, and the carrier concentration was 3.6 × 10¹⁷ cm⁻³ at 2.0 W.

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Phosphorus doped WO₃ (P_xW_1−xO₃) ceramics were fabricated by a solid state reaction. Temperature and frequency dependence of dielectric properties for the P_xW_1−xO₃ (x = 0–0.15) ceramics were evaluated at the temperature between −20 to 80°C. The dielectric constant of the P_0.05W_0.95O₃ ceramic was 3600–5800 at the frequency range from 1 kHz to 1 MHz in the room temperature, and the dielectric loss of the P_0.05W_0.95O₃ ceramic were less than 0.1 at the frequency of higher than 160 kHz. The dielectric anomaly peak of the WO₃ ceramic has been observed at 20°C, and the dielectric anomaly peak of the P_0.05W_0.95O₃ ceramic has been observed at about 0°C. The interaction between temperature dependence of dielectric properties (dielectric anomaly) ceramics and structural change of the WO₃ and P_0.05W_0.95O₃ were evaluated by Raman spectra.

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The ferrite-silica aerogel nanocomposite prepared by a sol–gel process and a supercritical drying process was investigated from the point of view of new composite material. The ferrite nanoparticles were prepared by a coprecipitation method and added to tetramethylorthosilicate (TMOS) in the range of 0 to 20 mol %. The ferrite-silica wet gel was prepared from TMOS containing ferrite nanoparticles, ethanol, deionized water and NH₃ aq. as a catalyst, and replaced the liquid phase and aged in the ethanol. Then, a hydrophobing treatment was performed in hexamethyldisilazane toluene solution. Finally, the ferrite-silica wet gel was dried in the supercritical carbon dioxide fluid. The obtained ferrite-silica aerogel nanocomposite was evaluated by bulk density, porosity, specific surface area, pore size distribution, SEM and TEM observation, EDS analysis and magnetization measurement by VSM. As a result, even if it added the ferrite, the characteristics of aerogel was held and the magnetic property of the ferrite remained unchanged in the aerogel.

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Nano-sized Y₃Fe₅O₁₂–nSmFeO₃ mixed powder (ca. 20 nm in particle size) was prepared by bead-milling using 0.05 mmφ beads for 10 h. For the SmFeO₃-free sample (n = 0), the heat generation ability in an AC magnetic field (370 kHz, 1.77 kA·m⁻¹) was 0.34 W·g⁻¹ for the bead-milled sample, and it was increased by a calcination at low temperature. The maximum ability of 0.46 W·g⁻¹ in an AC magnetic field (370 kHz, 1.77 kA·m⁻¹) was obtained for the Y₃Fe₅O₁₂ (n = 0) sample (36.8 nm in particle size) calcined at 700°C. The heat generation mechanism changed from superparamagnetic to ferrimagnetic due to particle growth at 700°C for the n = 0 sample, because the heat generation ability (W·g⁻¹) depended on the cube of the magnetic field. A mixed SmFeO₃ phase acted as an impurity for depression of the particle growth for the Y₃Fe₅O₁₂ particles. The heat generation ability was slightly improved by the addition of SmFeO₃ and the maximum value was 0.48 W·g⁻¹ in an AC magnetic field (370 kHz, 1.77 kA·m⁻¹) for n = 0.2 and 0.4 samples. The maximum heat generation ability was decreased for the excessive SmFeO₃ mixed sample (n = 0.6). The calcination temperature for the formation of the ferrimagnetic material was increased by the SmFeO₃ addition due to the depression of particle growth.

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In order to apply for magneto-optical (MO) devices, the thermally non-equilibrium Bi₃Fe₅O₁₂ (BIG) films have been investigated. The films were prepared by metal organic decomposition (MOD) technique. The BIG thick film prepared in our previous processing showed the low Faraday rotation which was the same performance of the film with 300 nm. According to our previous preparation process, the crystallization from the amorphous phase to the garnet phase by post annealing was achieved after final spin-coating. We modified the process and repeated the post annealing process after every 5 times coating, then we obtained the thick film with high MO performance. The XRD analysis showed cube on cube crystal growth of the film on the substrate. The Faraday rotation of the film increased in proportion to the thickness of the film. The saturation magnetization was approximately 150 mT. The ferromagnetic resonance indicated the in-plane magnetic anisotropy. The microstructure of the cross section of the film revealed some damage at the interface area between the film and the substrate, which suggests more improvement of the annealing process. However, the BIG thick film prepared by MOD technique has high MO performance for the application for the optical devices.

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Catalysts based on Zr–O material were prepared from zirconium oxychloride and zirconium oxynitrate with ultrasonication. The deposited Zr–O materials were not detected by XRD because of amorphous phase of an oxygen deficient type zirconia. The obtained zirconia based composite showed higher catalytic performance for oxygen addition activity than Pd based composite for the combustion of carbon. However, the obtained zirconia based composite showed the less catalytic performance for dehydrogenation reaction activity than Pd based composite for the combustion of methane. This zirconia based catalyst is expected to use for the electrode material of the fuel cell that needs restraint of the carbon deposition.

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The Fe₃O₄ particles were prepared from iron chloride by the hydrothermal reaction. The resultant Fe₃O₄ particles possessed good crystalinity when using the NH₄OH precipitant and showed the high saturated magnetization value of ca. 90 emu/g. Resin compacts including above ferrite powders were prepared using a centrifugal molding technique. The resultant concentration-gradient resin composites exhibited better broadband electromagnetic wave absorption than the homogeneous resin compacts (no gradation). Such absorption ability is responsible for the suppression of undesirable reflection on the incidence plane and effective thermal loss transducing of electromagnetic wave near the reflector where the magnetic powders are condensed.

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An aqueous solution of aluminum nitrate and yttrium nitrate was prepared and ethylenediamine molecules were added into the aqueous solution. The obtained precipitated precursor particles were fired and oxide particles were obtained. When ethylenediamine was used for the precipitation, the single phase of YAG was obtained by firing the precursor particles at more than 1073 K. On the other hand, when hexamethylenediamine was used for the precipitation, the YAG phase was not able to obtained by firing the precursor at 1373 K. Formation behavior of YAG phase greatly depended on the used diamine molecules. Furthermore, Ce³⁺-doped YAG particles were prepared by firing precipitated particles from the aqueous solution in which the nitrates of Al³⁺, Y³⁺, and Ce³⁺ were dissolved with ethylenediamine as precipitating agent. The PL spectra of the obtained particles had the photoluminescence (PL) peak at 535 nm even though the firing temperature was 1073 K.

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Grain-oriented Nd-modified bismuth titanate (BNIT) ceramics with the a-b-plane perpendicular to the direction of magnetic field (MF) were successfully fabricated by applying MF-assisted forming at lower field strengths. A BNIT powder, in which 25% of the Bi³⁺-site were substituted with Nd³⁺, was synthesized by coprecipitation in an alkaline solution and successive calcination at 600°C. Green compacts of the BNIT powder were formed by applying various MF strengths (2–12 T) during slip casting and then sintered at 900 and 1000°C for different times. The cation substitution with Nd³⁺ allowed very fine BNIT particles in a slurry to be magnetically aligned at lower field strengths. For BNIT ceramics sintered at 1000°C, the degree of grain orientation increased with increasing MF according to the parabolic relationship. Additionally, the grain orientation was enhanced by the preferential growth of anisotropic BNIT grains occurring at later stage of the sintering.

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The precursor solution for lanthanum strontium cobalt oxide (LSCO) was modified to increase the single-layer film thickness. Results show that LSCO with 170 nm thickness was deposited on a Si wafer for stress engineering of a ferroelectric thin film. The single-layer film thickness for LSCO layer increased concomitantly with increasing viscosity in LSCO precursor solution. In addition, the crystallinity and the electrical resistivity of a LSCO with lanthanum nickel oxide (LNO) seeding layers using the modified LSCO precursor solution was nearly equal to that of the reported LSCO precursor solution. The residual stress in lead zirconate titanate with Zr/Ti = 53/47 composition thin film on a LSCO(170 nm)/LNO(160 nm)/Si stacking structure was −0.9 GPa compressive stress, which enhances the ferroelectric property (2P_r = 120 µC/cm²).

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A relative dielectric constant of a solvent is important for the electrophoretic deposition (EPD) suspension, and when the electrical resistance of the solvent is high, a large quantity of material is expected to be deposited. In this study, ethylperfluorobutylether (EFE), which is a kind of hydrofluoroether, was applied as the solvent for preparing a particle suspension for the EPD. EFE has the advantages of being polar, non-flammable, and having high electrical insulation properties. Silica powder was selected as the deposition material. When EFE is used, unlike when acetone-based EPD suspension was used, the amount deposited remains the same, but power consumption is 1/2,000 or less. Depending on conditions, power consumption is reducible even to 1/200,000. Thus, highly efficient EPD with ultra power saving ability was achieved. In addition, this process is extremely safe as EFE is non-flammable, removing the hazard of ignition. As the specific gravity of EFE is large, sedimentation of inorganic particles is slow; therefore, the dispersibility is excellent, and highly uniform coatings can be obtained. Unlike water-based EPD suspensions, the application of a high voltage is possible. In the present study, the deposition behavior was no different from that for conventional EPD, being controllable by varying the applied voltage, deposition time, and particle concentration.

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This study elucidated the effects of coherence of grain boundary of 6 mol % Y₂O₃-doped ZrO₂ (YSZ) thin films on ionic conductivity. The YSZ thin films were deposited with several orientation textures on MgO (100) and Al₂O₃ (102) substrates using metal–organic chemical vapor deposition (MOCVD). Impedance measurements revealed that the total ionic conductivity of the thin films was restricted by the columnar grain boundary. The orientation degree, defined by the average full width at half maximum (FWHM) of 100 pole of the YSZ thin films, mainly determines the ionic conductivity across the columnar grain boundary because of the degree of the crystallographic coherence. Films with a strongly oriented columnar structure showed ionic conductivity of about 30 times higher than that of nanocrystalline films having random orientation. The activation energy of the ionic conduction across the columnar grain boundaries simply increased concomitantly with decreasing degree of orientation of the columnar grains of the films. HRTEM analyses revealed that the small tilt angle grain boundary with low lattice defect density and with no second phase at grain boundaries showed superior properties. Consequently, a columnar structure with high coherence is preferred for use as a thin film ionic conductor.

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The cubic Li₄Ti₅O₁₂ nanoparticles were continuously synthesized in supercritical water using a flow hydrothermal reaction system. Ti-sols(M-6, A-6) and Ti(SO₄)₂ were used as the Ti source. Initial Li/Ti molar ratio was varied with the LiOH concentrations. The syntheses were carried out at temperatures from 350 to 410°C, at pressure of 30 MPa, and for residence times from 10 to 26 s. X-ray diffraction (XRD), transmission electron microscopy (TEM), BET surface area, and Dynamic light scattering (DLS) technique were used to characterize the samples. Single phase of Li₄Ti₅O₁₂ was achieved under supercritical conditions at initial Li/Ti molar ratio >2.5 from Ti-sol(M-6) and >2 from Ti-sol(A-6), respectively, whereas single phase was not obtained from Ti(SO₄)₂ solution even at initial Li/Ti molar ratio of 10. It requires the pH range over 12 to prepare the single phase Li₄Ti₅O₁₂. As-synthesized samples exhibited the diffuse scattering (111) and missing (311) reflections due to a disorder in Ti–O framework, whereas the presence of these two reflections indicates reordering of the Ti sublattice after annealing.

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MoO₃ based photochromic composite films were fabricated using a Mo-IPA methanol solution and a transparent urethane resin, and the photochromic property of the films was controlled by copper addition. All the composite films colored by UV–vis light irradiation, and bleached in placing a dark room. The initial color of the films changed from blue to transparent by Cu addition to the composite film, and Cu addition caused acceleration of the bleaching speed of the composite films with the Cu/Mo ratio of higher than 0.5.

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We examined the effect of polymer polytetrafluoroethylene (PTFE) additive on the growth of InN crystals by the nitridation of LiInO₂ in NaNH₂ flux at 240°C. LiInO₂ and NaNH₂ powder were heated with/without PTFE pieces in a steel crucible located inside the PTFE-lined autoclave. The additive of PTFE pieces enhanced the decomposition of LiInO₂ with the mass loss of these pieces and progressed the formation of InN and In(OH)₃ byproducts. SEM and TEM images of the products using PTFE additives showed the hexagonal InN crystals of ~1 µm in size, and the optical bandgap of synthesized InN was estimated as ~2.03 eV. We presume that fluorine in PTFE additive subtracts Li from LiInO₂ and enhances the growth of InN crystals.

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The photoluminescence properties of 0.2% Pr³⁺-doped (Y_1–0.01xZr_0.01x)₂O₃, (x = 0, 0.1, 1, 3, 4.5, 6) ceramics were investigated. The luminescence intensity due to the transition from the ³P₀ level increased drastically when the Zr content x increased, which is completely quenched in Y₂O₃:Pr³⁺ (x = 0) due to the thermal relaxation through the lowest 5d level of the Pr³⁺ ion. By monitoring at 630 nm (¹D₂→³H₄), we found that the 4f–5d photoluminescence excitation bands for Pr³⁺ in the two six-fold sites [C₂ and S₆ in the Y₂O₃:Pr³⁺ (x = 0)] were observed at approximately 300 and 340 nm. On the other hand, when monitored at 510 nm (³P₀→³H₄), the Zr-doped samples showed an additional 4f–5d band at 280 nm. Based on these results, we concluded that the ³P₀ luminescence is from Pr³⁺ in a seven-fold site, which is generated by incorporation of an additional oxygen via a defect chemical reaction, $2\text{ZrO}_2 \xrightarrow{\text{Y}_2 \text{O}_3} 2\text{Zr}_\text{Y}^ \bullet + \text{O}_\text{i}^{\text{\prime\prime}} + 3\text{O}_\text{O}^\text{x} $.

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The fundamental equation of the rate of hydration derived by Tomozawa, which was originally applied to a single particle, was applied to the hydration process of Portland cement using a size distribution function. We generalized the fundamental equation to apply it to particle size distribution system. Actually, multiple reaction rates that vary according to the particle size can be superposed under a common axis of reaction time using an infinite series of Bessel polynomials as a function of the reaction time. By simulating the heat liberation with the hydration rate equation in terms of the size distribution, the parameters in the equation could be accurately determined.

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The responses of SnO₂ and ZnO were investigated to several atmospheres via optical and electric approaches. Optical absorption spectroscopy was adopted to detect the formation of the defect levels in the energy-band-gaps by the reducing treatments, while the changes in the electric properties of the materials were evaluated by Hall effect measurements. The electric measurements revealed that the response of the SnO₂ films to 0.5% H₂/N₂ consisted of two components. One was steep rise of the electric conductance as the films were exposed to the gas, and the second was gradual increase after the conductance jump, which lasted for several hours until reaching a plateau. The SnO₂ films after reaching the plateau exhibited the enhancement of optical absorption between 340 and 800 nm and it was attributed to the formation of oxygen vacancies by the reducing treatment. The Hall effect measurements revealed that the increase of the electric conductivity of the SnO₂ films was a consequence of increase of both the carrier concentration and the mobility. On the other hand, a change of the optical absorption was not observed for ZnO and Al-doped ZnO films against 0.5% H₂/N₂ up to the treatment temperature of 400°C. The Al–ZnO films showed the carrier concentration dependence in the responses. When Al was doped in ZnO to enhance the carrier concentration at a relatively low level (~10¹⁹ cm⁻³), the change of the electric conductivity according to the atmosphere did follow the change of the mobility. As the carrier concentration increased to ~10²¹ cm⁻³ with higher Al doping, the response became dominantly influenced by the change of the carrier-concentration according to the atmosphere. Even though SnO₂ and ZnO are both typical semiconductive oxides, the interaction with the atmospheres is different from each other.

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We tried to synthesize FAU zeolite from alumonoborosilicate glass used in liquid crystal displays, of which the discard volume is supposed to increase in the near future. The effect of hydrothermal process factor on the synthesis of FAU zeolite using aluminoborosilicate glass, which is poorly alkaline-soluble, was investigated. From X-ray diffraction, with increasing aging time before hydrothermal treatment, the production of FAU zeolite increased, whereas, that of zeolite P decreased. From inductively coupled plasma atomic emission spectrometry, the concentration of Si in the solution increased and that of Al decreased during aging. This indicates that aluminosilicate was generated from Si from aluminoborosilicate glass and Al from sodium aluminate. With aging time, generated aluminosilicate was aged, resulting in preferential synthesis of FAU zeolite. From scanning electron microscopy, increasing aging time resulted in a small crystal particle size of the synthesized FAU zeolite. At higher aging temperature than room temperature, the dissolution of aluminoborosilicate glass was accelerated, zeolite P increased. When NaOH concentration of aqueous solution decreased, zeolite A was synthesized. This indicates that aluminoborosilicate glass did not elute substantially, therefore low silica zeolite was generated. At higher NaOH concentration, FAU zeolite was generated because Na⁺ ion stabilized FAU zeolite and more Si eluted from aluminoborosilicate glass. Zeolite P which is a stable phase was generated when hydrothermal treatment temperature was high and treatment time became long. From nitrogen adsorption/desorption measurements, the microstructure of the obtained product was almost the same as the pure FAU zeolite. We clarified the potential of aluminoborosilicate glass as a starting material of FAU zeolite, widely used in catalysts, adsorbents, gas separation agents and so on.

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The aerosol deposition method (ADM) is a technique to form dense films by impacting solid particles on a substrate. Dense ceramic films with thicknesses of over several µm can be formed directly on substrates even at room temperature by the ADM. In this study, to improve the deposition efficiency of the ADM, the effect of the process for producing Al₂O₃ particles on the deposition efficiency was investigated. Two types of commercially available α-Al₂O₃ particles produced by sintering Al(OH)₃ (sintered particle) and chemical vapor deposition (CVD particle) were used. The average deposition efficiency of the sintered particles ranged from 0.067 to 0.088% and was much higher than that of the CVD particles, which ranged from 0.005 to 0.012%. When the sintered particles were used, the AD films grew about 30 µm. In contrast, when the CVD particles were used, the AD films didn’t grow over several µm. The morphologies of the AD films suggested that the deformed volume of the sintered particles was larger than that of the CVD particles. The specific fracture energy of each particle was estimated from a compression test. The average specific fracture energy of the sintered particles was 7.3 × 10⁷ J/m³, which was about 32% of that of the CVD particles (2.3 × 10⁸ J/m³). Comparing this specific fracture energy with the specific kinetic energy, which was estimated to range from 4.4 × 10⁷ to 1.8 × 10⁸ J/m³, there is a possibility that the sintered particles showed higher deposition efficiency because they could deform by their kinetic energy and easily form activated surface promoting the bonding between the ceramic particles. We conclude that the specific fracture energy of the particle depends on the process for producing it and could be the crucial property to focus on to improve the deposition efficiency.

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High-quality x[(Mg_0.6Zn_0.4)_0.95Co_0.05]₂TiO₄–(1 − x)Ca_0.8Sr₂TiO₃ ceramics were prepared by solid-state reaction. The products were characterized by scanning electron microscopy, X-ray diffraction, and network analyzer. [(Mg_0.5Zn_0.5)_0.95Co_0.05]₂TiO₄ has a dielectric constant (ε_r) of ~18, a high quality factor (Q × f) of ~206,000 GHz, and a temperature coefficient of resonant frequency (τ_f) of ~−20.8 ppm/°C. To produce a temperature-stable material, Ca_0.8Sr_0.2TiO₃, which has a large positive τ_f value of 400 ppm/°C, was added to [(Mg_0.5Zn_0.5)_0.95Co_0.05]₂TiO₄. 0.93[(Mg_0.5Zn_0.5)_0.95Co_0.05]₂TiO₄ –0.07Ca_0.8Sr_0.2TiO₃ has an excellent combination of microwave dielectric properties: ε_r ~18.24, Q × f ~130,000 (at 9 GHz), and τ_f ~1 ppm/°C sinter at 1175°C, and can be utilized in the fabrication of microwave devices. Therefore, a band-pass filter is designed and simulated using the proposed dielectric to study its performance.

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New types of calcium phosphate glass-ceramics were prepared with the addition of Nb₂O₅ to the pyrophosphate region. The glass-ceramics contained α-Ca₂P₂O₇, β-Ca₂P₂O₇, and orthorhombic Nb₂O₅. The concentrations of Ca, P and Nb elements released from the glass-ceramics were lower than those released from glass of the same chemical composition. Apatite formed on the surface of the glass-ceramics after soaking in 1.5 simulated body fluid for 7 days. The crystal phases of the glass-ceramics improved the chemical durability and apatite forming ability of the material.

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