Epitaxial growth of oxide films at lower temperatures is favored to obtain sharp interfaces and flat surfaces which are of advantage to construct high-quality electronic devices, and also is expected to result in novel development of unequilibrium structure and new electronic functionalization. Pulsed laser deposition (PLD) technique using laser ablation of a solid target is known to reduce the temperature drastically for epitaxial growth because of the highly energetic film precursors ablated from the target. In this article we briefly review the main achievements of our research group on room-temperature (RT, 20°C) synthesis of epitaxial oxide thin films by way of laser MBE process, i.e. PLD in ultrahigh vacuum. RT-epitaxial film growth by laser MBE and its electronic application were presented for some functional oxide thin films such as ZnO, Sn-doped In₂O₃ (ITO), sapphire (α-Al₂O₃), (Li,Ni)O, or (Mg,Ni)O, and also magnetic functionalization via selective post-depositional reduction of complex oxide films was demonstrated.

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SmNiO₃ (SNO) films were fabricated on quartz substrates by a spin coating method using Sm–Ni based aqueous solution. SNO film annealed at 700°C showed low crystallinity, while film annealed at 800°C showed high crystallinity. The transmittance of these films did not vary above or below the transition temperature of SNO. SNO films were also fabricated on an SNO seeding layer, with crystalline SNO film obtained at an annealing temperature of 700°C. The transmittance of the resulting film changed above and below the transition temperature of SNO.

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A superparamagnetic magnetic Y₃Fe₅O₁₂ ferrite of 20.5 nm in particle size was prepared by bead milling using 0.05 mmφ beads for 10 h. 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 was improved by calcination at low temperature. The main reason for this heat generation property of the milled samples was ascribed to a Néel relaxation of the superparamagnetic material. 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 sample (36.8 nm in particle size) calcined at 700°C. The heat generation ability was decreased with particle growth when the calcination temperature was higher than 700°C. For the sample calcined at 600°C, the heat generation ability (W·g⁻¹) was proportional to the square of the magnetic field (H/kA·m⁻¹). In the case of the calcination at 700°C, the heat generation ability (W·g⁻¹) depended on the cube of the magnetic field. The heat generation mechanism would change from superparamagnetic to ferrimagnetic due to the pariticle growth at 700°C.

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Composite films with an array of needle like TiO₂ particles in urethane resin matrix were fabricated by applying AC bias. The resulting composite films showed angular dependence of transmittance in the visible-NIR wavelength range. The angular dependence of transmittance of the film increased with the increase in the aspect ratio of the TiO₂ particles. The composite films using needle like TiO₂ particles with an aspect ratio of 19 indicated that the transmittance changed by 25.4% between 0 and 60° at a wavelength of 500 nm.

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A heteronuclear (NH₄)₂Sr[Fe^II(CN)₆] complex having a tetragonal phase was synthesized from Sr(NO₃)₂ and (NH₄)₄[Fe^II(CN)₆]·nH₂O. A single phase of the heteronuclear (NH₄)_2XLa_1−XSr_X[Fe(CN)₆]·nH₂O complex was synthesized by the coprecipitation for two heteronuclear hexacyano complexes of La[Fe^III(CN)₆]·5H₂O and (NH₄)₂Sr[Fe^II(CN)₆]. In this chemical method, the X value (Sr content) for the complex was lower than that of the starting material. This (NH₄)_2XLa_1−XSr_X[Fe(CN)₆]·nH₂O complex was also obtained by a mechanochemical reaction using a planetary ball-mill for two complexes (Total 0.01 mol = ca. 4 g) of (1 − X)La[Fe^III(CN)₆]·5H₂O and X(NH₄)₂Sr[Fe^II(CN)₆] with a small amount (5 ml) of methanol. The hydration number calculated from the elemental analysis agreed with the estimated values when a hexagonal single (NH₄)_0.8La_0.6Sr_0.4[Fe(CN)₆]·4.2H₂O phase formed for X = 0.4. This reaction for X = 0.4 was also possible for the dry process without methanol. In the case of X > 0.4, the peaks of the SrFe- complex were observed in the XRD pattern. The perovskite phase was directly formed by the thermal decomposition at a low temperature for the milled X = 0.4 complex.

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In the equilibrium state, although ZnFe₂O₄ is paramagnetic, it is known that its magnetic property can be modified under nonequilibrium perturbations such as rapid cooling. Ultrasonic spray pyrolysis is a kinetic process involving rapid cooling. In this work, ferrimagnetic ZnFe₂O₄ particles were synthesized successfully. Furthermore, by changing the carrier gas, p-type and n-type ZnFe₂O₄ particles were synthesized. The p-type ZnFe₂O₄ showed low photocatalytic activity, but n-type ZnFe₂O₄ showed considerably strong activity against UV light. Recently, synthesis of magnetically separable photocatalyst has been developed with hybrid or composite of ferrite and TiO₂. The fact that our ZnFe₂O₄ particles show both ferrimagnetic and photocatalytic properties indicates that this material will present new vistas as a magnetically separable photocatalyst.

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One of the calcium aluminate, 12CaO·7Al₂O₃, was synthesized from calcium sulfite hemihydrate waste which was produced as a by-product of calcium polysulfide. The calcium sulfite waste was at first pre-treated by sodium salts, Na₂CO₃ and Na₂C₂O₄. Then, the waste was converted to the CaCO₃ and CaC₂O₄, respectively. From these pre-treated sample, 12CaO·7Al₂O₃ phase was formed at 850°C for the converted CaCO₃ from Na₂CO₃ and at 650°C for the converted CaC₂O₄ from Na₂C₂O₄. These crystallization temperatures are much lower than from reagent CaCO₃ and CaC₂O₄ at 1250 and 850°C, respectively. The reason of such reduction of crystallized temperature may result from impurity Fe₂O₃ including in the by-product. Actually, addition of Fe₂O₃ into the reagent CaCO₃ posed decrease of crystallization temperature of 12CaO·7Al₂O₃ from 1250 to 1050°C.

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The interest in the soft magnetic nano-composite films has grown to realize down-sized microelectronic devices at GHz frequency. In this study, the good soft magnetic Co–TiN nano-composite films were successfully prepared at room temperature (RT) by a sputtering method. XPS results prove that the Co in the films is pure metallic state. The nano-composite films show good frequency response of permeability, which resonance frequency is as high as 1.3 GHz. The films have high magnetic loss absorption (P_loss/P_in) around 1.5 GHz range, which have a high potential for noise suppressors in high frequency devices.

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The dispersion state of boron oxide (B₂O₃) and carbon components in a precursor prepared from a condensed boric acid (H₃BO₃)-polyol product by thermal decomposition in air was found to be closely related to the formation of boron carbide (B₄C) powder at a low synthesis temperature. The microstructure in the precursor was fabricated by controlling the composition of a condensed H₃BO₃-poly(vinyl alcohol) (PVA) product. The size of B₂O₃ particles dispersed in the carbon matrix of the microstructure decreased with increasing PVA content of the condensed product. Crystalline B₄C powder with a little free carbon was synthesized from a precursor with a more finely and homogeneously dispersed structure consisting of B₂O₃ particles and the carbon matrix by heat treatment at 1200°C for 5 h in an Ar flow. Furthermore, the formation and subsequent grain growth of B₄C particles were promoted even at a low synthesis temperature.

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Epitaxial barium hexaferrite [BaFe₁₂O₁₉ (BaM)] thin films were grown on YSZ-buffered Si(001) substrates using a PLD apparatus in which an electromagnet had been installed (dynamic aurora PLD). We examined the effects of applying a magnetic field (up to 2 kG) on the crystal structure and magnetic properties during deposition. The application of the magnetic field during deposition had little effect on the orientation, residual strain, and Curie temperature of BaM thin films. However, the crystallinity and saturation magnetization of the films were lowered. Possible reasons for the lowering of saturation magnetization are discussed.

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Zirconia-cluster/saponite composites were prepared and evaluated as solid acid catalysts. The saponite layer was destructed in the composite through the dissolution of Al ion. The amount of zirconia-cluster in the composites was positively correlated with the Al amount, suggesting that zirconia-cluster inhibits the Al dissolution. Both the amounts of Brønsted and Lewis acids were increased by combining zirconia-cluster to saponite. Results show that Lewis acid on the saponite surface plays an important role on the entire catalytic activity on isomerization of 1-butene. The zirconia-cluster/saponite catalysts provided higher activity with a longer lifetime on this reaction than a commercial montmorillonite-based catalyst.

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NiCuZn ferrite–(Ba_0.7Sr_0.3)TiO₃ (BST) composite ceramics with the BST content of up to 50 vol % were fabricated by sintering compacted powder mixtures at 900°C. The granulation of the BST powder and addition of a Bi₂O₃-based oxide additive effectively assisted the densification of the composite samples. The samples thus fabricated showed required ε_r values whereas their μ_r values were considerably reduced, especially for those with lower BST contents. From the detailed examinations on the effect of the Bi₂O₃-based oxide additives and on the process modification to improve the reduced μ_r values, the addition of a Bi₂O₃–ZnO additive with the eutectic composition of as low as 1 wt % was enough to produce a densified 10 vol % BST composite sample with a highest μ_r value. It was also found that the incorporation of ferrite granules calcined at 600°C caused further improvement of μ_r. Thus, a densified 10BST composite sample with μ_r = 125 was fabricated by low-temperature sintering at 900°C.

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ZnO nanoparticles and their stable sols were prepared by heating an ethylene glycol solution of Zn(NO₃)₂·6H₂O (0.1 mol/L, 50 mL) with 2 mL of NH₃ aq at 328 K for 24 h. The obtained sol contained ZnO nanoparticles with average diameter of around 20 nm. The particle size decreased with increased the concentration of NH₃. Furthermore, the ZnO nanoparticles dispersed in the sols showed a green photoluminescence peak around 550 nm. The heating procedure of the ethylene glycol solution at 328 K yielded stable sols of ZnO nanoparticles with photoluminescence characteristics. In order to control the photoluminescence characteristics of the ZnO nanoparticles, the ethylene glycol solution which contained zinc nitrate hydrate, glucose, and 1 mol/L of NH₃ aq was heated at 328 K for 24 h. The obtained ZnO nanoparticles dispersed in the sols showed a blue photoluminescence peak at around 420 nm. The glucose reacted with Zn²⁺ ions as a reduction agent. Accordingly, the simple one-pot synthesis process using the heating of the ethylene glycol solution containing zinc nitrate hydrate, NH₃, and glucose achieved control of photoluminescence spectra and enabled the stable dispersion of ZnO nanoparticles.

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A novel hemostatic agent was prepared using phosphoryl oligosaccharides of calcium (POs-Ca), hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂; HAp] obtained by the hydrolysis of POs-Ca (i.e., sugar-containing HAp (s-HAp), Ca/P ratio = 1.56, 60.3 mass% calcium-deficient HAp and 39.5 mass% organic materials) and thermoplastic resin (random copolymer of ethylene oxide and propylene oxide; EPO). The gel formed by mixing the EPO with water (EPO/water mass ratio: 0.20) was flash frozen at −80°C and then freeze-dried at −50°C for 15 h. The freeze-dried material was blended with POs-Ca or s-HAp. The hemostat, whose consistency had been adjusted to that of commercial hemostat by adding water, possessed the stanching times: 6.0 h (s-HAp/EPO hemostat; s-HAp/EPO = 0.20) > 5.75 h (POs-Ca/EPO hemostat; POs-Ca/EPO = 0.20) > 4.75 h (EPO hemostat). The test for the implantation of these composite hemostats into the Japanese white rabbits indicated that the bone regeneration of s-HAp/EPO composite hemostat was excellent, compared to the case of POs-Ca/EPO composite hemostat. The loading of gentamicin, a typical antibiotic agent, to the s-HAp/EPO composite hemostat showed the steady state releasing in the phosphate buffered saline.

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Alkaline earth metal titanates ATiO₃ (A: Mg, Ca, Sr, Ba) were prepared from two types of layered potassium titanates [K₂Ti₂O₅ and K_0.6Ti_1.85O₄ (hereafter, Lss)] by using alkaline earth metal molten salts [ACl₂ + A(NO₃)₂ (1:1)]. For A = Ca a single phase of perovskite-type compound was prepared at 600°C by using both starting compounds and the reaction temperature was lower than in 400°C that of the solid state reaction with TiO₂ (anatase) and CaCO₃. A single phase of perovskite-type SrTiO₃ was obtained at 600 and 700°C for K₂Ti₂O₅ and Lss, respectively and these temperatures were much lower than that (1200°C) of the solid state reaction with TiO₂ (anatase) and SrCO₃. In the case of perovskite-type BaTiO₃ a single phase of perovskite-type compound was prepared at 700°C by using both starting compounds and also this temperature was much lower than that (above 1300°C) of the solid state reaction with TiO₂ (anatase) and BaCO₃. Although neither K₂Ti₂O₅ nor Lss could produce a single phase of ilmenite-type MgTiO₃, it was prepared by the solid state reaction with TiO₂ (anatase) and magnesium basic carbonate at 900°C. A single phase of ilmenite-type CdTiO₃ was prepared from K₂Ti₂O₅ by using cadmium molten salts [CdCl₂ + Cd(NO₃)₂ (1:1)] at 500°C. By taking account of the fact that ilmenite-type CdTiO₃ transforms to perovskite-type structure, this preparative method using layered potassium titanates with molten salts preferred to crystallize perovskite-type titanates at lower temperature rather than ilmenite-type ones.

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Barium titanate (BTO) hollow particles were prepared using two-step chemical solution deposition with a template particle. Polystyrene (PSt) was selected as the template particle, and N-(hydroxymethyl)acrylamide (HMAm) was polymerized as a comonomer to generate the hydrophilic group on the PSt template particle surface. The BTO monophase was attained at [Ba]/[TiO₂] = 1.0 using 350°C pre-annealed TiO₂ precursor hollow particles. The obtained BTO particle was a hollow structure with shell thickness of approximately 45 nm. The surface area of the obtained BTO hollow particle was 12 m²/g, which was approximately twice as large as that of alkoxide-derived BTO particles created with the same annealing temperature.

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Two kinds of heterometal coordination polymer precursors, {Sm[M(ox)₃]·nH₂O}_x (M = Fe and Co), were prepared by the reaction of K₃[M(ox)₃]·3H₂O with Sm(NO₃)₃·nH₂O in methanol solvent. These compounds were found to have oxalato-bridged network structure. On the other hand, the desired heterometal coordination polymer precursors could not be obtained by the present preparation method using water solvent. The thermal decomposition behaviors of these d-f heterometal coordination polymer precursors were investigated under air atmosphere. The perovskite-type oxides, SmMO₃ (M = Fe and Co), were found to form in the temperature range of >600°C. The specific surface area of SmFeO₃ powder increased with decreasing calcination temperature of Fe-containing heterometal coordination polymer precursor.

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Textured ceramic materials arouse recently great interest due to the effective improvement of their physical and mechanical properties compared to those not crystalline oriented. Feeble magnetic ceramics, such as alumina can be textured under high magnetic field of 12T during shaping process. The connection between shaping by gelcasting method and crystalline orientation of α-alumina in high magnetic field is reported in this paper. Gelcasting allows obtaining high-quality complex-shaped elements with small quantities of organic binders. A new environmentally friendly compound on the basis of glucose (3-O-acryloyl-D-glucose) was synthesized and applied as a monomer in gelcasting process. The ceramic slurries of solid loading 30–50 vol % have been exposed to high magnetic field at the time of consolidation through an in situ polymerization of used monomer. The degree of crystalline orientation of sintered at 1600°C bodies was evaluated by X-ray diffraction (XRD).

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The perovskite oxide, LaFeO₃, was synthesized by different preparation methods, i.e., the calcination of co-precipitated precursors [La(Ag)–Fe–CO₃ and La–Fe–CO₃] and a mixture of La₂O₃ and Fe₂O₃ (La–Fe–O). By using the solution of Ag, the formation temperature (600°C) of the LaFeO₃ single phase obtained by the calcining of La(Ag)–Fe–CO₃ was about 500°C lower than that of La–Fe–CO₃. The formation temperature of the LaFeO₃ single phase of La–Fe–O was 1100°C as well as that of La–Fe–CO₃. Their carbon oxidations were investigated by DSC (differential scanning calorimetry) measurements. The DSC exothermic peak of La_0.9Ag_0.1FeO_α obtained by the calcining of La(Ag)–Fe–CO₃ at 700°C occurred at 409°C and showed a higher carbon oxidation activity when compared to LaFeO₃ (477 and 562°C) obtained by the calcining of La–Fe–CO₃ and La–Fe–O at 1100°C. The carbon oxidation activation energies observed for the non-catalyzed and catalyzed reactions (mixture of La_0.9Ag_0.1FeO_α) were 160 and 130 kJ·mol⁻¹, respectively.

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A vanadium-oxide-based precursor fine powder was prepared by the reaction of vanadium metal and H₂O₂. A VO₂ powder with particles tens of nanometers in size was obtained by treatment of the precursor powder at 650°C in an H₂/Ar atmosphere. The particle size of the resulting VO₂ powder was 40 nm, and the transition temperature of the obtained VO₂ powder was 68.5°C.

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Solid-state reaction between carbonate and/or oxide precursors is a simple method to prepare ceramic powders. However, a high calcination temperature is required for this method because of limited diffusion during calcination. In this paper, we describe that the formation of β-CaSiO₃ by solid-state reaction is accelerated by water vapor. β-CaSiO₃ powders have been prepared by solid-state reaction between CaCO₃ and amorphous SiO₂ as a raw material. Single-phase β-CaSiO₃ was successfully prepared by one-step calcination at 800°C for 2 h in water vapor, while it seemed to be difficult to prepare the single-phase β-CaSiO₃ by calcination in air. Water vapor-assisted solid-state reaction is likely to be applicable to prepare other functional ceramic powders at low temperatures.

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Mo-doped tungsten-based photochromic composite films were fabricated using a peroxoisopolytungstic acid methanol solution, peroxoisopolymolybdenum acid methanol solution, and transparent urethane resin. The non-doped composite films showed photochromic properties by UV–Vis light irradiation. The reaction rate constant was 2.68 × 10⁻² min⁻¹. The increasing Mo/W ratio in the film caused a blue shift of the absorption peak of the film. The reaction rate constants k of films with Mo/W rates of 0.1, 0.5, and 1.0 were 3.00, 4.23, and 3.53 × 10⁻² min⁻¹. Those values were larger than that of a non-doped film. All composite films showed a reversible photochromic property, which was the coloring and bleaching property.

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Needle- and plate-like NaTaO₃ have been synthesized at low temperatures (<500°C) in three steps by a molten NaOH method. First, Na₃TaO₄ precursor was synthesized by the reaction of Ta₂O₅ with a molten NaOH at 450°C for 50 h in air. Then, Na₃TaO₃ precursor reacted with H₂O to form needle-like Na₇(H₃O)Ta₆O₁₉·14H₂O and plate-like Na₈Ta₆O₁₉·24H₂O intermediates in the process to wash the excess NaOH in the crucible with H₂O. The needle-like Na₇(H₃O)Ta₆O₁₉·14H₂O was the major product. Then, these intermediates transformed to NaTaO₃ through dehydrate intermediates by heating at above 500°C. The obtained NaTaO₃ had needle- and plate-like morphology with a perovskite structure.

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Luminescent nanoparticles based on zirconia (ZrO₂) and europium niobate (Eu₃NbO₇) were directly formed as a single phase of structure corresponding to cubic phase from the precursor solutions of NbCl₅, ZrOCl₂, and EuCl₃ under mild hydrothermal conditions at temperatures more than 180°C. The lattice parameter corresponding to cubic phase decreased with increase in the concentration of ZrO₂. The optical band gap of the nanoparticles with composition 50 and 90 mol % ZrO₂ in the ZrO₂ − 1/4(Eu₃NbO₇) system was 3.5 and 3.6 eV, respectively. The nanoparticles can be excited by ultraviolet light 395 nm (f–f transition) and emit orange (590 nm) and red light (610 nm) corresponding to Eu³⁺ from ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions, respectively. The photoluminescence intensity of the sample containing larger amount of ZrO₂ was superior to that of the sample, 50 mol % ZrO₂.

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NaNbO₃ (NN) nanoparticles were successfully synthesized by solvothermal method at 315°C. Some particles have column-like morphology and the others have sphere morphology. The average particle sizes of column-like and sphere particle are 13 and 47 nm, respectively. The NN particles synthesized by the solvothermal method were much smaller than those (average particle size was 590 nm) fabricated by the conventional solid-state method. High-dense (relative density: 95.4%) NN ceramics could be fabricated at low temperature (1150°C) in air using NN nanoparticles obtained by solvothermal synthesis. This sintering temperature is much lower than that (>1350°C) using NN particles obtained by the conventional solid-state reaction method. The fabricated NN ceramics from NN nanoparticles showed a piezoelectric property (d₃₃ = 17 pC/N).

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Sludge from the washing process of natural aggregate was used as the raw material for the production of dry pressed ceramic bodies. After fast firing at temperatures of 1000–1090°C with a 10-min soaking time, bodies based on waste sludge show considerably lower porosity (water absorption; bulk density), higher bending strength and better pore size distribution with respect to frost resistance than similar compared bodies based on spray granulate used for the production of dry pressed ceramic tiles.

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Purified squid ink was used as a natural dye in TiO₂ nanocomposite films for the fabrication of dye-sensitized solar cells (DSSCs). The squid ink extract was purified by the reaction over a proteolytic enzyme and coated onto composites of TiO₂ nanotubes/nanoparticles. The resulting cells were compared with reference DSSCs in which N719 was used as a standard dye. Analysis revealed that the sub-500-nm eumelanine-based spherical nanoparticles were well adsorbed on the surface of the TiO₂ nanotubes/nanoparticles, and the cells demonstrated efficiencies of 0.72 and 0.86%, respectively. The mechanisms over photosensitization induced by the purified ink particles are elucidated.

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