We prepared oxygen-deficient strontium titanate ceramics and measured the THz dielectric spectra to discuss the effect of oxygen vacancies on the intrinsic dielectric permittivity. In the presence of oxygen vacancies, the lattice volume of strontium titanate increased. First-principles calculation revealed that the expansion of the lattice originated from repulsion between the oxygen vacancies and cations, causing a decrease in the covalency of the Ti–O bonding. THz dielectric measurement using a far-infrared spectroscopic ellipsometer made it clear that the Slater-type phonon mode hardened and then the intrinsic permittivity of strontium titanate decreased in the presence of oxygen vacancies.

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Ferrolectric orthorhombic HfO₂-based films are potential candidates for future ferroelectirc applications. The stability of the orthorhombic phase of epitaxial YO_1.5-substituted HfO₂ films on (111) yttria-stabilized zirconia substrates was investigated for various compositions, thicknesses and underlying layers. In the case of 14 nm-thick films, only 7 mol % film consisted of a single orthrohombic phase. With decreasing amount of YO_1.5 or increasing thickness, the paraelectric monoclinic phase formed in the films. On the contrary, the highly symmetric phase was grown by the increasing amount of YO_1.5. The effect of the underlying layer was also investigated. Differences in the degree of relaxation of the buffer layer give different amounts of the monoclinic phase. These results imply the importance of the compostions as well as of the strain state to (111)-oriented epitaxial Y-substituted HfO₂ films.

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Self-assembled Pb(Zr,Ti)O₃ (PZT) nanorods were grown by pulsed laser deposition (PLD) at an elevated oxygen pressure. PZT grew as a film in the initial growth stage and formed nanorods upon further deposition. The influence of the substrate temperature, target-substrate distance, and Pb composition of the targets on nanorod growth was investigated. It was found that the average radius of the PZT nanorods was larger at higher substrate temperatures and longer target-substrate distances, which can be explained respectively by the enhanced surface diffusion and shadowing effect of the PLD species. The results of this study can contribute to controlling the sizes of PZT nanorods to tune their piezoelectric response.

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{001}_c-oriented (K_0.86Na_0.14)NbO₃ thick films were prepared at 240°C on (100)_cSrRuO₃//(100)SrTiO₃ substrates by repeated hydrothermal deposition technique. The film thickness was found to increase linearly with the number of deposition cycles, and 60 µm-thick film was obtained after nine repetitions of the deposition. The K/(K+Na) ratio of the deposited thick films, measured by X-ray fluorescence spectroscopy, showed constant values regardless of the number of deposition cycles. Cross-sectional scanning electron microscopy images revealed uniformity of the obtained dense films with no obvious micro cracks and pores. Structural characterization based on X-ray diffraction, XRD 2θ-ω patterns and X-ray pole figure measurement, showed that the epitaxial relationship between the films and substrates with a {001}_c orientation was maintained throughout the deposition cycles. In addition, cross-sectional Raman spectra showed that 60 µm-thick (K_0.86Na_0.14)NbO₃ film had an orthorhombic structure. The dielectric constant, ε_r, and tan δ showed frequency dependence. The average remanent polarization measured at 100 Hz was 8 µC/cm².

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A facile synthesis method of delafossite-type CuYO₂ using a layered yttrium hydroxide (LYH) was developed. LYH microplates and Cu₂O nanoparticles were both prepared from aqueous solutions and used as raw materials for the solid-state reaction to form CuYO₂. It was found that CuYO₂ could be obtained by heating LYH–Cu₂O mixed powder at 900°C for 4 h under a N₂ atmosphere. Although the product contained a slight amount of Y₂O₃, the heating time used in the proposed method was much shorter than that required for the conventional synthesis method via the Cu₂Y₂O₅ precursor phase. Analysis of the X-ray diffraction pattern showed that the CuYO₂ powder synthesized using LYH contained the 3R-type polymorph as the major content, whereas a larger content of the 2H-type polymorph was included in the powder synthesized by the conventional method. Based on these results, a topotactic reaction maintaining the layered structure of LYH was proposed as the formation mechanism for CuYO₂ in LYH–Cu₂O mixed powder.

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Metal oxides containing the divalent zinc cation (Zn²⁺, d¹⁰ electronic configuration) as an essential element are promising candidates for oxide-ion conductors, because there are several good oxide-ion conductors containing other d¹⁰ cations, such as Ga³⁺ and Ge⁴⁺. In the present study, we have found a new structure family of oxide-ion conductors, BaY₂CuO₅-type (BaCuY₂O₅-type) BaR₂ZnO₅ compounds (R = rare earths). BaR₂ZnO₅ compounds with a BaY₂CuO₅-type structure were found to be good candidates for oxide-ion conductors by the bond-valence method. BaR₂ZnO₅ compounds (R = Sm, Gd, Dy, Er, and Ho) were synthesized by solid-state reactions, and their electrical conductivities and crystal structures were investigated. Rietveld analyses of BaR₂ZnO₅ (R = Sm, Gd, Dy, Er, and Ho) using synchrotron X-ray powder diffraction data gave good fitting for the BaY₂CuO₅-type structure. BaHo₂ZnO₅ had the highest total electrical conductivity in air among BaR₂ZnO₅ compounds (R = Sm, Gd, Dy, Er, Ho). Oxide-ion conduction was confirmed for BaHo₂ZnO₅ by electrical conductivity measurements conducted under various oxygen partial pressures. Neutron powder diffraction data of BaHo₂ZnO₅ were analyzed by the Rietveld method, and the oxide-ion conduction paths were investigated by the bond-valence method.

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We report the effects of Sr or Ba substitution on the crystal growth and electrical and mechanical properties of Ca₂Al₂SiO₇ (CAS) piezoelectric single crystals, which are suitable for use in high-temperature pressure sensors. Ba was scarcely incorporated in the crystal lattice of CAS. Strontium-substituted CAS single crystal with a nominal chemical composition Ca_0.75Sr_1.25Al₂SiO₇ (CSAS125) was grown by the Czochralski method. Although the piezoelectric modulus d′₃₁ of CSAS125 is a bit lower than that of the CAS crystal, the rupture strength of the (XYt)45° rotation cut substrate of CSAS125 crystal was 170 MPa, which was 1.2 times higher than that of CAS crystal. By considering the rupture strength and the apparent piezoelectric d^*₃₁ coefficient calculated for the crystal rotation cut of CAS crystal, the CSAS125 crystal substrate with a rotation cut of (XYt)25° was found to indicate a rupture strength of 220 MPa and a piezoelectric d′₃₁ coefficient of approximately 2 pC/N.

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To meet recent requirements for high-performance dielectric capacitors, we have attempted to develop new boundary layer (BL) ceramic capacitors consisting of conductor grains epitaxially covered with insulator boundary layers to improve their dielectric breakdown strength. First, we attempted to synthesize conductor-insulator core–shell particles with epitaxial interfaces, because the desired BL capacitors can be prepared by assembling these core–shell particles. One of the conductive perovskite oxides, lanthanum nickel oxide (LaNiO₃, LN), was selected as the conductor layer, and bismuth potassium titanate [(Bi_1/2K_1/2)TiO₃, BKT], which has a similar lattice constant to LN, was selected as the insulator layer. LN nanoparticles synthesized by the sol–gel method were mixed with the titanium oxide (TiO₂) and bismuth nitrate [Bi(NO₃)₃] in the KOH aqueous solution, and hydrothermal treatment was performed at 160°C. LN–BKT powders could be obtained in the presence of the Bi and Ti sources without decomposition of LN. This fact suggests that the BKT coating layers formed initially on the surface of the LN nanoparticles and prevented a decomposition reaction of LN in the KOH aqueous solutions. The formation of a core–shell structure in the LN–BKT powders was confirmed by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy observation revealed epitaxial growth of a BKT shell layer on the LN core nanoparticles.

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Dense Mn-added 0.3BaTiO₃–0.1Bi(Mg_1/2Ti_1/2)O₃–0.6BiFeO₃ (0.3BT–0.1BMT–0.6BF) ceramics were fabricated by spark plasma sintering of 0.3BT–0.1BMT–0.6BF powders with different powder sizes of 0.3, 1.0, and 1.4 µm. It was found that use of larger powders suppressed Bi volatilization during the sintering, which was judged by maintained perovskite A site/B site component (A/B) ratios of 1.000 and 0.997 for the 1.0 and 1.4 µm samples and a decreased A/B ratio from 1.000 to 0.998 for the 0.3 µm sample. Grain sizes of the ceramics prepared from the 0.3, 1.0, and 1.4 µm powders were 0.7, 1.2, and 1.9 µm, respectively. These results contributed to increased remanent polarizations of 6.7, 28.3, and 36.6 µC/cm² and maximum electric-field-induced strains/applied electric fields (S_max/E_max) of 251, 332, and 362 pm/V for the 0.3, 1.0, and 1.4 µm samples, respectively. Comparison with conventionally sintered ceramics was also made.

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The electric field-dependent crystal structures and electrical properties were investigated in the 0.67BiFeO₃–0.33BaTiO₃ (BF33BT) lead-free piezoelectric ceramics. The room temperature synchrotron radiation X-ray diffraction (SR-XRD) patterns measured, without the application of an electric field, revealed all the peaks to be single suggesting the cubic like crystal structure of the BF33BT system. The domain switching was ascertained in the P–E hysteresis loop and S–E curve meanwhile, SR-XRD patterns exhibited beyond doubt single peak. In order to study the electric field induced structural phase transition, SR-XRD was measured in BF33BT ceramics as a function of electric field. The electric field applied up to 40 kV/cm with bipolar cycling was parallel along the longitudinal lattice response direction that was similar for the piezoelectric response measuring method. The shift of SR-XRD peaks to lower and/or higher angle in comparison to the peak position of zero field-SR-XRD was found to depend on the direction and intensity of the applied electric field. The peak shape under maximum electric field was quite same that of SR-XRD patterns at zero electric field. Importantly, the single peak shape was maintained for all the SR-XRD measured under the electric field. Therefore, the electric field induced structural phase transition did not occur in the BF33BT ceramics.

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Single-crystalline barium zirconate titanate nanocubes (BZ_xT NCs; x is Zr contents) with various composition of Zr/Ti ratio were synthesized by hydrothermal method using water-soluble titanium and zirconium complex and surfactants. The highly-ordered assemblies of the BZT NCs were directly fabricated on the substrate by dip-coating method with low withdrawal rate. High dielectric constant above 4200 and relative low loss tangent below 1% with extremely small frequency dependence were achieved in the case of BZ_0.2T NC assembly. The temperature dependence of capacitance of BZ_0.1T NC assembly was quite small from −60 to 150°C. A specific peak in the Raman spectra of BZ_0.2T NC assembly was slightly shifted to lower wavenumbers from 294 to 288 cm⁻¹ after heat-treatment which meant the change of local bonding condition was induced by local strains at the interfaces. Zr-substitution and local strain synergistically affected to the dielectric properties of BZT NC assemblies.

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Cubical Pb(Zr,Ti)O₃ (PZT) crystals (PZT cubes) were synthesized using a hydrothermal method at different synthesis temperatures from 140 to 220°C. The Pb(Zr_0.52Ti_0.48)O₃ precursor solution was prepared from Pb(CH₃COO)₂·3H₂O, Zr(OH)[(OCH(CH₃)COO⁻]₃(NH₄⁺)₃, and titanium (IV) bis(ammonium lactato)dihydroxide. In this study, the effects of synthesis temperature on the shape, morphology, and crystallinity of PZT crystals were investigated. We successfully obtained PZT cubes possessing faceted structures without circular shaped PX-phase (Ti-rich PZT) at a synthesis temperature of 180°C; these PZT cubes consisted of perovskite phase without any non-ferroelectric pyrochlore phase. Precise analysis based on selected area electron diffraction and energy-dispersive X-ray spectroscopy revealed that PZT cube was a single crystal and the chemical composition of PZT cubes was closed to the nominal composition of the PZT precursor solution, respectively. PZT cubes with single perovskite phase could be synthesized at a lower temperature of 180°C by the hydrothermal method, compared with conventional methods such as sol–gel process and metal organic decomposition method. The piezoelectric properties were confirmed for single PZT cubes using the piezoresponse force microscopy mode of a scanning probe microscope.

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Concentrating ⁶Li isotopes, which exist only approximately 7.6% in nature, to 40 to 90%, is necessary for development of thermal fusion reactors, which are promising as next-generation base-load energy systems. We investigated the possibility of ⁶Li enrichment by electrochemical pumping using La_0.57Li_0.29TiO₃ solid lithium electrolytes. We also clarified the influence of potential application profiles on separation efficiency. Giving a potential difference to electrodes prepared on both sides of the electrolyte made the electrode on the lithium solution side positive and concentrated ⁶Li. The efficiency of lithium isotope enrichment was affected by the potential application profile. An intermittent potential application concentrates ⁶Li with high efficiency. In an intermittent potential application in which the electrode on the lithium solution side was positive, an ⁶Li concentration with higher efficiency was achieved when a small negative potential was applied to the lithium solution side electrode while suspending application of the positive potential.

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Polytetrafluoroethylene (PTFE), composed of fluorine and carbon atoms, has a potential to produce carbon-coated fluorides in the calcination of inorganic compounds. We synthesized high voltage cathode material for Na ion secondary battery, Na₂FePO₄F, using PTFE as the carbon-coating and fluorine source. The Na₂FePO₄F carbon-coated by a thermal decomposition of PTFE showed high discharge capacity (64.4 mAh g⁻¹) at the first cycle of galvanostatic cycling by the improvement of conductivity.

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Crystal structure and neutron scattering length density distribution of a pyrochlore-type ytterbium titanate Yb₂Ti₂O₇ have been investigated by in situ neutron powder diffraction measurements at 293 and 1173 K, Rietveld analysis and maximum-entropy method (MEM). In the MEM neutron scattering length density distributions of Yb₂Ti₂O₇, the oxide ion O_48f bonding to Ti cation was relatively localized at lower temperature of 293 K, while it was largely distributed at a higher temperature of 1173 K. At 1173 K, one oxide-ion diffusion path along the ⟨110⟩ unshared edge of TiO₆ octahedron was clearly visualized and the other oxide-ion diffusion path along ⟨100⟩, strictly ⟨2 −8x(O_48f) + 3 8x(O_48f) − 3⟩, shared edge of TiO₆ octahedron was also indicated. Here x(O_48f) is the atomic coordinate x of O_48f anion. The MEM neutron scattering length density distribution and difference bond valence sum map at 1173 K strongly suggested that the energy barrier for oxide-ion migration along ⟨110⟩ directions was lower than that along the ⟨100⟩ one. Oxide ions three-dimensionally diffuse through both the ⟨110⟩ and ⟨100⟩ paths across the unit cell.

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In this paper, the out-of-phase (OP) thermomechanical fatigue (TMF) hysteresis of fiber-reinforced ceramic-matrix composites subjected to different loading sequences has been investigated. The relationships between the OP TMF hysteresis, fiber/matrix interface debonding/sliding and multiple loading sequence have been established. The OP TMF hysteresis loops and interface damage for different loading sequences, cycle numbers and thermal cyclic temperature ranges have been analyzed. Comparisons of OP TMF hysteresis between single and multiple loading sequences have been conducted. The stress–strain hysteresis loops and fiber/matrix interface debonding/sliding of cross-ply SiC/MAS composites subjected to single and multiple loading sequences have been predicted.

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Au–SrTiO₃ nanocomposites were prepared using a photocatalytic reduction method by which the Au nanoparticles with particle size of 7–26 nm were deposited on the surface of SrTiO₃ particles with an average diameter of ∼55 nm. The structure, morphology and optical properties of products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Transmission electron microscopy and UV–visible diffuse reflectance spectroscopy. It is found that the loaded Au nanoparticles on SrTiO₃ particles exist in the metallic state, and the surface plasmon resonance absorption band centered around 557 nm is obviously detected in the diffuse reflectance spectra of Au–SrTiO₃ nanocomposites. The photocatalytic activities of samples toward the degradation of dyes (acid orange 7 and methyl orange) were evaluated under simulated sunlight and visible light irradiation. The results indicate that the decoration of Au nanoparticles can effectively improve the photocatalytic activity of SrTiO₃, and the catalytic efficiency of composites is related to the content of Au. More importantly, the Au–SrTiO₃ nanocomposites exhibit much higher photocatalytic activity under simulated sunlight than under visible light. In addition, a possible promotion mechanism of Au nanoparticles on the photocatalytic activity of SrTiO₃ was proposed.

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This study investigates the influence of GeO₂ on the nonlinear coefficient (α) and breakdown voltage (E_B) of TiO₂–Ta₂O₅–CaCO₃ varistor ceramics doped with GeO₂ and prepared according to a conventional ball milling–molding–sintering process. The electrical performance parameters, including the nonlinear coefficient (α), breakdown electric field (E_B), and leakage current (J_L), were assessed using a varistor direct-current instrument. The average barrier height Φ_B of each sample was calculated using the relevant formula. Analyses conducted by X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy demonstrated that GeO₂ doping changed the microstructures of TiO₂–Ta₂O₅–CaCO₃ ceramics, resulting increased α and decreased E_B values. Ceramics doped with 0.2 mol % Ta₂O₅, 0.2 mol % CaCO₃ and 0.9 mol % GeO₂ exhibited the maximum α value (α = 9.8) and the highest grain boundary barrier (Φ_B = 0.92 eV) but a low E_B value (E_B = 17.2 V·mm⁻¹).

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The room temperature growth of ZnO nanoneedle arrays on seed layers was demonstrated via wet-chemical synthesis. The orientation of ZnO nanoneedles was found to be extremely high on the flat seed layer with high crystallinity, whereas a poor orientation was observed on rough seed layers. We expect that the direction of ZnO [0001] (c-axis) dictates the orientation of ZnO nanoneedles. With longer reaction time, ZnO nanoneedles grew dominantly in a length compared to a diameter. Dense ZnO nanoneedles with a high orientation is believed to be promising for many applications in optelectronics and photonics.

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Calcium doped bismuth ferrite (BiFeO₃, BFO)-barium titanate (BaTiO₃, BTO) powders were successfully synthesized by a facile sol–gel route. Subsequently as-synthesized powders were packed within a fugitive silver metal tube and formed into tapes with uniform thickness by means of cold drawing and rolling processes, which is called powder in tube (PIT) method. The influence of calcining temperature on the crystalline structure and characterization of BFO-based tape was also studied. The particle size of tape prepared by PIT method is becoming smaller, indicating PIT method has great effect on refined particle. Furthermore, the remanent magnetization 2Mr and coercive force Hc for the tape are 0.092 emu/g and 281.59Oe, respectively. The optimized calcining temperature for the tape is 400°C.

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Hexagonal GdF₃:Tm³⁺, which is thermodynamically unstable at room temperature, was successfully crystallized in borosilicate glass using a phase separation technique. The crystal structure of GdF₃ was controlled by the addition of alkaline earth metals to the glass composition. Increasing the amount of SrF₂ added to the glass composition to 1.65 mol % increased the amount of precipitation of hexagonal GdF₃:Tm³⁺ crystals and the luminescence intensity. Lanthanide trifluoride phosphors were restrictively obtained in the borate phase as a result, and the emission of Tm³⁺ at 458 nm was observed. Furthermore, the luminescence intensity of GdF₃:Tm³⁺ in the phase separation glass upon SrF₂-doping was about three times larger than that without doping.

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Nano-sized ZnGa₂O₄, ZnGa₂O₄:Cr and ZnGa₂O₄:Ti phosphors were synthesized by low-temperature combustion method and the luminescent properties were studied in comparison with those from conventional solid-state reaction. The combustion reaction resulted in a single-phase spinel structure and the particles were 5–10 nm in size. Of all samples, undoped nano ZnGa₂O₄ exhibited an intrinsic blue emission and Ti-doped nano ZnGa₂O₄ had a tendency of white emission whereas Cr-doped nano ZnGa₂O₄ showed red emissions. Titanium ions in spinel structure was found to exist as in Ti³⁺ and Ti⁴⁺, but favouring trivalent state. The oxidation state of Cr ions was confirmed as 3⁺ in nano ZnGa₂O₄.

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Low heat Portland cement (LHC) containing expansive additives can reduce the temperature stress and the crack generation of concrete, therefore it can be used for producing mass concrete and high-strength concrete. However, since LHC does not contain much aluminum, it is difficult for LHC to immobilize chloride ions and be used in salt damage environments such as seashore. CaO·2Al₂O₃ addition to LHC can be the countermeasure, however chloride immobilization in LHC with CaO·2Al₂O₃ has not been researched in detail. This paper describes the influence of CaCl₂ addition on hydration of LHC containing an expansive additive and CaO·2Al₂O₃. In LHC containing an expansive additive, ettringite was mainly generated with and without CaCl₂. In contrast, in LHC containing an expansive additive and CaO·2Al₂O₃, monosulfate was generated without CaCl₂, and Friedel’s salt were generated with CaCl₂. Therefore, LHC containing an expansive additive and CaO·2Al₂O₃ showed potential for chloride ion immobilization.

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Pt–Rh/CeO₂/Al₂O₃ was successfully synthesized by the hydrothermal method, and its chemical and physical properties as well as its catalytic activity were evaluated. Pt–Rh/CeO₂/Al₂O₃ was also synthesized by the conventional impregnation method for purpose of comparison. Pt–Rh/CeO₂/Al₂O₃ synthesized by the hydrothermal method comprised hollow CeO₂ nanorods coated with nanoparticle arrays that served as selective supports for Pt and Rh on CeO₂ surfaces. Although the lights-off temperatures of NO and C₃H₆ were similar for Pt–Rh/CeO₂/Al₂O₃ catalysts synthesized by the two methods, moreover, Pt–Rh/CeO₂/Al₂O₃ synthesized by the hydrothermal method exhibited a lower lights-off CO temperature than that synthesized by the impregnation method. Pt–Rh/CeO₂/Al₂O₃ synthesized by the hydrothermal method also exhibited better catalytic activity, which was attributed to its better dispersion of Pt and Rh than that synthesized by the impregnation method.

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La-added and pure MgFe₂O₄ powders were prepared from a malic acid complex, and the effect of La-adding on the microstructure and specific surface area of MgFe₂O₄ powder were examined. There were no traces of impurity phases for pure MgFe₂O₄ powder in the X-ray diffraction measurement after calcination in the range of 600 to 800°C. When La atoms were added to MgFe₂O₄, the crystallite growth of MgFe₂O₄ was suppressed remarkably, resulting in a higher specific surface area in comparison with the pure material, and the lattice volume increased. X-ray photoelectron spectroscopy measurements showed that the binding energies of Mg 2s, Fe 2p, O 1s, and La 3d signals were in good agreement with the Mg²⁺, Fe³⁺, O²⁻, and La³⁺ valence states, respectively. Scanning electron microscopy observations revealed that MgFe₂O₄ powder shows an aggregation of granular particles and that the individual particles are tightly interconnected with each other, whereas smaller particles compared with pure MgFe₂O₄ were observed for the La-added powder. It was found from the N₂ adsorption measurement, moreover, that the amount of mesopore increases with La addition.

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Glass mixtures based on turquoise blue glaze were synthesized by the conventional ceramic method, and their color properties were investigated as environmentally friendly Co-free inorganic blue pigments. Samples showed coloring from light blue to black depending on their compositions. The bluest color was observed for 0.60 BaO·0.20 Li₂O·0.20 Na₂O·0.45 Al₂O₃·2.50 SiO₂ in a 20 wt % CuO sample heated at 900°C, which had the following color parameters: (L*a*b*) of L* = 41.9, a* = −4.5, and b* = −14.2. The a*, b* values are comparable to those of commercial Co-based blue pigments. Since the glass mixtures do not include cobalt oxide as a raw material, it should be an attractive alternative to conventional Co-based inorganic blue pigments.

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