Artificial superlattice thin films of (Pb_0.9Sr_0.1)TiO₃ (PST)_n/SrTiO₃ (STO)_m were grown on SrRuO₃-electroded DyScO₃ (001)_pc substrates by pulsed laser deposition. X-ray diffraction (XRD) showed that the fabricated superlattice thin films have a good periodicity in the out-of-plane direction, indicating the sharp interfaces regardless of the difference in layer thickness. Synchrotron XRD indicated that the film with n/m = 14/20 had a weak periodicity in the in-plane direction, which may had arisen from the ordered polar vortex arrays existing in the PST layers. All the fabricated superlattice thin films showed the electric field-induced strain, though its magnitude was smaller than that for typical ferroelectric materials.

A SrZrO₃ thin film with yttrium (Y) concentration of 20 at % (SZYO) was successfully deposited by the pulsed laser deposition (PLD) technique. The laser power of PLD affected Y-concentration significantly even though it used the same PLD target. On contrary, the laser reputation frequency and the deposition temperature did not significantly affect the composition. The SZYO film deposited at the optimized conditions was well crystallized and showed no secondary phase and showed (111) and (110) orientations when they were deposited on (111)Pt/SiO_x/Si and on (111)Pd/(111)Pt/SiO_x/Si substrates, respectively. This SZYO film is expected to use as an electrode of our proposed novel solid oxide fuel cells.

Ba₃TaGa₃Si₂O₁₄ (BTGS) bulk single crystals were grown by the Czochralski method. The crystal structure of BTGS has been refined using single-crystal X-ray diffraction data with a precision corresponding to an R index of 0.018. The crystal structure is isostructural to La₃Ga₅SiO₁₄ which has the trigonal space group P321 and Z = 1, and the distribution of each cation is ordered in each site. Material constants and resistivity of the crystal were measured up to 550 °C. The results indicate that the BTGS crystal is a good candidate for piezoelectric applications in elevated temperatures.

Doping effects of Mn and Cu ions for (1 − x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ [BZT–xBCT] ceramics were investigated with the aim for high-power piezoelectric characteristics such as vibration velocity v_0–p, mechanical quality factor Q_m and piezoelectric constant d₃₁ at large amplitude vibration. The v_0–p is well known as proportional to a product of small signal d₃₁ and Q_m [d₃₁ × Q_m]. BZT–0.6BCT based ceramics were prepared by conventional solid-state reaction method. In the case of CuO doping, both d₃₁ and Q_m values were simultaneously improved by the doping amount of 0.1 wt % to BZT–0.6BCT ceramics, then the d₃₁ × Q_m value was 3 times larger than that of non-doped BZT–0.6BCT ceramics. On contrary to the case of co-doping of CuO and MnCO₃, MnCO₃ 0.6 wt % and CuO 0.1 wt % added BZT–0.6BCT ceramics showed significant improvement of Q_m, then the d₃₁ × Q_m value was approximately 6 times larger than that of non-doped BZT–BCT ceramics. The v_0–p of BZT–0.6BCT ceramics doped with MnCO₃ 1.0 wt % and CuO 0.1 wt % was increased significantly, which was larger than that of Pb(Zr,Ti)O₃-based ceramics. Temperature dependence of v_0–p was also investigated, and it was stable up to 80 °C. It was supposed availability of practical high-power piezoelectric applications at around room temperature.

Oxide electrolytes are a growing topic in battery research, but their full potential has not yet been realized owing to the lack of new materials. As opposite to the traditional design strategy that relies on d⁰ or d¹⁰ systems, we focus our attention on 3d⁶ systems, oxygen-excess La_2−yLi_xLi_0.5Co_0.5O_4.25 and oxygen-deficient La_4/3−xLi_3x+yLi_0.5Co_0.5O_4−δ. Among them, we achieve lithium-ion conduction in La_1.24Li_0.57Li_0.5Co_0.5O_3.15. A quasi-one dimensional pathway for lithium diffusion or distortion of lithium nuclear density is confirmed to be present at 100 °C by analyzing neutron powder diffraction data in combination with the maximum entropy method.

Polycrystalline ZnFe₂O₄ thin films were deposited on Si and porous Si (PSi) substrates using Dynamic Aurora pulsed laser deposition (PLD in a magnetic field). The average grain sizes of ZnFe₂O₄/Si and ZnFe₂O₄/PSi were, respectively, 120 and 48 nm. The ZnFe₂O₄/PSi thin film resistance was higher than that of ZnFe₂O₄/Si thin film. For ZnFe₂O₄/Si and ZnFe₂O₄/PSi thin films, the sensor response for liquefied petroleum gas was measured as a function of time and temperature. The sensor response of ZnFe₂O₄/PSi thin film measured at 375 °C is higher than that of ZnFe₂O₄/Si thin film. Results showed a steep initial rise in the temperature dependence of ZnFe₂O₄ thin films prepared using PLD. The dependence is steeper than that reported for ZnFe₂O₄ powder or thick and thin films prepared using chemical processing.

Ultrasonic sensors fabricated using (K,Na)NbO₃–KTiNbO₅ (KNN–NTK)-based lead-free piezoelectric ceramics were fabricated, their sensor characteristics were compared with those of sensors fabricated using Pb(Zr,Ti)O₃ (PZT)-based piezoelectric ceramics, and effects of material properties on sensor performance were investigated. The sound pressure, sensitivity, temperature increase during driving, and the responsiveness of the KNN–NTK-based sensor equaled those of the PZT-5A-based sensor. PZT-5A is generally used for ultrasonic sensors and has the same mechanical quality factor Q_m as the KNN–NTK ceramics. Most sensor characteristics are explained based on the electromechanical coupling factor and Q_m. However, the change in frequency characteristics under high applied power was observed that is attributed to the tendency of the nonlinear phenomenon of KNN–NTK-based ceramics to be weaker than that of PZT-based ceramics.

⟨111⟩-oriented BaTiO₃ (BT) ceramics were prepared by a high magnetic field assisted electrophoretic deposition method using hexagonal-tetragonal co-existing BT powders. With increasing the hexagonal content, the ⟨111⟩-orientation factor increased, while piezoelectric strain constant d^*₃₃ increased up to the hexagonal content of 80% with attaining a maximum value of 627 pm V⁻¹ and then rapidly decreased. In contrast, the decreasing trend of d^*₃₃ with increasing hexagonal content in the randomly oriented ceramics was observed. These results were discussed with the degree of the orientation and the possible twin defects in the BT ceramics.

A-site substituted (Ba_1−x,Sr_x)TiO₃ nanocubes (BS_xT NC; x is Sr ratio) were synthesized by hydrothermal process with surfactant and additives. X-ray diffraction profiles of BS_xT NCs showed single-phase of perovskite. Size of BS_xT NCs was decreased with increasing Sr content under same hydrothermal condition. When synthesis temperature increased, size of BS_xT NCs was enlarged. It revealed that the size of BS_xT NCs was able to be controlled by optimizing the hydrothermal conditions. However, inhomogeneous substitution was observed by scanning transmission electron microscopy with energy dispersive X-ray spectroscopy. It suggested that reaction rate of Sr ions to form perovskite structure was faster than that of Ba ions under hydrothermal condition. Three-dimensional (3D) assemblies of BS_xT NCs after heat-treatment at 850 °C had obscured interfaces between the NCs. Raman spectroscopy of NC assemblies revealed that symmetry of BS_xT NCs differed from that of BaTiO₃ (BT) NCs and did not change after heat-treatment at 850 °C. Piezoresponse curves became slim hysteresis behavior with increasing Sr ratio. These results suggested that Sr substitution of BT NCs caused phase transition from ferroelectric to paraelectric phase in 3D assemblies.

Single crystals of Li_xLa_(1−x)/3NbO₃ were grown in air using Czochralski method from La-poor melt. The lithium-ion conductivity of the crystals was measured. The length and maximum diameter of the boule grown were 23 and 20 mm, respectively. The boule contained no inclusions but was covered with a very thin polycrystalline film of LaNbO₄ and LiNbO₃ in its upper region. The composition of the crystals grown was estimated to be x = 0.15 and the starting melt composition was x = 0.20. The ionic conductivity of the crystal was anisotropic with σ_[100] = 2.8 × 10⁻⁴ S cm⁻¹ and σ_[001] = 9.7 × 10⁻⁵ S cm⁻¹ at 306 K. The activation energy, E_a of these conductivities was almost the same in the range of 0.28–0.29 eV. Further, we discussed the anisotropic lithium-ion conductivity of the crystal.

The possibility of bismuth (Bi) and nitrogen (N) co-doped barium titanate (BaTiO₃) as a ferroelectric material was investigated by calculation and experiment. From first principles calculations, it was found that Bi and N co-doped BaTiO₃ has a higher spontaneous polarization than undoped BaTiO₃ since dopant Bi and N ions contribute to the enhancement of covalent interactions between cations and anions. Because it was revealed that the ferroelectricity of BaTiO₃ can be improved by co-doping of Bi and N, we demonstrated the synthesis of (Ba,Bi)Ti(O,N)₃. Single phase oxynitride (Ba,Bi)Ti(O,N)₃ powder was fabricated by annealing (Ba,Bi)TiO₃ in NH₃ gas. The tetragonal distortion of (Ba,Bi)Ti(O,N)₃ was smaller than that of BaTiO₃, which may be due to A-site and O-site vacancies in the perovskite lattice introduced during NH₃ annealing.

The interface structure change between PbTiO₃ (PTO) thin films with various thickness grown on La-doped SrTiO₃(001) (La:STO) single crystal substrates by chemical solution deposition method was elucidated by (scanning) transmission electron microscopy ((S)TEM). The films were comprised of perovskite single phase and cube-on-cube orientation relationship with the substrate. STEM images revealed that the twin deformation precedes the nucleation of edge dislocations away from the coherent interface between the film and the substrate. Diffusion of Pb ions into the substrate was also observed through edge dislocations away from the interface. Edge dislocations climbs downward into the substrate with further diffusion of Pb ions increasing the film thickness. This phenomenon was not observed in the PTO film deposited on the non-doped STO substrate. Therefore, lattice defects in the La:STO substrate. the misfit dislocation induced by 90° domain formation as well as similar ionic radius between Pb and Sr ions appeared to facilitate the local interdiffusion of the constituent elements between the film and the substrate.

Using scanning transmission electron microscopy and electron energy loss spectroscopy, we have elucidated the local structure and the crystallization mechanism of amorphous phase PbZr_xTi_1−xO₃ (PZT) (x = 0.3) thin films deposited on SrTiO₃ (STO) (001) single-crystal substrates by chemical solution deposition. The amorphous phase involves the short-range order of (Ti/Zr)O₆ octahedra and Pb–O, and then, they are connected with the residual carbon. During the pyrolysis process, the first unit cells of the film has already crystallized with cube-on-cube epitaxial relationship with the STO substrate. The film–substrate interface is coherent and atomically sharp between the first Pb–O layer and the substrate. In the crystallization process, this layer seems to act as a seed layer for PZT epitaxial film growth. It accelerates crystal growth as a nucleation site and simultaneously shrinks the film by combustion of the residual carbon and subsequent densification, affecting the local coordination structure in the amorphous phase. The self-organized seed layer in the pyrolyzed film appears to play an important role in the epitaxial growth.

(K,Na)NbO₃ thick films were prepared at 240 °C on (100)_cSrRuO₃//(100)SrTiO₃ substrates by hydrothermal method. Film thickness increased using an amorphous niobium source instead of conventionally used crystalline one and have the maximum thickness at 0.5 mmol of input mass of niobium source within the range of 0.02–7.5 mmol in case of the 20 h deposition. The yield of (K,Na)NbO₃ films from 0.5 mmol amorphous niobium source becomes 20 times higher than that from conventionally used a 2 mmol crystalline niobium source. In addition, crystal structure, surface morphology, dielectric constant, and ferroelectric and piezoelectric properties of these films were almost independent of the kinds of niobium sources and their input mass within the limitation of the present results.

Piezoelectric LiNbO₃:Pr³⁺ has recently attracted attention as a so-called multi-piezo material, exhibiting simultaneously piezoluminescence and piezoelectricity. In order to investigate and improve the performance of piezoluminescence and piezoelectricity in the newly found multi-piezo material LiNbO₃:Pr³⁺, a systematic study has been carried out on both the crystal structural stability and the correlated multi-piezo performance through structure control between LiNbO₃ and NaNbO₃. Full set samples of Li_1−xNa_xNbO₃:Pr³⁺ (x = 0–1) with various Li/Na ratios were synthesized, and the crystal structure, piezoluminescence performance, piezoelectric property d₃₃, and their correlations were systematically investigated. We found that four crystal phases, LiNbO₃-R3c, NaNbO₃-R3c, NaNbO₃-P2₁ma, NaNbO₃-Pbma, can exist stably with co-existence in Li_1−xNa_xNbO₃:Pr³⁺ by controlling the Li/Na ratio. A strong correlation between piezoluminescence and piezoelectric properties was verified. Furthermore, the highest piezoluminescence intensity and piezoelectric constant were realized near the phase boundary of NaNbO₃-R3c and NaNbO₃-P2₁ma, demonstrating the crystal structure control as a promising technology to engineer multi-piezo materials.

CaS-based materials are known as highly efficient phosphors. CaS has excellent properties as host materials of phosphors under ultraviolet irradiation and is expected to have also for radiation detection. In this study, we fabricated CaS ceramic phosphors and measured their photoluminescence (PL), scintillation, and dosimetry characteristics to investigate the applicability of CaS ceramics as scintillators and dosimeters. The scintillation emission spectrum of CaS:Eu ceramics showed an emission peak at 656 nm, originating from the 5d–4f transitions od Eu²⁺ ions. The scintillation emission spectrum of CaS:Ce ceramics showed emission peaks at 510 and 570 nm that originate from the 5d–4f transitions of Ce³⁺ ions. The PL emission peaks of CaS:Ce and CaS:Eu were similar to those of the X-ray-induced radioluminescence emission peaks and were also assigned to the emission of Ce³⁺ and Eu²⁺ ions. The light yield of CaS:Ce and CaS:Eu were estimated to be approximately 1,700 and 4,400 photons/MeV, respectively. As for CaS:Eu, significant afterglow and strong thermoluminescence were observed, which indicates the sample contained trap sites at high concentration. Considering their PL, thermoluminescence, and scintillation properties, CaS:Ce and CaS:Eu have potentials for application as scintillators and dosimeters, respectively.

YVO₄:Eu³⁺ phosphor particles are proposed as an H₂O₂ sensing material based on their turn-off luminescence. The YVO₄:Eu³⁺ particles having various surface microstructures were synthesized through liquid processes and their H₂O₂ sensing ability was evaluated by immersing them in an aqueous H₂O₂ solution with a constant volume at a fixed concentration. The microstructures were characterized in detail not only by electron microscopy but also by nitrogen adsorption to elucidate factors governing the H₂O₂ sensing ability. It was then indicated that micro-/mesoporous structures, which were introduced in the micrometer-scaled spherical particles during their synthesis by a biphasic sol–gel method, were a decisive factor for achieving the effective H₂O₂ sensing. The YVO₄:Eu³⁺ particles synthesized under the improved condition could show a 37% decrease of luminescence intensity after the H₂O₂ treatment.

Y-doped HfO₂ films with various thicknesses were prepared on (100)-oriented [10 wt.% Sn-doped In₂O₃, ITO]//(100) [yttria-stabilized zirconia, YSZ], and (111)ITO//(111)YSZ substrates by a radio-frequency magnetron sputtering method. Almost a single phase of orthorhombic symmetry was obtained for all films. {100}-oriented epitaxial films were obtained on (100)ITO//(100)YSZ substrates, while the film orientation changed from {111} to {100} with increasing film thickness on (111)ITO//(111)YSZ substrates. {100}-oriented epitaxial Y-doped HfO₂ films were also obtained on (100)-oriented epitaxial ITO layers on (100)YSZ//(001)Si substrates. Ferroelectricity was observed for all films. Their remanent polarization (P_r) and coercive fields (E_c) were about 5 µC/cm² and 1 MV/cm, respectively, indicating that P_r and E_c were almost independent of the film thickness and kind of substrate.

Sodium manganese oxide for a cathode material of sodium-ion secondary battery was rapidly synthesized in 5–15 min by an improved microwave heating method with boron addition. Although prepared cathode materials included three types of Na_XMnO₂, it exhibited good electrochemical performance and delivered an initial discharge capacity of 200 mA h g⁻¹ at second discharge. Electrochemical activation of β-NaMnO₂ to α-NaMnO₂ during charge–discharge process was indicated by X-ray diffraction results.

Calcium phosphate-based bone regenerating materials were developed by utilizing interfacial interaction between inorganic–organic substances. Although apatitic calcium phosphates, hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP), have unique affinity to organic substances, and utilization of the affinity requires appropriate surrounding conditions. The author and his colleagues control the surrounding conditions to realize porous HAp ceramics with high porosity, interconnectivity and compressive strength, composite membrane of β-TCP and polylactide-based biodegradable polymers for guided bone regeneration, and bone-like nanocomposite of HAp and type-I atelocollagen (HAp/Col). Electrostatic interactions between calcium phosphates and polymers in these composites were presented by reflection infrared spectra. They also examined in vitro and in vivo and demonstrate good bone regeneration properties. Particularly, the HAp/Col exhibits completely incorporation into bone remodeling process that is the first in the world for synthetic materials. Three of these materials are also commercialized and used in medical and dental fields and contribute to human health.

β-tricalcium phosphate (β-TCP) with interconnected pores is an attractive substitute for bone because it shows excellent tissue response and osteoconductivity. An interconnected porous structure is a key factor for fast osteoconductivity, because it facilitates tissue and cell penetration. However, it is challenging to attach interconnected porous structure to β-TCP blocks. In this study, a new, simple, and safe method for fabricating interconnected porous β-TCP was developed, based on an analogous dental glass ionomer cement setting reaction. β-TCP granules were mixed with polyacrylic acid (PAA) by loading; PAA got bound to these granules and got set to form an interconnected porous structure; the sintering process decomposed PAA and yielded the interconnected porous β-TCP structure. Diametral tensile strength and porosity of the fabricated samples were 1.3 ± 0.2 MPa and 57.6 ± 1.1%, respectively. These values of samples were enough value for applying bone substitute. β-TCP with interconnected pores synthesized using the novel method described, herein, would be a suitable bone substitute in clinical settings.

The Fukushima nuclear power plant accident caused an outflow of pollutants. Thus, precautionary measures must be taken by using preventive materials for the deterrence of such accidents. Herein, we aimed to develop inexpensive materials that can remove radioactive elements from an aqueous solution. We found that powders obtained from milling scallop shells, which were discarded in large quantities, removed Sr²⁺ from aqueous solutions. The Sr²⁺ removability of the scallop shell powder improved with milling time, indicating the influence of increase in the specific surface area on Sr²⁺ removability. Despite of the same specific surface area, the scallop shell powder exhibited higher Sr²⁺ removability than that of the unmilled CaCO₃. Differential scanning calorimetry evaluation for the investigation of factors other than the specific surface area revealed that the milled scallop shell powder contained amorphous calcium carbonate. Moreover, we synthesized amorphous calcium carbonate and found that it exhibited 60-times higher Sr²⁺ removability than that of crystalline calcium carbonate. We concluded that the amorphous structure of calcium carbonate significantly affects the Sr²⁺ removability from aqueous solutions. It was hypothesized that amorphous calcium carbonate removes Sr²⁺ by incorporating Sr²⁺ into the structure during crystallization in an aqueous solution.

The La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) ceramics co-doped with Ca²⁺ and different transition metal cations (Fe³⁺, Cr³⁺) were fabricated by the pressureless-sintering method. The influence of doping on the phase structure, microstructure and infrared emissivity (0.75–2.5, 3–5, 8–14 µm) was investigated. The infrared emissivity of LZ7C3 in the wavelength range 0.75–2.5 and 3–5 µm was significantly enhanced by co-doping, especially with Ca²⁺ and Cr³⁺. The infrared emissivity in the wavelength range 0.75–2.5 µm could be improved from 0.069 (LZ7C3) to 0.876 at room temperature, and from 0.463 (LZ7C3) to 0.877 in 3–5 µm at 300 °C, by co-doping with Ca²⁺ and Cr³⁺. On the other hand, doping had an insignificant effect on the infrared emissivity of LZ7C3 in the 8–14 µm range at 300 °C due to its high emissivity value (0.962) in the 8–14 µm range.

Our study shows that machine learning technique, Bayesian optimization (BO) can efficiently find high-refractive-index glasses from a large number of candidate compositions using data from the INTERGLAD database. The effect of the parameters (i.e., descriptors) input to the BO algorithm on search performance is described. The results show that elemental-property-based (EPB) descriptors, recently applied in materials science, are more effective than the component-amount-based ones traditionally used in the study of glass. The results suggest that BO with EPB descriptors can accelerate the search for glass compositions with desirable properties.

Inorganic–organic nanocomposite gas barrier membranes with high content of layered double hydroxide (LDH) using surface modified LDH on plastic film were prepared by cross-linking reaction. The effect of LDH content on the gas barrier properties [oxygen permeation and water vapor transmission rate (WVTR)] of the membrane was investigated. The oxygen permeability coefficient of the nanocomposite layer was small, and about one-tenth of polyvinylidene chloride (PVDC) and WVTR (thickness 25 µm) of the nanocomposite layer was on the same order as PVDC. The pencil hardness (750 g load) of the nanocomposite membrane was higher than that of substrate, polyethylene terephthalate film. The value was HB. The balance between high gas barrier properties and hardness were thought to be due to the well-dispersed inorganic component (LDH) and organic component in the nanocomposite. From the results, it was found that the reported inorganic–organic nanocomposite membranes can be applied to gas barrier membranes.