Single-phase powders of LaMnO₃ and LaCoO₃, lanthanum-based perovskites, were synthesized using the citric acid combustion method. The surface concentration of La in the obtained powder was higher in LaCoO₃ than in LaMnO₃. These samples decomposed 2-naphthol in water in the dark. The decomposition reaction is attributed to the Mars–van Krevelen (MvK) mechanism because of the temperature dependence, activation energy, valence change during the reaction, and the amount of ion elution into water. A disproportionation reaction was confirmed for Mn in LaMnO₃. Both samples exhibited antibacterial and antiviral activity against Escherichia coli, Staphylococcus aureus, bacteriophage Qβ, and bacteriophage Φ6. The antibacterial activity was higher than the antiviral activity. LaCoO₃ tended to have higher antibacterial and antiviral activity than LaMnO₃ had. Results show that these materials had less ion leakage than that reported earlier for La₂Mo₂O₉.

In this study, we investigate the phase transitions of a promising perovskite niobate, RbNbO₃, by synchrotron X-ray diffraction, differential scanning calorimetry, and dielectric property measurements. This compound shows a first-order orthorhombic–tetragonal phase transition at 519 K and does not undergo a transition to a rhombohedral phase down to 5 K. Notably, the spontaneous polarization of the orthorhombic phase is larger than that of a well-studied isostructural perovskite niobate, KNbO₃.

Room-temperature (RT) epitaxial growth of ZnO thin films on flexible cyclo-olefin polymer (COP) substrates coated with the exfoliated β-Ga₂O₃(100) single crystal thin sheets as a seed layer was investigated using the pulsed laser deposition technique. Scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) measurements demonstrated that c-axis-oriented epitaxial ZnO(0001) thin films were obtained at RT on the exfoliated β-Ga₂O₃(100) seed layer bonded to the COP substrate. Also, the epitaxial relationship between the ZnO thin films and β-Ga₂O₃(100) seed layer was ZnO(0001)/β-Ga₂O₃(100) with ZnO[1120] ∥ β-Ga₂O₃[010] and ZnO[1100] ∥ β-Ga₂O₃[001]. The optical transmittance of the thin film, including the seed layer was more than 80 % in the visible light region. The optical band gap and the electrical resistivity of the ZnO thin film were estimated to be about 3.4 eV and about 2.1 × 10⁻³ Ω cm at RT, respectively.

SrO-terminated terraces were formed along TiO₂-terminated step edges by annealing (001) surfaces of SrTiO₃ single crystal originally with step-terrace structure fully terminated at TiO₂ atomic layer. The prepared step-terrace structure with the two different terminations were visualized in a wide field of view using scanning electron microscopy (SEM) under a low acceleration voltage of 1 kV and a short working distance of 2 mm. The different termination was clearly identified by an in-column secondary electron detector even in the wide-field region with dimensions of 30 × 30 µm². As results, the uniformity of the step-terrace structure was found to be limited only at a localized area. The wide-field observation revealed that there exist many “step-defects” such as pinning of the step lines and wandering so large that it goes around to an opposite side. Step-defects were present in at least several for 30 × 30 µm² sized observation areas with a probability of about 60 %.

Nd³⁺-doped Y₃Al₂Ga₃O₁₂ garnet ceramic pellet was prepared by solid state reaction and used as prototype to investigate the potential of Nd³⁺-activated garnet phosphors as Boltzmann thermometers for cryogenic and high temperature ranges. Despite the conventional use of the near-infrared emitting Nd³⁺-activated phosphors for biological applications, their real use is hindered by a low sensitivity in the physiological temperature range. Instead, the photoluminescence analysis in the 100–800 K range demonstrated interesting performances in both the cryogenic and high temperature ranges. Indeed, by taking advantage of the Stark levels of ⁴F_3/2 (Z-levels) and the ratio between the emission from the ⁴F_5/2 and the ⁴F_3/2 excited states is possible to build two reliable Boltzmann thermometers in the same material working in the cryogenic temperature range (100–220 K) and at high temperatures (300–800 K), respectively.

Ti₂AlC MAX phase ceramics are excellent candidates for high-temperature heat resistant materials. In addition, they are machinable using cemented carbide tools. However, heavy machining induces many surface cracks, reducing the mechanical strength and reliability of ceramic parts. Herein, we investigated the influence of the machining process on the bending strength and microstructure of Ti₂AlC ceramics. Nearly fully dense Ti₂AlC ceramics with elongated grains were machined using a carbide end mill in brittle mode, producing numerous cracks; however, the roughness of the ceramic was similar to that of tool steel cut in ductile mode. Despite its rough surface, the bending strength of the machined Ti₂AlC was only slightly lower than that of polished Ti₂AlC. The cracks in the machined Ti₂AlC ceramics were induced with a kinking structure; however, they stopped at a length equivalent to one grain. The minimum strength of the machined Ti₂AlC ceramics with a fracture toughness of 6.9 MPa·m^1/2 was estimated by assuming a machining through-crack shape that was as deep as the maximum grain size. Cutting damage was limited to a single grain; thus, the bending strength of the machined Ti₂AlC was not significantly reduced.

In this study, single crystals of double-perovskite-type oxide Li_xLa_(1−x)/3TaO₃ (LLTaO) were successfully grown using the traveling solvent floating zone (TSFZ) method. The Ta-rich phase, which was precipitated in the crystals, was grown via the conventional floating zone (FZ) growth process, indicating that LLTaO behaved as an incongruent melt. For the TSFZ growth for solvents with a LiTa₃O₈ composition of 8 %, which is less than the LLTaO (x = 0.18) stoichiometric composition, the black grown crystals were homogeneous and crack-free, with a typical size of approximately 20 mm in length and 5 mm in diameter. The grown crystals turned colorless and transparent after being left overnight in the air at room temperature (about 25 °C). The Li concentration in the grown crystals was determined to be x = 0.086(1). This value is lower than the nominal composition (x = 0.18) of the feed owing to Li evaporation during the crystal growth. The ionic conductivities of the grown crystals along [110] and [001] were 2.8 × 10⁻⁵ and 1.8 × 10⁻⁵ S·cm⁻¹, respectively. The anisotropic parameter was determined to be 1.56 indicating that the ionic conductivity along the ab-plane is higher than that along the c-axis. Furthermore, the calculated activation energies along [110] and [001] were 0.29 and 0.34 eV, respectively.

We present a new approach for designing flexible energy storage capacitors using two-dimensional (2D) inorganic nanosheets. 2D dielectric Ca₂Nb₃O₁₀ nanosheet and ferroelectric poly(vinylidene fluoride) (PVDF) were selected as model material systems. Langmuir–Blodgett deposition was utilized for layer-by-layer engineering of (Ca₂Nb₃O₁₀/PVDF) nanocomposite films on an indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate. Such a new composite design realized the simultaneous improvement of energy density (∼7 J cm⁻³) and efficiency (∼78 %) even in the ultrathin form (∼20 nm) on the ITO-coated PET substrate. Nanosheet-based flexible capacitors also maintained a stable performance even after 10⁴ times bending cycles. These results indicate that our nanosheet approach is of technological importance for exploring new flexible dielectric capacitors.

Porous gallium oxide films were tried to synthesize at low temperatures. Ga nanoparticle dispersions were synthesized using ultrasound irradiation in 2-propanol and two films methods were considered. In the case of the spray coating of Ga nanoparticle dispersions and treatment with hydrazine vapor, Ga films were obtained. In the case of depositing Ga nanoparticles on a cover glass and aging them in hydrazine solution at a refrigerator temperature, porous γ-Ga₂O₃ film was synthesized. This new process of low-temperature aging in a refrigerator using hydrazine solution allows synthesizing porous γ-Ga₂O₃ film. Generally, the synthesis of oxide ceramics requires high-temperature processing, but this method allows oxidation at low temperatures, such as refrigerator temperatures, making it an energy-efficient process.

Photodegradation and accompanying oxidizing action of peroxotitanium complex (PTC) film were investigated, which made from PTC aqueous solution containing 61.3 mol % peroxo groups (O-O) to total Ti. The apparent activation energy (E_a) of the PTC degradation was revealed to be 132 kJ·mol⁻¹ (λ = 905 nm), according to Arrhenius plot of the degradation rate constant of PTC aqueous solution with microwave hydrothermal treatment at 100–180 °C. The PTC films were slowly decomposed by light irradiation of UV lamp, visible light LED or light bulb, and simultaneously oxidatively decomposed methylene blue dissolved in water. The oxidation reaction occurred even under the light of long wavelength around 900 nm closed to the E_a. Furthermore, the utilization efficiency of active oxygen generated by the photodegradation to the oxidation reaction of acetaldehyde gas was estimated to be 66 and 80 % under UV light (2.00 mW·cm⁻²) and LED visible light (1.50 mW·cm⁻²), respectively.

Interzeolite conversion (IZC) of zeolites has attracted significant attention; however, research on silicoaluminophosphate zeolite system is still in its early stages. Herein, an IZC of an FAU-type silicoaluminophosphate zeolite (SAPO-37) is performed using tetramethylammonium hydroxide (TMAOH) and piperidine as organic additives. For comparison, conventional hydrothermal synthesis using an amorphous precursor instead of SAPO-37 is also performed. Using TMAOH, SOD-type silicoaluminophosphate zeolites (SAPO-20) are obtained from both parent SAPO-37 and the amorphous precursor. However, in the case of piperidine, SAPO zeolites with different topologies are obtained from parent SAPO-37 and the amorphous precursor; that is, SOD-type SAPO-20 is obtained from parent SAPO-37, and CHA-type silicoaluminophosphate (SAPO-34) is obtained from the amorphous precursor. Piperidine molecules, as organic additives, are observed to be occluded in the cages of the obtained SAPO-20. The characteristics and thermal stability of the as-synthesized SAPO-20 are analyzed in detail.

This study used ultrasound irradiation to fabricate Zn²⁺-doped γ-Ga₂O₃ nanoparticles (NPs) from Zn–Ga alloy at near-room temperature (60 °C). The Zn²⁺-doped γ-Ga₂O₃ NPs were obtained at 60 °C after two steps of ultrasound irradiation (miniaturization and oxidation of Zn–Ga alloy). The specific surface area of Zn²⁺-doped γ-Ga₂O₃ NPs with a zinc content of 4 at.% was 90.4 m²/g. The oxidation behavior of Zn–Ga liquid alloy significantly differed from that of liquid Ga. X-ray photoelectron spectroscopy spectrum and lattice constant of Zn²⁺-doped γ-Ga₂O₃ confirmed Zn²⁺-doping into the γ-Ga₂O₃ crystal structure. By annealing at 900 °C, the obtained Zn²⁺-doped γ-Ga₂O₃ did not transform to Zn²⁺-doped β-Ga₂O₃ but to the mixed phase of β-Ga₂O₃ and ZnGa₂O₄. The results indicate that Zn²⁺ cations, with larger ionic radii than Ga³⁺ cations, are more difficult to be introduced into the β-Ga₂O₃ crystal lattice. Thus, this ultrasound process can potentially synthesize various metal cations-doped γ-Ga₂O₃ NPs without using high temperatures and pressures.

Spray freeze granulation drying (SFGD) is a granulation technique, involving the freezing of sprayed droplets, followed by freeze drying. This technique affords soft granules, which is advantageous for producing sintered bodies with few defects. However, non-spherical and/or hard granules are sometimes formed by SFGD, and the sintered body fabricated from such granules shows reduced density and strength. The formation of such non-spherical and/or hard granules is expected to be avoided by selecting an appropriate binder. Therefore, in this study, four types of binders (water-soluble acrylic polymer, acrylic emulsion, and poly vinyl alcohol with low and high degree of polymerization) were tested to produce alumina granules via SFGD. The shapes and properties of the granules, as well as densities and strength of the sintered bodies, were evaluated. By choosing a suitable binder, the formation of non-spherical granules can be significantly reduced, and soft granules are obtained. These leads to a sintered body with high density and high strength. The acrylic emulsion binder was found to be the best performing binder among the four binders.

The ordered arrangement of particles and holes in SiO₂ particle-accumulated films by small-angle X-ray scattering (SAXS) was investigated. The SAXS profiles of SiO₂ particles exhibited the typical oscillation shown by monodisperse spherical particles. On the other hand, the SAXS profile of the ordered SiO₂ particle-accumulated film showed an additional oscillation suggesting that another scattering component existed except for SiO₂ particles. Furthermore, considering two components: “SiO₂ in an air matrix” and “air holes in a SiO₂ matrix”, we successfully reproduced the SAXS profile of the ordered particle-accumulated film. The additional oscillation shows the existence of the tetrahedral holes, suggesting that this SiO₂ particle-accumulated film forms a close-packed structure. The intensity of the additional oscillation increased with the regularity of the particle arrangement in the SiO₂ particle-accumulating film. These results suggest that SAXS measurements using synchrotron radiation can provide information on the order of particle arrangement in composite films.

This study addresses the advantages of using a lanthanum fluoride (LaF₃) nanocrystals-based fluoride ion sensor. We propose a method that enables the preparation of fluoride ion-selective LaF₃ nanocrystals at low temperatures (less than 80 °C) in contrast to the conventional method, wherein high temperatures (1000 °C and above) are required for preparing a single-crystal LaF₃. An LaF₃ nanocrystal with a diameter below 5 nm in the (001) plane was synthesized and subsequently deposited on a Ti electrode. The sensor exhibited a selective response to fluoride ions. This process does not require high-temperature and vacuum equipment and conditions, thus enabling easy production of fluoride ion sensors.

Microstructural control of MgO–Al₂O₃–SiO₂ (MAS) glass-ceramic (GC) with precipitated enstatite (MgSiO₃) in the 0.68–12 µm range from a parent glass having one composition was achieved by using titanium oxides with varying particle sizes and crystallinities as nucleation agents. Specifically, compared with the MAS-GC prepared using TiO₂ with 50–200 nm and relative high crystallinity (TiO₂-L-H), the MAS-GC prepared by mixing TiO₂-L-H with TiO₂ having single nanometer size and relative low crystallinity displayed an increase in the average crystal particle size from 6.0 to 12 µm with the preservation of volume fraction. In addition, compared with the MAS-GC prepared using TiO₂-L-H, the MAS-GC prepared by TiO₂ having single nanometer size and relative high crystallinity exhibited a decrease in the average size of crystal particle from 6.0 to 0. 68 µm with a decrease in the volume fraction from 76 to 67 %. Therefore, these results indicated that the particle size and crystallinity of the raw glass materials are key parameters for controlling the microstructure of GCs.

Foamed ceramic is a novel lightweight wall material combining high strength, low density, and excellent thermal insulation. This study used coal bottom ash (CBA) to fabricate microporous foamed ceramics by the high-temperature foaming method. The CBA content and heating rate effects on the bulk density, compressive strength, pore structure, and phase components of foamed ceramics were systematically investigated. The results demonstrate that using CBA in foamed ceramics can effectively improve the green body foaming capacity. With the increased CBA content, the bulk density of foamed ceramics dropped, while the average pore size and shape factor increased, jointly reducing the compressive strength. Meanwhile, the quartz phase content decreased, and the mullite phase appeared gradually. The transition of the main crystalline phase from MgAl₂O₄ to Mg_0.7Fe_0.23Al_1.97O₄ with the increased CBA content gave rise to a change in the color of the foamed ceramic. The elevation in the heating rate can improve the foaming ability of the green body, contributing to increased porosity. However, the rapid heating rate of 10 °C/min results in an uneven pore size distribution in the foamed ceramics containing more than 70 wt % CBA. It increases the temperature difference in the sample, promoting a stratified distribution of pore size in samples with a CBA content of less than 30 wt %.

In the wet forming of ceramics, it is critical to control the cracking and deformation of the ceramic slurry during the drying process. This necessitates a comprehensive understanding of the changes in the internal structure of the slurry during the drying process using a high-resolution technique that enables direct and high speed observation. In this study, a combined system of optical coherence tomography (OCT) and thermogravimetry (TG) was developed for the operando observation of the evolution of the internal structure of a drying SiO₂ slurry. In the early stages of drying, the OCT signal intensity changed significantly owing to the Brownian motion of the SiO₂ particles in the slurry. The slurry was found to shrink as it dried and then lose its fluidity, and the ceramic particles were found to agglomerate from the surface. In the final stages of drying, localized dry regions developed in the vicinity of the slurry surface and expanded with drying. Crack formation was also observed in a part of the localized dry regions. Therefore, crack formation was attributed to inhomogeneous drying-induced shrinkage and stress generated in the drying object during the progression of localized drying. The novel operando observation technique using combined OCT-TG is successfully demonstrated to be an effective approach for understanding the internal structural changes in opaque slurries during their drying.