Hexagonal-tetragonal co-existing barium titanate powders were prepared by reducing commercial barium titanate powders with their particle size of about 100 nm in a hydrogen atmosphere for 1 h at several temperatures, and the microstructures were observed. It was found that the hexagonal-tetragonal barium titanate powder had a co-existing hexagonal and tetragonal phase in a particle rather than a mixture of two phases in the powder. The hexagonal contents of about 0, 25, 50, 70, 85, and 100 wt % were obtained at temperatures of 1310, 1315, 1320, 1324, 1330, and 1333 °C, respectively. The hexagonal phase was returned to the tetragonal phase by annealing at 1200 °C in air. A model for the mechanism of a complete transformation of barium titanate polymorph from tetragonal/cubic to hexagonal phases is proposed.

The physics of the dielectric relaxations induced by dipole polarization and dc conductivity are clarified via conjoint analysis of various complex planes. Taking CaCu₃Ti₄O₁₂ ceramic as a model sample, a typical dielectric relaxation induced by dipolar polarization is presented in the low-temperature range of 123–163 K. An obvious relaxation peak can be observed in dielectric permittivity and electric modulus planes, however, the relaxation peak gets blurred when characterized in impedance and conductivity planes because it is strongly covered by static permittivity or optical frequency permittivity effect. In the high-temperature range of 433–473 K, no evident relaxation is found in permittivity and conductivity planes, while a new dielectric relaxation process induced by dc conductivity arises in impedance and modulus planes. The activation energies of the low-temperature and high-temperature relaxation peaks are 0.094–0.097 and 0.92–0.93 eV, which corresponds to the bulk defect and grain boundary defect of the CaCu₃Ti₄O₁₂ ceramic, respectively.

Molybdenum oxide (MoO₃)-containing iron phosphate (Fe–P) glasses with an analyzed Fe/P molar ratio of 0.41–0.43 and 0–43 mol % MoO₃ were prepared via a conventional melt-quenching method. The X-ray diffraction analysis revealed that all prepared samples had an X-ray non-crystalline state with a halo pattern. The dependency of the MoO₃ concentration on the glass transition temperature and water durability were evaluated. The water durability was examined in terms of glass plates with dimensions of 10 × 10 × 3 mm³ via a static leaching test at 120 °C for 72 h using ultrapure water. Raman spectroscopy was used for the analysis of the PO₄ Qⁿ structures (n = 0, 1, 2) and the Mo⁵⁺/Mo⁶⁺ species. The Fe–P glasses containing 8–17 mol % MoO₃ consisted mainly of PO₄ Q¹ structural units as well as both Mo⁵⁺O₆ distorted octahedra and Mo⁶⁺O₆ octahedra and a Fe-related polyhedra with a minimization of P–O–P and Mo–O–Mo bonds. These structural features were qualitatively related to the improved properties of both thermal stability against crystallization and water durability for the MoO₃-containing Fe–P glasses.

We have examined the initial-stage degradation of a Ni–gadolinia-doped ceria (GDC) cermet hydrogen electrode prepared on a GDC buffer layer of a stabilized-zirconia electrolyte supported cell during steam electrolysis operation at 800 °C. With use of an air reference electrode, the IR-free electrode potential E and ohmic resistance of the hydrogen electrode side (R_H2-side) were recorded. After a steam electrolysis operation at −1.0 A cm⁻² for 211 h, the R_H2-side increased appreciably, by 36 %, while the value of E was nearly unchanged. It was found via a depth-direction analysis with use of focused ion beam-scanning ion microscopy that the remaining percentage of Ni decreased to ca. 60 % in the layer between 1 and 3 µm from the top of the GDC buffer layer, followed by a further decrease to 42 % at 0.5 µm. Since this suggests a significant cathodic polarization within the thin reaction zone, an enlargement of the reaction zone, together with a stabilization of Ni contacting with GDC, could be essential to mitigate such a degradation.

With its low abundance in the Earth’s crust and high mining costs, metallic tellurium (Te) is a limited resource. In advanced material industries, it is irrecoverable from solid wastes. Hence, we investigated the hydrothermal treatment of a Bi–Te intermetallic alloy (BT-alloy) to develop an eco-friendly resource recovery technique for recovering metallic Te. High-purity (∼100 mass %) metallic Te powder can be directly recovered from BT-alloy powder (0.1 g) with H₂SO₄ solution (30 mL, 3.0 mol/L) at 200 °C for at least 20 h. With H₂SO₄ and heating, metallic Te was formed by the oxidation of Te²⁻ in the BT-alloy. In this study, we demonstrated for the first time that selective metal deposition by elemental extraction and oxidation from solid materials could be achieved with hydrothermal treatment. Therefore, hydrothermal resource recovery could be used to recover chemical resources, such as metals, directly from solid waste materials.

We introduce the additives effect in the molten salts such as commercially pure KNO₃ and polluted KNO₃. The results showed that in case of the commercial purity KNO₃, only KOH improved the compressive stress (CS) of ion-exchanged glasses up to ∼50 MPa, and the others additives did not make the CS improvement. Rather than the CS was diminished by additive contamination. In case of the contaminated KNO₃, the additives K₃PO₄, K₂CO₃, and K₂SO₄ successfully removed the impurities, Na⁺, Ca²⁺, Mg²⁺, by precipitating chemical compounds in molten bath and recovered the CS up to ∼97 %. X-ray diffraction (XRD) results proved how the harmful ions in molten salt was removed by adding additives.