The combination of glass-forming oxides can induce phase separation at the atomistic level, particularly when a mixture involves both ionic and covalent bonds. In this study, we report physical properties of B₂O₃-substituted ZnO–P₂O₅ (ZP) glass and the substitution effect of B₂O₃ on the structure of ZP glasses via magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray diffraction, small angle X-ray scattering, positron annihilation spectroscopy and inelastic light scattering measurements. The ¹¹B and ³¹P MAS NMR results suggest that the coordination states of boron are affected by the number of bridging oxygen atoms in the substituted PO₄ chain structure of the ZP glass. At 5 mol % or less B₂O₃ substitution, an emerging of atomistic phase separation is not confirmed. On the contrary, at 10 mol % B₂O₃ substitution, three-coordinated boron formation is confirmed in ¹¹B MAS NMR in addition to a correlation between the BO_4/2 units. The substitution of a large amount of B₂O₃ confirmed the local coordination change of zinc cations in addition to the formation of a cluster-like structure in the low-Q region via small angle X-ray scattering.

Vanadium oxides have attracted a great deal of attention because of their good electrical and magnetic properties, in addition to their excellent optical properties. VO₂ undergoes a phase transformation from a tetragonal to a monoclinic structure at 341 K, leading to changes in its electrical and optical properties. We successfully produced oxygen-defective VO_2−x films with thicknesses of the order of several hundreds of nanometers on the surface of V metal foils heat-treated at 773 K for 4 to 20 h under an oxygen partial pressure of 10.13 Pa. The thickness and the grain size of the oxides increased with increasing holding time. High-angle annular dark-field scanning transmission electron microscopy observations indicated that the transformation from a tetragonal to a monoclinic structure was accompanied by an atomic displacement along the c- and a-axes of the tetragonal VO₂ structure and that the monoclinic VO₂ structure was distributed in nanodomains within the tetragonal VO₂ grain. The existence of a stable tetragonal structure at room temperature probably originates from suppression of the atomic displacements accompanying the transformation through the introduction of oxygen deficiencies. The diffuse reflectance of oxygen-defective VO_2−x films was less than 30 %, indicating the absorption of visible and near-infrared lights.

The primary objective of this study was to analyze the effects of fluoride treatment with cyclic variations in pH on the structure of stoichiometric hydroxyapatite (HAp), calcium-deficient HAp (CDHAp), and carbonated HAp (CHAp) powders. The structures of HAp, CDHAp, and CHAp before and after fluoride treatment were investigated using X-ray diffraction, Fourier-transform infrared, Raman, and nuclear magnetic resonance spectroscopic analyses. The fluoride treatment with cyclic variations in pH increased the calcium deficiency in HAp and CHAp but decreased in CDHAp. During fluoride treatment, fluoridated CDHAp or fluoridated calcium-deficient CHAp was formed on the surface of the HAp samples via dissolution and crystal growth, accompanied by the selective elution of component ions and partial substitution of OH⁻ groups in the HAp hexagonal lattice with F⁻ ions. No evidence of the formation of Ca(OH)₂ and OH⁻ groups outside the HAp crystal lattice was obtained. A new perspective on the formation of structured water at the surface termination of the OH columns (disordered region), with possible interactions with adsorbed water molecules or nonspecifically adsorbed F⁻ ions was provided. The top surface of the fluoridated CDHAp consisted of an amorphous fluoride-rich hydrated layer, which included calcium phosphate and CaF₂.

We have successfully developed a new bioactive borosilicate (4-4) glass fibers with increased silicon content and decreased boron content, fibers of which were prepared by a melt-blow method. In the present study, we evaluated the in vitro degradation and conversion behavior of 4-4 glass fibers using simulated body fluid (SBF) and compared the behavior with those of borate (13-93B3; B3) glass fibers. In addition, to evaluate the effects of 4-4 glass fibers on cellular activity, we compared the effects of 4-4 and B3 glass fibers on cell proliferation and osteogenic differentiation, as assessed using the mouse preosteoblastic cell line MC3T3-E1. Glass fibers were incubated in SBF at 36.5 °C. Weight loss by the 4-4 glass fibers was attenuated compared to that by the B3 glass fibers. Additionally, SBF incubated with the 4-4 glass fibers showed slightly higher pH values than did SBF incubated with the B3 fibers. An analysis of changes in the concentrations of various ions in SBF during these incubations suggested that the precipitates contained calcium and phosphorus. X-ray diffraction analysis detected the presence of apatite peaks at 7 days for both B3 and 4-4 glass fibers. Scanning electron microscope images showed hemispherical structures (heterogeneous nucleation) covering the entire surface of the 4-4 glass fibers after 3 days. Therefore, the formation of apatite on 4-4 glass fibers was superior to that on B3 glass fibers. Moreover, the cell proliferation and osteogenic differentiation of MC3T3-E1 cells in the presence of 4-4 glass fibers was enhanced compared to that in the presence of B3 glass fibers. Together, these results suggested that 4-4 glass fibers might be superior to B3 glass fibers for use as a bone substitute to address bone defects.

Spray drying (SD) and spray freeze granulation drying (SFGD) are the granulation processes of ceramic powder. Alumina green body made from SFGD granules via compaction has a relatively uniform structure without inter-granular pores, resulting in higher density and strength in the sintered body. This gives SFGD granules an advantage over SD granules. This study investigates the compaction pressure and sintering temperature of alumina granules produced by SD and SFGD. Using SFGD granules allows for the production of dense high-strength sintered alumina at lower compaction pressures and sintering temperatures. Even with higher compaction pressures applied to SD granules, the achieved sintered density falls short of that obtained with SFGD granules. These findings highlight the additional benefits of using SFGD granules over SD granules.

In this study, the effect of Al addition on the yellowness of V-doped ZrO₂ was investigated. V-, Al-, and (V,Al)-doped as well as pure ZrO₂ powders were prepared via complex polymerization, and their thermally decomposed products were characterized. The absorption edge of the V-doped ZrO₂ exhibited a red shift as the heating temperature increased. In addition, the intensity of the absorption peaks centered at approximately 350 nm increased when Al was added to V-doped ZrO₂. The yellowness parameter b* increased significantly when V was added to ZrO₂; however, the addition of Al to ZrO₂ did not improve b*. When Al was added to V-doped ZrO₂, the b* value was significantly higher than that when only V was added, particularly after calcination at 700 °C. Furthermore, it was found that V in V- and (V,Al)-doped ZrO₂ was primarily present as V⁵⁺ and partially V⁴⁺ using X-ray photoelectron spectroscopy.

The sodium-ion conducting sulfide electrolyte Na₃MS₄ (M is a group 15 central element) has been developed and is promising for solid-state battery applications. Na₃PS₄ is a standard electrolyte with moderate conductivity greater than 10⁻⁴ S cm⁻¹ and good ductility, which allows close solid-solid contact with active materials. The conductivity of Na₃SbS₄ is ten times higher than that of Na₃PS₄, and partial replacement of Sb with W significantly increases conductivity to a magnitude of 10⁻² S cm⁻¹. This electrolyte has a high tolerance to moisture, and the structure is resistant to hydrolysis without generating harmful H₂S gas. The group 15 element As, which is located between P and Sb in the periodic table, has not been studied in detail as an endmember of Na₃MS₄ electrolytes. Thus, we synthesized and characterized Na₃AsS₄. The cubic Na₃AsS₄ phase was directly obtained by a mechanochemical process and exhibited a high Na⁺ ion conductivity of 10⁻³ S cm⁻¹ at room temperature, higher than that of the tetragonal Na₃PS₄ phase. Humidity stability tests showed that the crystal structure did not change when exposed to moisture. Cubic Na₃AsS₄ is an important sulfide endmember of group 15 central elements, and further increases in conductivity are expected by optimizing its composition through elemental substitution.