Hydroxyapatite (HAp) is a mineral component of vertebrate hard tissues, thus it assumes a pivot role as essential biomaterials for bone repair. The HAp crystal belongs to a hexagonal system, and has two types of crystal planes with different atomic arrangements: positively-charged calcium ions are packed mainly in the a(b)-plane, while negatively-charged phosphate ions and hydroxyl groups are packed mainly in the c-plane. In vertebrate long bone surfaces, HAp crystals have a c-axis orientation, which leads to the development of the a(b)-plane. On the other hand, in tooth enamel surface, HAp crystals have an a(b)-axis orientation, which results in the c-plane. However, the rationale behind the difference orientations between long bone and tooth enamel in different crystal planes remains poorly understood. Therefore, we would like to elucidate the effect of crystallographic anisotropy of HAp on its osteogenic functions. In particular, single-crystal HAp particles with preferred orientation to a(b)- and c-axes were successfully synthesized as the models to mimic bone and tooth enamel and by investigating the specific adsorption of acidic and basic proteins onto these particles, key understanding of bone regeneration process could be made toward developing bioceramics with life function. In addition, porous HAp ceramics with osteoinductivity and enhanced osteoconductivity properties was also developed using a(b)-plane-exposed HAp fibers to further explore the relationship. In this review, we will describe the development of bioceramics with life functions by harnessing the crystallographic anisotropy of HAp to provide greater insight on the biological properties of the resulting bioceramics, such as cell behavior in vitro and bone formation in vivo.

Tailoring the microstructure in ceramics is important for improving ceramic properties. There are many parameters for controlling the microstructure, such as grain size, grain shape, grain boundary, and second phase. Crystallographic orientation is a particularly important parameter because its properties depend on the axis of the crystal structure. Various techniques can be used to control crystallographic orientation. A strong magnetic field can be applied to control the orientation even in diamagnetic ceramics and can be combined with other processes for fabricating the controlled microstructure. Therefore, magnetic alignment was the technique focused on in this review.

Lead-free piezoelectric ceramic (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ + xSnO₂ (BCZT + xSnO₂, for short) (x = 0, 0.004, 0.008, 0.012 and 0.016) system with remarkable electrical properties was prepared via the solid state reaction method. The roles of SnO₂ addition on the structural and electrical properties were investigated. X-ray diffraction showed that the perovskite structure was formed in all components. SEM images indicated that the addition of SnO₂ promoted grain growth in BCZT + xSnO₂ ceramics. Dielectric measurement revealed that the temperature of orthorhombic-tetragonal phase transition moved towards to higher temperature, while the temperature of tetragonal–cubic moved to lower temperature for the sample. The variation degree of temperature has a close relationship with the SnO₂ concentration. The outstanding electrical properties was obtained (P_r = 8.98 µC/cm², E_c = 1.21 kV/cm, d₃₃ = 656 pC/N, and strain = 0.090 %) with the sample of x = 0.012. The enhanced properties indicated that the (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ + xSnO₂ ceramics are promising for lead-free practical applications.

The shrinkage behavior of barium titanate (BaTiO₃) green compacts during flash sintering with a square alternating current (AC) field including a zero-field duration (AC-pulse wave) was investigated. It was found that an AC-pulse wave is effective for the densification of BaTiO₃ green compacts without reduction and discharge, which is confirmed by transmission electron microscopy and electron energy loss spectroscopy. BaTiO₃ sintered polycrystal was obtained at a furnace temperature of 1000 °C by the optimal AC-pulse conditions of 285 V/cm at 250 Hz and a duty ratio of 30 %. A waveform with alternating polarity and the inclusion of a zero-field duration is shown to be possibly useful for flash sintering of oxide materials including altervalent cations.

We investigated photoluminescence (PL) and scintillation properties of Dy-doped tellurite glasses [80TeO₂–5Al₂O₃–(15 − x)BaO–xDy₂O₃ (x = 0.1–0.5)]. The Dy-doped tellurite glasses were prepared by the conventional melt-quenching method. In PL, all the Dy-doped tellurite glasses showed sharp emission peaks at approximately 575, 660 and 755 nm originated from the 4f–4f transition of Dy³⁺. The 0.5 and 1.0 % Dy-doped tellurite glasses exhibited high PL intensities under 450 nm excitation light. In scintillation, the Dy-doped tellurite glasses showed emissions peaking at approximately 485, 585 and 665 nm due to the 4f–4f transitions of Dy³⁺, and the 1.0 % Dy-doped tellurite glass exhibited the highest scintillation intensity. Furthermore, the PL and scintillation decay time constants of the Dy-doped tellurite glasses were about 12.6–367 and 30.2–248 µs, respectively. Theses decay time constants were typical values for the 4f–4f transition of Dy³⁺. In addition, the Dy-doped tellurite glasses showed moderate afterglow levels of about 289–751 ppm, and the afterglow level of the 1.0 % Dy-doped tellurite glass (289 ppm) was almost comparable to that of a commonly used inorganic scintillator Tl-doped CsI.

In this study, we developed a highly efficient photoluminescent glass from the design of a short–medium range structure and the photoluminescence (PL) of a fluoroborate glass. We investigated PL and the structures of BaMgBO₃F ceramics and the B₂O₃-added composition of glasses and glass-ceramics. The glass showed higher quantum yield (QY) than ceramic samples, i.e., the QY was 95 % for glass and 51 % for ceramics, by a 395 nm excitation. The glass can contain a large amount of emission centers with small concentration quenching, and 15 % Eu-doped glass exhibited higher PL intensity and QY than commercial Y₂O₃:Eu³⁺ phosphor. The origin of a high QY and small concentration quenching were investigated by the structural analysis. The glass structure was investigated using ¹⁹F- and ¹¹B-magic-angle spinning nuclear magnetic resonance, extended X-ray absorption fine structure of Ba K-edge, and high-energy X-ray diffraction. Moreover, the glass structure was simulated by molecular dynamics. It was found that the glass had a structural similarity with BaMgBO₃F crystal in the short-range order of B and Ba. The glass had a clear selectivity that B preferred to bind to O and Ba preferred to bind to F. The glass also exhibited unique medium-range ordering. Two types of Ba–Ba displacements were observed, which could be attributed to in-plane and out-plane layered displacements of the corresponding crystal, with the stacking structure of oxide–fluoride layers indicated by the radial distribution. The glass showed anion segregation, also similar to the layer-stacking structure of BaMgBO₃F. This made the low phonon sites coordinated with F compatible with the asymmetric sites derived from the oxide network segregation, resulting in high PL efficiency. The study results can contribute to the use of rare-earth ion-doped glasses in various applications such as laser and optical amplification, white light emitting diode (LED) lighting, and sensing technologies.

Investigating the correlation between glass structure and physical properties is important for development of novel functional materials. It is well known that the physical and structural parameters of glass depend on the preparation condition. Fictive temperature, T_f, is one of the standards of glass obtained from the super-cooled liquid state. Since the T_f value is defined using structural relaxation of overtone mode of Si–O–Si vibration, correlation of the T_f with the structural ordering at longer range is worthy for exploring. Here, we examine structural change of SiO₂ glass possessing different T_f values probed by the first sharp diffraction peak (FSDP) observed in X-ray diffraction data. By annealing of SiO₂ glass, i.e. decreasing of T_f, a sharpening of the FSDP is observed. Both structural periodicity and the correlation length of the FSDP decrease with increasing the T_f. It is suggested that increase of smaller structural units contributing to the FSDP is the origin of the increase of elastic modulus of SiO₂ glasses.

Alumina has long been known to enhance the strength of porcelain; however, the strengthening mechanism is not sufficiently understood. The strengthening in alumina-strengthened porcelain is examined on the basis of the change in thermal shrinkage of a porcelain matrix upon addition of various amounts of calcined talc. The improvement in flexural strength of the porcelain as a result of the alumina addition is enhanced with increasing difference in the thermal shrinkage between the alumina particle and the matrix. The rate of increase of the flexural strength as a function of the difference in thermal shrinkage is described by the extent to which the compressive prestress on the matrix increases the nominal tensile stress required for the fracture of the porcelain. However, the strengthening due to the internal stress is not sufficient to describe the actual strength of the porcelain. Further strengthening is achieved by the relatively large thermal shrinkage of alumina particles suppressing the formation and extension of microcracks around quartz grains in the glass phase of the porcelain.

First-principles energy band calculations are performed for Y₂BaCuO₅ (YBC211) with ferromagnetic and three types of antiferromagnetic (AFM) spin orderings, namely, A, C, and G. The most stable phase is found to be G AFM ordering (AFM_G_YBC211). The calculated magnetic moment at the Cu sites is almost identical to the experimental one reported in the literature. However, the energy bandgap is estimated to be only 0.55 eV. The valence band (VB) maximum locates on the S-Γ line and the conduction band (CB) minimum locates at the Γ point, suggesting that AFM_G_YBC211 is an indirect bandgap oxide. From the density-of-states analysis, the VB of AFM_G_YBC211 comprises mainly the Cu 3d and O 2p states. The lower CB comprises the Cu 3d states, whereas the upper CB is attributed mainly to the Y 4d, Ba 5d, and O 2p states. Furthermore, in the dielectric function calculation of AFM_G_YBC211, the ε₂(ω) curves exhibit very strong peaks for the yy and zz components at 0.87 eV, whereas the corresponding peak for the xx component is weak. This difference is attributed to the anisotropy of the momentum matrix elements between the VB and the lower CB.

Attention has recently been paid to oxyfluorides, one of the mixed anion materials, because they possess unique properties for many kinds of application fields. Because the general synthesis processes for oxyfluorides are based on troublesome methods, novel safe and facile processes are required. In this study, MoO₃ was solvothermally reacted with KF, RbF, and CsF at 200 °C to form potassium, rubidium, and cesium molybdenum oxyfluorides. The reaction of MoO₃ with KF and RbF led to the formation of K₃MoO₃F₃ and Rb₃MoO₃F₃ with a known structure, respectively, while the reaction of MoO₃ with CsF induced an unknown phase which should be Cs₃MoO₃F₃ with the similar structure to those of K₃MoO₃F₃ and Rb₃MoO₃F₃. A₃MoO₃F₃ (A = K, Rb, and Cs) has not been synthesized under liquid phase until now, and this research clarified this kind of the solvothermal reaction can lead to the formation of unique oxyfluorides at low temperature. In addition, Cs₃MoO₃F₃ was converted into Cs₃Mo₂O₆F₃ by treatment with methanol, suggesting the instability of Cs₃MoO₃F₃. This kind of conversion reaction from one oxyfluoride to the other oxyfluoride has not been reported, and the development of such chemical conversion may lead to the formation of new oxyfluorides.

A carbon nanotube (CNT) layer was fabricated on a glass surface through covalent bond formation between the CNT and a photoreactive silane layer that was constructed on the glass. The silane layer contains a chlorobenzyl group (–C₆H₄–CH₂Cl) and generates benzyl radicals upon ultraviolet light irradiation; the generated radicals smoothly attack the surface of the CNT to form covalent bonds. The X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy results revealed the generation of benzyl radicals followed by the formation of covalent bonds between the glass surface and CNT. The as-formed covalent bonds improved the adhesiveness of the CNT layer on the glass surface; further, it was observed that some heat was generated upon infrared light irradiation.