In this paper, recent research development on realization of optical functions by controlling glass microstructures is briefly reviewed. Bi-doped glasses and transparent Ni²⁺-doped glass ceramics are introduced. The broadband infrared luminescence properties of these materials have been described. The luminescence mechanisms and their promising applications for broadband optical amplification and tunable lasers are discussed.

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In this study, nano-sized PbO-B₂O₃-SiO₂ glass powders were directly prepared by high temperature flame spray pyrolysis. Glass powders prepared at a low flow rate of fuel gas had bimodal size distributions of nano-sized and submicron-sized powders. However, nano-sized glass powders with a narrow size distribution were prepared via a chemical vapor deposition (CVD) process at a high flow rate of fuel gas as 4.5 L/min. The mean size of the glass powders formed by the CVD process was 38 nm. Nano-sized glass powders were found to have high transmittances above 83% at sintering temperatures between 480 and 520°C. On the other hand, transmittances of the dielectric layers formed from the glass powders with bimodal size distributions of nano- and submicron-sized powders decreased with a decrease of sintering temperatures. The dielectric layers formed from the nano-sized glass powders had a dense structure with no porous areas inside the layer at low sintering temperatures.

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Nano-crystalline MWO₄ (M = Ca, Sr and Ba) were successfully produced using cyclic microwave radiation in propylene glycol. XRD, TEM, SAED and EDX analyses revealed the presence of nano-crystalline MWO₄ containing the corresponding alkaline earth metals, W and O. Their lattice parameters and crystallite sizes were determined, and enlarged with the increase in the ionic radii of the corresponding divalent metals. Six different vibrations were detected using Raman spectroscopy and very strong W-O stretching of [WO₄]^2- tetrahedrons using FTIR.

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Hydrothermal preparation of a transparent wide-gap conductor Cd₃TeO₆ from CdO, TeO₂, H₂O₂, and alkali hydroxide was explored. The reaction without alkali hydroxide yielded only a small amount of Cd₃TeO₆, and NaOH gave a better yield than LiOH and KOH. The reactions without H₂O₂ did not form Cd₃TeO₆ at all. This observation indicated that H₂O₂ oxidized tellurium (IV) to the oxidation state VI in this system. The reactions at 240°C, the highest temperature available in this study, gave a better yield of Cd₃TeO₆ than the reactions at lower temperatures. After these optimizations, Cd₃TeO₆ was obtained as the dominant product.

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A visible light active TiO₂ photocatalyst was synthesized hydrothermally from an aqueous solution containing (NH₄)₂TiF₆ and NH₃ at 140 or 160°C. The prepared samples were characterized with X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and UV-Vis diffuse reflectance spectroscopy. The prepared samples showed obvious absorption in the wavelength range of 400-550 nm with a red shift in the adsorption edge. It was found that the prepared samples exhibited photocatalytic activity on degradation of methylene blue (MB) in water under visible light. The ion-doped TiO₂ obtained by hydrothermal treatment at 160°C for 7 d had the highest photocatalytic activity. The formation of Ti-N and Ti-F bonds was confirmed by X-ray photoelectron spectroscopy (XPS).

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Effect of structural characteristics on the dielectric properties of (Zn_1/3Ta_2/3)_0.5(Ti_1-xSn_x)_0.5O₂ (0.1 ≤ x ≤ 0.5) ceramics were investigated at microwave frequencies. The sintered specimens showed the solid solutions with the tetragonal rutile structure through the entire range of compositions. With the increase of SnO₂ content, the dielectric constant (K) and temperature coefficient of resonant frequency (TCF) were decreased with the decrease of dielectric polarizabilites and oxygen octahedral distortion, respectively. However, the quality factor (Qf) of the sintered specimens was increased with SnO₂ due to the reduction of Ti⁴⁺ ions and ordering of cations.

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This paper describes the preparation of several new transparent and very fine crystal glass-ceramics from the BaO-B₂O₃ system utilizing an appropriate additive of fluorides, partial replacement of B₂O₃ by SiO₂, and introducing nucleating agents, such as TiO₂. The physical properties of the prepared materials and the changes with varying base glass compositions and heat treatment programs were investigated. The thermal behavior and microstructure of the developed phases were characterized using DTA, XRD, and SEM. Glass-ceramics with marked transparency were prepared. These transparent derivatives owe their transparency to the distinctive properties of the nano-crystalline samples. The dielectric constant of transparent glass-ceramics samples at 100 kH_Z were between 14-20, which is very suitable for a wide range of applications, such as the high-speed switching of large-scale integrators. It was found that the addition of F^- and SiO₂ greatly influenced the transparency of the produced glass-ceramics. Also, the addition of TiO₂ greatly enhanced transparency, in spite of increasing cutoff in the UV region to a higher wavelength.

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Extending the investigations on Bi-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (1-x)(Bi_0.5Na_0.5)TiO₃-xBa(Zr_0.04Ti_0.96)O₃ [(1-x)BNT-xBZT] for x < 0.12. High density polycrystalline ceramics were fabricated using conventional solid-state processing methods. These ceramics are then taken for structure and properties measurements. A morphotropic phase boundary (MPB) between hexagonal (H) and tetragonal (T) was found at the composition 0.95BNT-0.05BZT with correspondingly enhanced dielectric and piezoelectric properties. Owing to the phase coexistence at the phase boundary, there exists a different symmetry regions (DSR) near the MPB. The DSR boundary motion increases the dielectric permittivity and piezoelectric coefficients. The planar coupling factor and piezoelectric constant are higher for compositions near the MPB. The effect of sintering time on the properties of 0.95BNT-0.05BZT ceramic was studied. Dielectric and piezoelectric properties have maximum values at the sintering temperature of 1100°C for 5 h. The dielectric constant (K^T₃₃) and electromechanical coupling coefficient (k_p) of 0.95BNT-0.05BZT ceramic were 850 and 34%, respectively. For 0.99(Bi_0.5Na_0.5)TiO₃-0.01Ba(Ti_0.96Zr_0.04)O₃ ceramics, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.14 and 0.51, respectively, at the sintering of 1100°C for 5 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 3.6. Our results show that (Bi_0.5Na_0.5)TiO₃-Ba(Zr_0.04Ti_0.96)O₃ solid solution ceramics are one of the promising lead-free ceramics for high frequency electromechanical transducer applications.

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The ⁵⁷Fe Mössbauer spectra of xLi₂O·2FeO·V₂O₅·P₂O₅ and xNa₂O·2FeO·V₂O₅·P₂O₅ glasses (x = 0, 0.5, 1.0 and 1.5) consist of two doublets due to Fe^II and Fe^III. The isomer shift indicates that Fe^III atoms form Fe^IIIO₄ tetrahedra or Fe^IIIO₆ octahedra, while Fe^II atoms from Fe^IIO₆ octahedra. A liner relationship exists between the glass transition temperature, T_g, and the quadrupole splitting, Δ, of Fe^III atoms in the Mössbauer spectra. Slopes of the straight lines were estimated to be 460 and 370°C (mm s^-1)^-1 in xLi₂O·2FeO·V₂O₅·P₂O₅ and xNa₂O·2FeO·V₂O₅·P₂O₅ glasses, respectively. These results suggest that Fe^III atoms form oxygenpolyhedra that are intermediate between Fe^IIIO₄ tetrahedra and Fe^IIIO₆ octahedra. The electric conductivity obtained by a dc four-probe method was of the order of 10^-5 to 10^-6 S cm^-1.

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We prepared single-phase Na_x(H₃O)_zCoO₂·y'H₂O with varying amount of Br₂ volume in acetonitrile, and examined the Na⁺ content (x), H₃O⁺ content (z), H₂O content (y') and T_c. By changing the amount of Br₂ during preparation, the amount of x in Na_x(H₃O)_zCoO₂·y'H₂O was controlled from 0.282 to 0.359. It was found that superconductivity is not correlated with Co valence but with y'/x, that is, the coordination number of Na⁺ with H₂O, and secondly with x⁄x+z, that is, the ratio of Na⁺ ion in the (Na⁺ + H₃O⁺) site, suggesting that shielding effect of Na_x(H₃O)_zCoO₂·y'H₂O governs superconductivity.

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Effects of manganese oxide (MnO) addition on the densification of Al₂O₃ during sintering were studied. Although MnO is commonly used as a sintering aid for Al₂O₃, it has not been used as a sintering aid to produce transparent alumina. High-density Al₂O₃ doped with slight MnO (> 99.5%) was obtained using a conventional powder processing method, with sintering at 1250°C for 24 h. The Al₂O₃- 0.05 mass%MnO exhibited optical total transmittance of 42% at 600 nm wavelength and three-point bending strength of 528 MPa. The transmittance was further improved to greater than 70% at 600 nm through hot isostatic pressing (HIP) after conventional sintering. The possibility of high-strength transparent alumina was demonstrated.

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The mechanical properties of yttrium aluminum garnet (YAG) ceramics were studied at the temperature range of 1100°C to 1250°C using three-point flexure tests. This experiment was conducted on YAG ceramics (YAG(A) and YAG(B)) having a different average grain size. YAG(A) had an average grain size of 1.04 μm, while YAG(B) had an average grain size of 1.54 μm. In the case of crosshead speed of 1 mm/min, YAG(A) and YAG(B) failed in a brittle manner at temperatures up to 1250°C, and had a strength of 500-600 MPa. In the case of crosshead speed of 0.0016 mm/min, YAG(A) failed in a brittle manner at temperatures up to 1100-1150°C, and had strength of 500-600 MPa, but exhibited plastic deformation at 1200°C. On the other hand, YAG(B) failed in a brittle manner at temperatures up to 1150-1200°C, and had strength of about 700 MPa, but exhibited plastic deformation at 1250°C.

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Fine-sized Gd_0.81Tb_0.19PO₄ phosphor particles with spherical shape, dense inner structure and narrow size distribution were prepared by spray pyrolysis. The morphologies and size distribution of the particles prepared by spray pyrolysis were affected by the types of spray solution. The Gd_0.81Tb_0.19PO₄ phosphor particles obtained from the aqueous spray solution had hollow inner structure and bimodal size distribution. However, the Gd_0.81Tb_0.19PO₄ phosphor particles obtained from the polymeric spray solutions with citric acid and polyethylene glycol had dense inner structure and narrow size distribution. The mean size of the particles obtained from the aqueous spray solution was 1.3 μm. On the other hand, the mean size of the particles obtained from the polymeric spray solution with citric acid and polyethylene glycol was 0.8 μm. The Gd_0.81Tb_0.19PO₄ phosphor particles obtained from the polymeric spray solution with citric acid and polyethylene glycol (PEG 400) had higher photoluminescence intensity under vacuum ultraviolet light than that of the phosphor particles obtained from the aqueous spray solution.

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A novel process for synthesis of ZnO nanocrystals from exfoliated layered hydroxide zinc benzoate nanosheets has been developed. In this process, first a layered hydroxide zinc benzoate compound was exfoliated into the layered hydroxide zinc benzoate nanosheets of elementary host layer of the layered compounds in ethanol solvent. This organic-inorganic hybrid nanosheet was transformed into ZnO nanocrystals under electron beam irradiation conditions. The exfoliation reaction of the layered compounds and the transformation reaction from the exfoliated nanosheet into ZnO nanocrystals were investigated using XRD, SEM and TEM analyses. In the structural transformation reaction from the nanosheet into the ZnO nanocrystals, first the benzoate ions on the nanosheet are degraded by electron beam, then the zinc hydroxide become unstable, and finally the nanosheet is dehydrated to ZnO nanocrystals. The ZnO nanocrystals prepared by this process have a crystal size of about 5 nm and high crystallinity.

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Lead-free piezoelectric ceramics (1-x)(Na_0.5K_0.5)NbO₃-xBi_0.5(Na_0.8K_0.2)_0.5TiO₃ (abbreviated as NKN-BNKT100x, with x ranges from 0 to 0.08 mol) have been synthesized by a conventional solid state sintering method. The effects of amount of BNKT-content on electrical properties and crystalline structures have been investigated. X-ray diffraction analysis showed that a morphotropic phase boundaries (MPB) between orthorhombic and tetragonal phases exists in the composition range of 0.05 < x < 0.06, near which the dielectric and piezoelectric properties are enhanced. The NKN-BNKT5 ceramics exhibits good properties (d₃₃ = 216pC/N, k_p = 41%, ε₃₃^T/ε₀ = 1315). These results indicate that NKN-BNKT100x ceramic is a promising lead-free piezoelectric candidate material.

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