The discovery of oxygen-ion conductivity and changes in the crystal-structure model of nondoped lanthanum silicate oxyapatites are reviewed from the researches which led to the discovery to current work. The oxygen-ion conductivity of lanthanoid silicate oxyapatites was discovered by Nakayama et al., during development of new oxide lithium-ion conductors. Although samples with compositions of LiRESiO₄ (RE = La, Nd, Sm, Gd, Dy) were initially reported to be single phases with the same crystal structure, the accurate crystal structure of LiRESiO₄ was not clarified until later. The crystal structure determined from X-ray diffraction patterns of LiLnSiO₄ was revised as oxyapatite by another group. The chemical composition of the crystal phases in LiRESiO₄ was also revised to RE₁₀Si₆O₂₅ and/or RE_9.33Si₆O₂₄. The discovery of oxygen-ion conductivity in these materials was confirmed when researchers noted that samples of RE₁₀Si₆O₂₅, specifically, the samples without lithium, are electrically conducting. Furthermore, very high oxygen-ion conductivity in the direction parallel to c-axis was discovered after single crystals of RE_9.33(SiO₄)₆O₂ (RE = Nd, Pr, and Sm) were successfully grown. The crystal structure and defect models were also altered after the discovery of oxygen-ion conductivity. Although numerous reports related to the electrical conductivity of La_9.33+x(SiO₄)₆O_2+3x/2 ceramics have appeared in the literature, clear dependences of the total conductivity on the cation nonstoichiometry (x) as well as the sintering temperature are still unclear because of large discrepancies in the reported data. Furthermore, the composition region, where the lanthanum silicate oxyapatite single phase is formed, is also still unclear because of the inconsistencies in the reported results.

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The study of lead-free low-melting sealing glass with properties such as low glass transition temperature (T_g), low softening temperature (T_s), good wettability on the substrate, is in process. One of the low-sintering lead-free glass compositions, the bismuth glass system is considered to be an alternative to lead oxide glass. Research on the development of lead-free low-melting sealing glass in ZnO–P₂O₅–Bi₂O₃ (ZPB) system was prepared and the effects of substitution of Bi₂O₃ for ZnO on the structural, thermal, and wetting properties of a sealing glass were studied. The changes in T_g, T_s and coefficient of thermal expansion (CTE) may reflect decreasing connectivity of the glass structure, due to the increasing Bi–O bonds. This structure changes have an effect on wettability on the substrate. The addition of higher amounts of Bi₂O₃ improved the wettability of the glass on the substrate. The ZPB glass, possessing properties of low T_g and good wettability, is suitable for low-to-mid temperature sealing applications.

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A tetramethylorthosilicate(TMOS)/ethanol solution was gelled together with BaTiO₃ nanoparticles or carbon nanoparticles. The wet gel was dried in supercritical carbon dioxide, resulting in aerogel nanocomposites with compositions in the range of BaTiO₃/SiO₂ = 1/100 to 20/100 and C/SiO₂ = 20/100 to 80/100. The bulk density of the aerogel obtained was in the range of 0.1 to 0.2 g/cm³, the porosity was about 95%, and the specific surface area was in the range of 400 to 700 m²/g. These values represent the characteristics of the aerogel. The relative permittivity and dielectric loss were respectively approximately 2 and 5 × 10⁻³ for the BaTiO₃-silica aerogel nanocomposite, and in the range of 5 to 10 and 0.012 to 0.4 for the carbon-silica aerogel nanocomposite.

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The microstructure and microwave dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1-x)Ca_0.6Sm_0.8/3TiO₃ ceramics system with B₂O₃ additions (1 wt %) prepared by the conventional solid state route were investigated. Doping with B₂O₃ (1 wt %) can effectively promote the densification and the dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1-x)Ca_0.6Sm_0.8/3TiO₃ ceramics. 0.5La(Mg_1/2Ti_1/2)O₃–0.5Ca_0.6Sm_0.8/3TiO₃ ceramics with 1 wt % B₂O₃ addition possesses a dielectric constant (ε_r) of 48, a Q×f value of 35,000 GHz (at 8 GHz) and a temperature coefficients of resonant frequency (τ_f) of 9.1 ppm/°C sintering at 1450°C.

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The prepared (Mg_1−xCo_x)₂(Ti_0.95Sn_0.05)O₄ (x = 0.01–0.009) ceramics are sintered at 1275–1425°C, the needed sintering temperatures of (Mg_1−xCo_x)₂(Ti_0.95Sn_0.05)O₄ ceramics slightly increased with the increase of Co⁴⁺ content. The sintering characteristics of (Mg_1−xCo_x)₂(Ti_0.95Sn_0.05)O₄ ceramics are developed by the X-ray diffraction patterns and SEM observations to find the influence of sintering temperatures and Sn⁴⁺ content on the crystal structure and the grain growth. The influence Co⁴⁺ content and sintering temperatures on the quality values (Q×f) and the temperature coefficient of resonant frequency (τ_f values) of (Mg_1−xCo_x)₂(Ti_0.95Sn_0.05)O₄ ceramics at microwave frequency are well developed in this study. As an optimal compose, (Mg_1−xCo_x)₂(Ti_0.95Sn_0.05)O₄ (x = 0.05) successfully demonstrated a dielectric constant of 14.70, a Q×f of 330,000 GHz and a temperature coefficient of resonent frequency value of −48.18 ppm/°C sintering at 1350°C.

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Mesoporous TiO₂ thin films containing Au nanoparticles were synthesized via sol–gel and evaporation-induced self-assembly processes. In this work, the effect of surfactant concentration on the pore structure of mesoporous TiO₂ thin films was investigated and Au nanoparticles were introduced to enhance the electrical conductivity of mesoporous TiO₂ without collapse of the pore structure. Pore structure was analyzed with small angle X-ray diffraction and grazing incidence small angle X-ray scattering. Crystallization of TiO₂ was analyzed with wide angle X-ray diffraction. Increased surfactant concentration led to a corresponding increase in the porosity of mesoporous TiO₂ thin films, but pore ordering in the mesoporous structure was still enhanced. The increasing rate of electrical resistivity associated with increased porosity was reduced in response to decreases in the electron scattering probability, which are strongly dependent on the pore ordering of mesoporous structures. Furthermore, the electrical conductivity of mesoporous TiO₂ composite thin films was enhanced by the incorporation of Au nanoparticles due to the surface plasmon effect of Au nanoparticles.

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Electrically and thermally conductive SiC ceramics were fabricated by hot-pressing β-SiC, 2 or 4 vol % TiN, and 2 vol % Y₂O₃ powder mixtures in a nitrogen atmosphere. X-ray diffraction data indicated that the specimens consisted mostly of β-SiC grains and traces of α-SiC and Ti₂CN clusters. Highly-conductive Ti₂CN clusters segregated between SiC grains contributed to reduce the electrical resistivity of the TiN-doped SiC specimens. The high thermal conductivity of the TiN-doped SiC specimens was attributed to the lack of solubility of Ti and Y in the SiC lattice and the suppression of a massive β→α phase transformation in SiC. The electrical resistivity and thermal conductivity of the SiC with 2 vol % TiN specimen were 2.4 × 10⁻³ Ω·cm and 174.1 W/m·K, respectively.

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