Principles of equal-channel angular pressing as a processing tool for grain refinement

Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

In the paragraph following eq 28, the average bond valence was incorrectly referred to as V/R. It has been corrected to V/N. The paper originally posted to the web on September 3, 2009, and was reposted on September 24, 2009.

http://pubs.acs.org/doi/pdf/10.1021/cr900053k

Recent developments in the methods and applications of the bond valence model.

The integration of inorganic nanoparticles into polymers has been used for the functionalization of polymer materials with great success. Whereas in traditional polymer composites, micron sized particles or agglomerates typically cause significant light scattering hampering optical applications, in nanocomposites the particle dimensions are small enough for the production of highly transparent composites. A challenge for the generation of such materials is to develop an integrated synthesis strategy adapting particle generation, surface modification and integration inside the polymer. Surface grafting using polymerizable surfactants or capping agents allows for linking the particles to the polymer. Novel techniques such as in situ polymerization and in situ particle processing are beneficial to avoid aggregation of inorganic particles inside the polymer matrix. The functions associated with inorganic fillers are widespread. Layered silicates and related materials are nowadays commercially available for improving mechanical and barrier properties in packaging. With the availability of highly transparent materials, the focus has shifted towards optical functions such as luminescence and UV-protection in transparent polymers. IR-active fillers are used in laser-holography for transparent poly(methyl methacrylate) (PMMA) nanocomposites. Refractive index modulation and ultrahigh refractive index films were developed based on inorganic materials such as PbS. The integration of magnetic nanoparticles has a great potential for applications such as electromagnetic interference shielding and magneto-optical storage.This tutorial review will summarize functions associated with the integration of inorganic nanofillers in polymers with a focus on optical properties.

Functional inorganic nanofillers for transparent polymers

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The Nature Of The Chemical Bond

Microwave dielectric properties of A2+B6+O4 (A2+: Ca, Pb, Ba; B6+: Mo, W) ceramics were investigated as a function of packing fraction and bond valence. For A2+B6+O4 specimens sintered at 800–1100 °C for 3 h, a single phase with a tetragonal scheelite structure was detected, and the theoretical density was higher than 93% throughout the composition. Although the ionic polarizability of Ba2+ ion was larger than that of Ca2+ ion, the dielectric constant (K) of BaB6+O4 showed a smaller value than that of CaB6+O4. These results could be attributed to changes of the packing fraction due to the effective ionic size. The Q·f value was largely dependent on the packing fraction, as well as the percentages of theoretical density. The temperature coefficients of the resonant frequencies (TCFs) of the specimens were affected by the bond valence of oxygen. The specimens of CaMoO4 sintered at 1000 °C for 3 h showed the K of 10.8, Q·f of 76,990 GHz and TCF of −22.8 ppm/°C, respectively.

Effects of packing fraction and bond valence on microwave dielectric properties of A2+B6+O4 (A2+: Ca, Pb, Ba; B6+: Mo, W) ceramics

Microwave dielectric properties and far infrared reflectivity spectra were investigated in the (Zr0.8Sn0.2)TiO4 ceramics with 1 mol% Sb2O5, Sb2O3 and Nd2O3, respectively. Dielectric constant was not significantly changed, while the unloaded Q value was affected with additives. The unloaded Q of the pure (Zr0.8Sn0.2)TiO4 specimens was higher than that of the specimens with Sb2O3 and/or Nd2O3, but lower than that of the specimens with Sb2O5. The high unloaded Q value of 6600 at 7 GHz was obtained for the specimens with 1 mol% Sb2O5 due to elimination of oxygen vacancies. The effects of additives on the intrinsic microwave losses of the specimens were investigated by the infrared reflectivity spectra from 50 to 4000 cm-1, which were evaluated using the Kramers-Kronig analysis and classical oscillator model. The relative tendency of microwave dielectric properties calculated from the reflectivity data was in good agreement with the results by the Hakki and Coleman's method.

https://iopscience.iop.org/article/10.1143/JJAP.37.5367/pdf

Microwave dielectric properties and far infrared reflectivity spectra of the (zr0.8sn0.2)tio4 ceramics with additives

The temperature coefficient of the resonant frequency (TCF) of complex perovskite (Pb 1-x Ca x )[Fe 0.5 (Nb 1-y Ta y ) 0.5 ]O 3 ceramics (x = 0.5, 0.55; 0.0 ≤ y ≤ 1.0) was investigated, relative to the bond valence of the A- and B-site ions in the ABO 3 perovskite structure (such as the barium-, strontium-, and calcium-based complex perovskites). The TCF of these complex perovskite compounds varied with the bond valence of the A- and B-sites and the tolerance factor (t) in the perovskite structure. In the tilted region (t < 1.0), the tilting of the oxygen octahedra increased and the TCF decreased, because of the increased bond valence of the B-site. Also, the dependence of TCF on the bond valence of the A-site was similar to its dependence on t.

Relationship between the Bond Valence and the Temperature Coefficient of the Resonant Frequency in the Complex Perovskite (Pb1−xCax)[Fe0.5(Nb1−yTay)0.5]O3

The synthesis and dielectric study of BaTiO3/polyimide nanocomposite films

The dependence of microwave dielectric properties on the crystal structure, bond character, and electronic characteristics of AMoO4 and AWO4 (A = Ni, Mg, Zn) ceramics was investigated. The dielectric constant (K) of specimens was principally affected by the dielectric polarizabilities, molar volume, and electronic oxide polarizabilities. MgMoO4 and AWO4 (A = Ni, Mg, Zn) display a single phase monoclinic wolframite structure, whereas ZnMoO4 is a single phase triclinic wolframite structure. The quality factor (Qf) of AWO4 was higher than that of AMoO4 (A = Mg, Zn); these results were attributed to the packing fraction due to effective ionic size. The temperature coefficient of the resonant frequency (TCF) of the specimens was dependent on the cations' bond valence between the cation and oxygen ions. This suggests the ability to tailor ABO4 microwave K, Qf, and TCF via ionic design rules.

Eung Soo Kim

Papers

Effects of packing fraction and bond valence on microwave dielectric properties of A2+B6+O4 (A2+: Ca, Pb, Ba; B6+: Mo, W) ceramics

Microwave dielectric properties and far infrared reflectivity spectra of the (zr0.8sn0.2)tio4 ceramics with additives

Relationship between the Bond Valence and the Temperature Coefficient of the Resonant Frequency in the Complex Perovskite (Pb1−xCax)[Fe0.5(Nb1−yTay)0.5]O3

The synthesis and dielectric study of BaTiO3/polyimide nanocomposite films

Effects of Crystal Structure on the Microwave Dielectric Properties of ABO4 (A = Ni, Mg, Zn and B = Mo, W) Ceramics