Multilayer ceramic capacitor (MLCC) production and sales figures are the highest among fine-ceramic products developed in the past 30 years. The total worldwide production and sales reached 550 billion pieces and 6 billion dollars, respectively in 2000. In the course of progress, the development of base-metal electrode (BME) technology played an important role in expanding the application area. In this review, the recent progress in MLCCs with BME nickel (Ni) electrodes is reviewed from the viewpoint of nonreducible dielectric materials. Using intermediate-ionic-size rare-earth ion (Dy2O3, Ho2O3, Er2O3, Y2O3) doped BaTiO3 (ABO3)-based dielectrics, highly reliable Ni-MLCCs with a very thin layer below 2 µm in thickness have been developed. The effect of site occupancy of rare-earth ions in BaTiO3 on the electrical properties and microstructure of nonreducible dielectrics is studied systematically. It appears that intermediate-ionic-size rare-earth ions occupy both A- and B-sites in the BaTiO3 lattice and effectively control the donor/acceptor dopant ratio and microstructural evolution. The relationship between the electrical properties and the microstructure of Ni-MLCCs is also presented.

https://iopscience.iop.org/article/10.1143/JJAP.42.1/pdf

Base-Metal Electrode-Multilayer Ceramic Capacitors: Past, Present and Future Perspectives

The rate of the resistance degradation of doped SrTiO3 ceramics is investigated as a function of various external and material parameters. The effects of the mutually interrelated parameters dc voltage, dc electric field, and thickness of the dielectric are described by power laws. Electron microscopic potential contrast studies show a Maxwell-Wagner polarization leading to a concentration of the electric field at the grain boundaries during the degradation. Based on this finding, the voltage step per grain boundary, ΔΘgb, is introduced as a rate-determining parameter which allows an explanation of the influence of the grain size on the degradation rate as well as the difference in the power laws for ceramic and single-crystal samples.

dc Electrical Degradation of Perovskite-Type Titanates: I, Ceramics

A large number of polycrystalline materials, both manmade and natural, display preferred orientation of crystallites. Such alignment has a profound effect on anisotropy of physical properties. Preferred orientation or texture forms during growth or deformation and is modified during recrystallization or phase transformations and theories exist to predict its origin. Different methods are applied to characterize orientation patterns and determine the orientation distribution, most of them relying on diffraction. Conventionally x-ray polefigure goniometers are used. More recently single orientation measurements are performed with electron microscopes, both SEM and TEM. For special applications, particularly texture analysis at non-ambient conditions, neutron diffraction and synchrotron x-rays have distinct advantages. The review emphasizes such new possibilities. A second section surveys important texture types in a variety of materials with emphasis on technologically important systems and in rocks that contribute to anisotropy in the earth. In the former group are metals, structural ceramics and thin films. Seismic anisotropy is present in the crust (mainly due to phyllosilicate alignment), the upper mantle (olivine), the lower mantle (perovskite and magnesiowuestite) and the inner core (e-iron) and due to alignment by plastic deformation. There is new interest in the texturing of biological materials such as bones and shells. Preferred orientation is not restricted to inorganic substances but is also present in polymers that are not discussed in this review.

http://iopscience.iop.org/article/10.1088/0034-4885/67/8/R02/pdf

Texture and anisotropy

We present a comprehensive thermodynamic and kinetic analysis of the suitability of cerium oxide (ceria) for thermochemical fuel production. Both portions of the two-step cycle, (i) oxygen release from the oxide at 1773 and 1873 K under inert atmosphere, and (ii) hydrogen release upon hydrolysis at 1073 K, are examined theoretically as well as experimentally. We observe gravimetric fuel productivity that is in quantitative agreement with equilibrium, thermogravimetric studies of ceria. Despite the non-stoichiometric nature of the redox cycle, in which only a portion of the cerium atoms change their oxidation state, the fuel productivity of 8.5–11.8 ml of H2 per gram of ceria is competitive with that of other solid-state thermochemical cycles currently under investigation. The fuel production rate, which is also highly attractive, at a rate of 4.6–6.2 ml of H_2 per minute per gram of ceria, is found to be limited by a surface-reaction step rather than by ambipolar bulk diffusion of oxygen through the solid ceria. An evaluation of the thermodynamic efficiency of the ceria-based thermochemical cycle suggests that, even in the absence of heat recovery, solar-to-fuel conversion efficiencies of 16 to 19 per cent can be achieved, assuming a suitable method for obtaining an inert atmosphere for the oxygen release step.

A thermochemical study of ceria: exploiting an old material for new modes of energy conversion and CO2 mitigation.

The formation of densely crosslinked networks by chain crosslinking photopolymerization is discussed in relation to selected applications in the electronics industry. All of these applications make use of the high speed and of the latitude to meet other requirements by variation of the chemical structure of the monomers. The selection comprises:

1.

The coating of optical fibers;




2.

The replication of optical discs;




3.

The replication of aspherical lenses, used for laser read-out of these discs.

Network formation by chain crosslinking photopolymerization and some applications in electronics

The effects of additions of La2O3 and La2O3-3TiO2 on the electronic properties of barium titanate have been investigated. It has been found that small additions of these components markedly increase the lifetime of this material subjected to dc fields of 50 v per mil at 200°C.

Stabilized Barium Titanate Ceramics for Capacitor Dielectrics

Semiconducting barium titanate has been prepared both by coprecipitating the lanthanum in the preparation of barium titanyl oxalate and by precipitation of lanthanum hydroxide in a slurry of the titanate. Partial substitution of strontium or lead for barium and zirconium for titanium has also been achieved using this oxalate process. The electrical conductivity of these materials was measured and is discussed. The effect of excess titanium on the electrical properties was also determined and an excess of 1 to 2 mole % was found to raise the positive temperature coefficient under the firing conditions employed.

Preparation of Semiconducting Titanates by Chemical Methods

Laser‐drawn epoxy‐acrylate‐coated fused silica fibers (∼110 μm fiber diameter) have been produced with high and exceptionally uniform strength. When tested in 20‐μm lengths, they show a single‐moded Weibull distribution, (m∼25), a median tensile strength Sm of 750 ksi (5.25 GN/m2), and a coefficient of variation (ν) of about 0.04. Using the previously justified ’’weakest link’’ model, this predicts Sm∼600 ksi (4.2 GN/m2) for l‐km gauge lengths. The measured strength of a 1680‐m‐long fiber (i.e., the minimum strength found in testing 84 20‐m lengths) is 620 ksi (4.35 GN/m2). The capability of drawing kilometer lengths of fibers with strengths of this magnitude and uniformity is extremely important for the production of optical fiber cables.

Epoxy‐acrylate‐coated fused silica fibers with tensile strengths ≳500 ksi (3.5 GN/m2) in 1‐km gauge lengths

Tensile strength measurements have been made on coated fused silica fibers at gage lengths up to 50 m. At gage lengths between 0.04 and 10 m, the average strength is essentially constant at about 5 GN/m2 (700 ksi). At gage lengths greater than 20 m the length dependence becomes important and by 50 m the strength has decreased to about 2 GN/m2 (300 ksi). The minimum strength recorded in the testing of samples taken continuously from a length of 1031.6 m was 0.43 GN/m2 (64 ksi). A ’’weakest link’’ model appears to be obeyed.

Strength of 0.04-50-m lengths of coated fused silica fibers

The degree of preferred orientation (texture) of doctor-bladed polycrystalline 99.5% Al2O3 substrates from 3 sources was evaluated by qualitative optical and quantitative X-ray analyses. The substrates exhibit a fiber texture in which the basal planes lie preferentially in the plane of the substrate. The same texture is weakly evident in the unfired materials. The strength of the texture in fired substrates varies from lot to lot and among suppliers, but its character remains essentially the same. Measurements of dielectric constant, flexural strength, and thermal expansivity are consistent with the observed texture. The possible origins of the texture and its importance in substrate applications are discussed.

F. V. DiMARCELLO

Papers

Stabilized Barium Titanate Ceramics for Capacitor Dielectrics

Preparation of Semiconducting Titanates by Chemical Methods

Epoxy‐acrylate‐coated fused silica fibers with tensile strengths ≳500 ksi (3.5 GN/m2) in 1‐km gauge lengths

Strength of 0.04-50-m lengths of coated fused silica fibers

Preferred Orientation in Al2O3 Substrates