Journal of the American Ceramic Society

Rödig, Thomas; Schönecker, Andreas; Gerlach, Gerald

doi: 10.1111/j.1551-2916.2010.03702.xpmid: N/A

Piezoelectric generators enable maintenance‐free power supply for integrated electronics in smart system applications. The majority of publications consider the aspect of power transfer electronics; however, the influence of the transducer materials was rarely described. Recently, material characteristics received increased attention from the ceramics community. We set the focus of the present paper to commercially available piezoelectric ceramics. Different figures of merit are derived from system analysis using electromechanical modeling. They allow for the description of typical load scenarios and commercial piezoceramics. Derived rules are expected to be helpful for guiding ceramic engineers and system designers to succeed in improved generator solutions.

Heo, Jong; Quan, Chengzhe

doi: 10.1111/j.1551-2916.2009.03469.xpmid: N/A

Photo‐induced phenomena in binary (PbO–Ga2O3) and ternary (PbO–Bi2O3–Ga2O3) heavy metal oxide glasses were investigated. A red shift up to ∼0.05 eV in the absorption edge of 75PbO–25Ga2O3 glass (mol%) was observed by illuminating the subbandgap light for 30 min. This shift was completely erased by the heat treatment near the glass transition temperature. Refractive index of the glass at 600 nm also increased ∼0.011 by the illumination. It is believed that the presence of lone‐pair electrons associated with Pb‐polyhedra is essential to realize a reversible photo‐induced effect in these oxide glasses.

Zhou, Haijun; Gao, Le; Wang, Zhen; Dong, Shaoming

doi: 10.1111/j.1551-2916.2009.03481.xpmid: N/A

ZrB2–SiC coating on C/C composites was prepared through vapor silicon infiltration process. The coated C/C composites showed excellent oxidation performance at 1500°C. Isothermal oxidation results showed that there was weight gain accompanied in the whole oxidation process and no evidence of oxidation of C/C composite substrate was observed. The thickness of coating increased from 120 μm to about 200 μm after oxidizing at 1500°C. Three distinct layers could be observed in the coating, namely, outer SiO2‐rich layer, middle ZrB2‐rich layer, and inner SiC‐rich layer. ZrB2 particles were coarsened after oxidation.

Riedel, Ralf; Toma, Liviu; Janssen, Enrico; Nuffer, Jürgen; Melz, Tobias; Hanselka, Holger

doi: 10.1111/j.1551-2916.2009.03496.xpmid: N/A

Piezoresistivity was found in silicon oxycarbide (SiOC) ceramics synthesized using a polymer‐to‐ceramic transformation process. A commercial polysiloxane, namely poly(methylsilsesquioxane), was used as the starting material. The SiOC ceramic synthesized at 1400°C exhibits high piezoresistivity, leading to strain sensitivities (k factors) of ∼145, while lower pyrolysis temperatures (1000°–1300°C) do not show a piezoresistive effect. Structural characterization by X‐ray diffraction in combination with micro‐Raman spectroscopy revealed that with increasing pyrolysis temperature, the content of free carbon in the X‐ray amorphous SiOC matrix increases without changes in the overall composition. Percolation effects related to the carbon‐based phase segregated from the SiOC matrix are responsible for the piezoresistivity analyzed in the SiOC ceramic.

Wu, Guangheng; Zhou, Hong; Zhou, Xiaoye; Qin, Ni; Bao, Dinghua

doi: 10.1111/j.1551-2916.2009.03495.xpmid: N/A

xBiAlO3‐(1−x)PbTiO3 (xBA–PT, x=0–0.1) solid solution thin films were prepared on indium tin oxide‐coated glass substrates using a chemical solution deposition method at an annealing temperature of 600oC, and the effects of bismuth aluminate (BA) content on the structural, dielectric, and ferroelectric properties of the thin films were investigated. Formation of the solid solution thin films has been confirmed by XRD and Raman analysis. The thin films crystallize in the perovskite structure without the formation of any detectable secondary phase. With increasing BA content, the thin films transform the tetragonal phase into a pseudocubic phase. When x is 0.08, the thin film exhibits high dielectric constant and large remanent polarization (2Pr) values, which are 384 and 58 μC/cm2, respectively. In addition, the dielectric loss and the leakage current density were considerably reduced by adding BA to the thin films.

Xue, Jianfeng; Dong, Manjiang; Li, Jun; Zhou, Guohong; Wang, Shiwei

doi: 10.1111/j.1551-2916.2009.03489.xpmid: N/A

Aluminum nitride (AlN) ceramics has been prepared by nonaqueous gelcasting in air and sintering in nitrogen atmosphere. The influence of pH and dispersant on the ζ potential of AlN–ethanol slurry was studied. And the rheological behavior of the slurry was evaluated to optimize the dispersant content and solid loading. Concentrated AlN slurry (53.8 vol%) with low viscosity was prepared using polyethyleneimine as the dispersant. Sorbitol polyglycidyl ether and tetraethylenepentamine were used as gelling and hardening agents, respectively. A green body with a relative density of 63.3% was obtained. After sintering at 1800°C for 4 h, AlN ceramics with a relative density of 99.6% and a thermal conductivity of 200 W·(m·K)−1 were produced.

James, Nijesh Kunnamkuzhakal; Ratheesh, Ravendran

doi: 10.1111/j.1551-2916.2009.03508.xpmid: N/A

Low‐temperature sinterable BaCe2(MoO4)4 ceramics were prepared through solid‐state ceramic route. X‐ray diffraction, laser Raman spectroscopy and scanning electron microscopy techniques have been used to investigate the structure and microstructure of BaCe2(MoO4)4 ceramics. The laser Raman study reveals distorted MoO42− tetrahedral networks in the unit cell of the BaCe2(MoO4)4 ceramics. The BaCe2(MoO4)4 exhibits a dielectric constant of 12.3, an unloaded quality factor of 3320, and a temperature coefficient of resonant frequency of −37 ppm/°C.

Joung, Mi‐Ri; Kim, Jin‐Seong; Song, Myung‐Eun; Nahm, Sahn; Paik, Jong‐Hoo

doi: 10.1111/j.1551-2916.2009.03504.xpmid: N/A

Li2CO3 was added to Ba2V2O7 ceramics at various contents up to 20 mol% to decrease their sintering time and temperature. The Li2CO3‐added Ba2V2O7 ceramics sintered at 750°C for 2 h had a dense microstructure with a high density. A liquid phase, which existed as an amorphous phase after cooling, was formed during the sintering due to the melting of Li2CO3 and aided the densification of the specimens. The 6.0 mol% Li2CO3‐added ceramic sintered at 750°C showed good microwave dielectric properties of ɛr=10.93, Q×f=74 513 GHz, and τf=−19.86 ppm/°C, indicating that the Li2CO3‐added Ba2V2O7 ceramic is a good candidate material for low‐temperature cofired ceramics.

Lim, Jaehyuk; Park, Sangho; Kang, Shinhoo

doi: 10.1111/j.1551-2916.2009.03507.xpmid: N/A

A (Ti,W)C solid‐solution powder was synthesized via high‐energy milling and carbothermal reduction of a TiO(OH)2, WO3, and graphite mixture. The phase evolution during the reduction of a system that contains TiO(OH)2 is discussed and compared with TiO2 systems in terms of the X‐ray diffractometry and thermogravimetric analysis results. It was found that the presence of water molecules in the hydrate system reduces the milling efficiency. However, there was no inhibitory effect on the reduction of the oxide mixtures or the synthesis of the (Ti,W)C.

Lin, Dabin; Li, Zhenrong; Zhang, Shujun; Xu, Zhuo; Yao, Xi

doi: 10.1111/j.1551-2916.2009.03501.xpmid: N/A

MnO2‐doped (K0.5Na0.5)NbO3 (KNN) single crystals were grown by high‐temperature solution method using K2CO3–Na2CO3 eutectic composition as flux. The effect of the manganese dopant on the dielectric, piezoelectric properties and the domain structure was investigated. The MnO2‐doped KNN crystals were found to exhibit higher piezoelectric coefficient d33 and dielectric permittivity ɛr when compared with pure KNN crystal, being on the order of 270 pC/N and 730, respectively, for manganese‐doped level at 0.5 mol%, with slightly reduced orthorhombic to tetragonal phase transition TO—T, and Curie temperature TC, being on the order of 193° and 416°C, respectively. The domain size of [001]‐oriented KNN–Mn crystal was found to be on the order of 5–13 μm at room temperature, smaller than that of the domain size observed in the pure KNN crystal (20–30 μm). The thermal depoling experiments were performed on the [001]‐poled KNN–Mn crystals, where the partial depolarization was found to occur at temperatures above 200°C, due to the phase transformation.