Papers by Keyword: Domain

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Authors: W. Lu, Dai Ning Fang, Keh Chih Hwang
Authors: Yoichi Kigoshi, Saki Hatta, Takashi Teranishi, Takuya Hoshina, Hiroaki Takeda, Osamu Sakurai, Takaaki Tsurumi
Abstract: Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 μm on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 μm on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 μm. The field emission scanning electron microscope (FE-SEM) observations revealed that the 90º domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 μm, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.
Authors: Zhi Hui Ge, Tao Shen Li, Lin Li
Abstract: In manufacturing grid, trust management is the core component, which is associated with resource sharing, role assignment etc. How to compute and evaluate the recommended trust is very important for cooperation among resource entities coming from different domains. In order to resolve the problem, a two-layer domain structure is constructed to organize the distributed cross-domain cooperation and the corresponding trust value evaluation algorithm is designed based on the structure. At last, an application prototype is developed to show the validity and the practicability of the proposed method.
Authors: Jun Ma, Zhi Ying Wang, Jiang Chun Ren, Jiang Jiang Wu, Yong Cheng, Song Zhu Mei
Abstract: The existence of trusted subjects is a major complication in implementing multilevel secure (MLS) systems. In MLS, trusted subjects are granted with privileges to perform operations possibly violating mandatory access control policies. It is difficult to prevent them from data leakage with out too strict confinement. This paper reconsiders the privilege from the view of sensitive data and presents a dynamic trusted domain (DTD) mechanism for trusted subjects. In DTD, a domain is associated with a special label structure (LabelVector) distinguishing security policies and builds an isolated environment based on virtualization for a certain trusted subject. The channel for the trusted subject to communicate with outsider is controlled by a trusted request decision maker (TRDM). Only the request satisfies the rules on domain label and security levels can be passed through.
Authors: Toshio Ogawa, Masahito Furukawa, Takeo Tsukada
Abstract: Poling characteristics, especially DC poling field (E) dependence of dielectric and piezoelectric properties were investigated to evaluate the domain behavior in lead-free ceramics such as alkali niobate and alkali bismuth titanate ceramics. The domain switching was confirmed by the E to realize minimum dielectric constant (εr), minimum electromechanical coupling factor (k) and maximum frequency constant (fc), because of domain clamping. On the other hand, the domain rotation occurred at the E to obtain maximum εr and minimum fc. These phenomena are observed in the lead-free ceramics as well as PZT ceramics.
Authors: Jian Shao, Xiang Yun Deng, Xiao Long Zhang
Abstract: Lead-free (Ba0.97Ca0.03) (Zr0.18Ti0.82) O3 (BCZT) ceramic is prepared by sol-gel technique. The sample shows a pure perovskite structure through the XRD pattern. Well-developed grain morphology and a dense microstructure are acquired at an optimistic sintering temperature (~1330°C). The BCZT ceramic shows a surprisingly high piezoelectric coefficient of d33=675 pm/V. The switching current curves are acquired in the different external fields by TF-2000 Ferroelectric Analyzer. It is found that with increasing the temperature, there is a decrease in the coercive field (Ec), and with increasing the electric field, there is an increase in the switching current obviously. Sintering temperature has an effect on switching current. The effect of temperature and electrical field on switching current is analyzed from viewpoint of the energy.
Authors: Motonori Nakamura, Chiharu Sakaki, Masahiko Kimura, Takehiro Konoike, Hiroshi Takagi, Kaori Shirakihara, Hirohisa Kimachi, Kesisuke Tanaka
Abstract: Fatigue tests on lead zirconate titanate (PZT) were performed by using single-edge-V-notched specimens under cyclic mechanical loading with or without superposition of a DC electric field. Fatigue life was prolonged by applying a DC electric field to the PZT ceramics. To estimate the domain contribution, fatigue tests on barium strontium titanate (BST) ceramics in both ferroelectric and paraelectric phase were carried out. The fatigue life of the ferroelectric phase was much shorter than that of the paraelectric phase. Comparing the fatigue lives of two PZT ceramics with different values of coercive electric field (Ec) revealed that the fatigue life of the PZT with higher Ec is about one order of magnitude longer than that with lower Ec when the stress-intensity factor of fatigue test is low. It is therefore concluded that non-180°domain switching probably deteriorates the fatigue life of ferroelectric ceramics.
Authors: Shao Peng Zhang, Xiao Hui Wang, Long Tu Li
Abstract: (1-x)BiScO3-xPbTiO3 (BSPT) ceramics with grain size range of 0.5~2.5 μm at morphotropic phase boundary (MPB) were prepared by conventional sintering method. The grain sizes of the ceramics were determined by scanning electron microscopy (SEM). The grain size effects on the structure of BPST ceramics were analyzed by X-ray diffraction (XRD). The ferroelectric hysteresis response under various uniaxial compressive stress of up to 150 MPa was measured. With increasing the mechanical uniaxial stress, the remnant polarization (Pr) and the coercive field (Ec) were significantly reduced. The direct current (DC) bias dependence of capacitance of MPB-BSPT ceramics with different grain sizes was compared. The results indicated that the domain switching was prevented by the compressive stress. The domain size and domain structure were influenced by the grain size. The domain switching under uniaxial stress and electric field became more difficult due to the decrease of grain sizes. The grain size as well as the domain size played a key role in the properties under external uniaxial compressive stress and electric field.
Authors: Min Jin, Hui Shen, Jia Yue Xu
Abstract: In the present work, a pulling down method was introduced to prepare the KNbO3 crystals and the growth results were evaluated. It was found the Pt crucible with 60° cone angle and folds at the seed well was helpful to obtain KNbO3 crystal with nice integrity. The blue color occurred on the top of KNbO3 ingot was confirmed to be orthorhombic KNbO3 by XRD analysis. Some complex domain structures, including 60°, 90° and 180° domains, were happened in the crystal which were attributed to phase transitions when it was cooled down to room temperature.
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