Papers by Keyword: Domain

Abstract: 3C-SiC islands were grown on atomically flat (111) 4H-SiC terraces and characterized by micro-Raman and FTIR. The islands initially have a triangular shape as defined by three {100} planes and over time evolve into hexagonal shaped islands. The triangular shape reveals the domain orientation of the island and is easily observed with an optical microscope. Examining 347 3C-SiC islands on 17 4H-SiC terraces we found that islands grown on the same terrace have the same domain orientation with 99.6% probability. The orientation of 3C-SiC islands grown on adjacent terraces was found to be close to random. This work confirms an orientation selection rule with high probability, suggesting that 3C-SiC can be grown without anti-phase domains or DPBs when grown on a single atomically flat 4H-SiC terrace, even when there are multiple nucleation sites.

Abstract: The magnetostriction and magnetic properties of electrical steel are depended on the external stress. In this paper, a noncontact magneostriction measuring system using laser displacement meter with high resolution of 10 nm has been built. The grain-oriented electrical steel with dimensions 500 mm × 100 mm × 0.3 mm was measured between 20 MPa and-20 MPa. The magnetostriction and magnetic properties were highly sensitively to stress. A clear relationship between power loss and magnetostriction under stress was found, and the underlying mechanism has been discussed.

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 (P_r) and the coercive field (E_c) 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.

Abstract: Lead-free (Ba_0.97Ca_0.03) (Zr_0.18Ti_0.82) 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.

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 (E_c) revealed that the fatigue life of the PZT with higher E_c is about one order of magnitude longer than that with lower E_c 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.

Abstract: Domains and size effect of Curie temperature in BaTiO₃ nanoceramics has been studied in this paper. We have calculated Coulomb interaction in a single domain of multi-domains BaTiO₃ grain, and obtained Curie temperature at various grain size. The results show that along with the grain size decreases, the change of Coulomb interaction depends on type of domains. 90 degree domains cause Coulomb interaction increase and Curie temperature moves to high temperature; 180 degree domains make Coulomb interaction weak and Curie temperature moves to low temperature. The results are compared with experimental data.

Abstract: CaCu₃Ti₄O₁₂ (CCTO) is a cubical perovskite phase and sintered ceramics exhibit very high dielectric constant at room temperature. The speculated origins of the high dielectric constant are the existence of insulative barrier layer at grain boundaries and domain boundaries which created an internal barrier layer capacitance (IBLC) at the microstructure of CCTO. The relation of grains and domains electrical resistance were studied in this work by using impedance spectroscopy (IS). A series of samples with different heat treatment temperature were tested to investigate their microstructure by using field emission scanning electron microscopy (FESEM). The grains and domains resistance was calculated from a wide frequency range of impedance complex plane measurement (100 Hz to 1 GHz). The FESEM and IS analyses showed the dependency of grains and domains resistance to average grains size of CCTO microstructure.

Abstract: This article reviews the theories and experiments on the macroscopic/nanoscopic scales, which indicate that nearly free electrons/holes appear at polarization discontinuities as a result of not only extrinsic mechanisms such as imperfections but also intrinsic mechanisms. We examine the consistency of these theories and experiments with conventional ones. Such electrons/holes lead to various novel properties of ferroelectrics and provide new insight into ferroelectricity, including fundamental issues such as the origin of ferroelectricity. This origin appears naturally compatible with the existence of multiferroicity.

Abstract: The glass-covered Co-rich amorphous wires was annealed by an applied stress during the current annealing process. The influence of stress and dc current annealing on the giant magneto-impedance (GMI) effect were investigated by the magneto-impedance. Our experiments showed that the magentic anisotropy is reduced by the annealing treatments, furthermore, the maximum GMI value is increased to 105 %.The GMI value is enhanced by increasing the outer domain volume and inducing a transverse anisotropy due to the changing of inner stress.

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.