1,720,986 research outputs found
Domain Size Dependence of Dynamic Behavior Domain in (Pb0.85La0.15)TiO3 Ferroelectric Ceramics
No full textDynamic behaviour of domains during poling by acoustic emission measurements in La-modified PbTiO3 ferroelectric ceramics
No full textIn order to study the dynamic behaviour of domains during poling, the acoustic emission (AE) characteristics of two La-modified PbTiO3 ferroelectric ceramics in which 90 degrees and 180 degrees domains were respectively dominant have been investigated. One sample was a 15 mol% La-doped ceramic with a high tetragonality ratio (c/a=1.021) and the other was a 24 mol% La-doped ceramic where the tetragonality ratio was close to unity (c/a=1.007). The acoustic emission behaviour of the former sample consisted of both burst as well as continuous emission, with the latter sample mainly showing continuous emission. Energy distributions made it possible to distinguish between the AE signals resulting from 90 degrees and 180 degrees domain switching. From the observed results, it was confirmed that most of the AE occurred due to 90 degrees domain switching. By introducing an alternative switching behaviour for the 90 degrees domains, the behaviour of the AE generation during poling could be explained
Effect of two-step sol-gel reaction on the mesoporous silica structure
No full textthe present study, we investigated the effects of two-step sol-gel reaction by abrupt pH change on the SBA-15 and mesocellular silica foams (MCF). Mesoporous silica was fabricated by using triblock copolymer templates (poly(ethylene oxide) and poly(propylene oxide)). The prepared silica structure was characterized by X-ray diffraction, transmission electron microscopy, and N-2 sorption experiment. Specifically, we prepared SBA-15 with long-range two-dimensional hexagonal arrangement of 3 to 6-nm feature spacing and MCF with larger pores of a few tens of nanometers. The pore size and ordering were influenced by pH change in a two-step sol-gel reaction and the concentration of organic solvent. Although well-ordered hexagonal arrangement of mesopores was prevalent in acidic conditions, the materials synthesized by a single-step reaction in neutral or basic conditions possessed gel-like structure without mesopores. However, the present two-step reaction (low pH sol-gel reaction followed by high pH reaction) not only produced mesoporous materials but also provided controllability of the pore size. In particular, mesoporous structures with pore sizes as large as those of MCF were successfully fabricated by the two-step reaction without using organic swelling agents. As expected, when xylene was added as a swelling agent, the pore size increased with the xylene/copolymer weight ratio. (C) 2003 Elsevier Science (USA). All rights reserved.This work has been supported partially by grants from
the Brain Korea 21 and IMT-2000 Projects. The authors
thank BASF for their kind donation of the Pluronic P123
block copolymer. The Korea Basic Science Institute is also
acknowledged for allowing us to use TEM (EM912, Carl
Zeiss)
shear-induced structure of semi-dilute aqueous micellar solutions of the cetylpyridnium chloride and additive effects
No full textEffect of tetragonality ratio on photo-induced domain switching in poled (Pb1-xLax)TiO3 ferroelectric ceramics
No full textThe effect of the tetragonality (c/a) ratio on photo-induced domain switching in (Pb1-xLax)TiO3 ferroelectric ceramics preliminarily poled at 1.5kVmm(-1) was investigated by measuring photovoltaic current and acoustic emission (AE) signals. Results of total increment of photovoltaic current (J (pv)), total AE event count and AE energy distribution showed that non-steady state behavior of J (pv) was dominantly dependent on the activity of 90 degrees domain switching during illumination. The activity of photo-induced domain switching was explained in terms of the coercive field and the space charge field. It was confirmed that the magnitudes of the space charge field and coercive field were found to be optimal for the photo-induced 90 degrees domain switching at a c/a of 1.021. (C) 2000 Kluwer Academic Publishers
Influence of nonequilibrium electrons on photovoltaic current and domain switching in poled (Pb0.85La0.15)TiO3 ferroelectric ceramics during illumination
No full textThe variations of photovoltaic current and acoustic emission (AE) event counts with experimental parameters were observed in (Pb0.85La0.15)TiO3 ferroelectric ceramics during illumination in the absence of external electric field. Both photovoltaic current and cumulative AE event counts increased with illumination time. These results could be explained to be associated with the increase in the remanent polarization due to the photoinduced domain switching which resulted from the space charge held established by photoexcited electrons trapped at the grain boundaries. The influence of the experimental parameters on the activity of photoinduced domain switching could be explained in terms of the mechanical strain energy, Delta G(a)(M), which acted as the energy barrier for domain wall motion and the energy associated with space charge held, Delta G(a)(SC), which stimulated domain wall motion
2D nano/micro hybrid patterning using soft/block copolymer lithography
No full textIn this work, we fabricated various 2D hybrid patterns with the feature resolution from micrometer to nanometer scale by using soft lithography and block copolymer lithography. Composite molds for the high-resolution with feature sizes from 135 nm to 50 mum were composed of a hard layer supported by soft PDMS layer. Polymer (PU) replica holes were made from the composite mold by replica molding. Block copolymers (PS-b-PMMA and PS-b-PI) were used as ink materials for the pattern smaller than 100 nm. UV and ozone etching was used for the selective removal of one block in the block copolymer. (C) 2003 Elsevier B.V. All rights reserved.This work was supported by the Brain Korea 21 program,
the IMT-2000 program and a grant (M102KN010001-
02K1401-00212) from Center for Nanoscale Mechatronics
and Manufacturing of 21st Century Frontier Research
Program
Rheological analysis of the gelation behavior of tetraethylorthosilane/vinyltriethoxysilane hybrid solutions
No full textThe gelation behavior of tetraethylorthosilane (TEOS) sol in the presence of a silane coupling agent vinyltriethoxysilane (VTES) was investigated experimentally. Specifically, the gel time and gel structure were analyzed by the theological multiwave test of Fourier transform mechanical spectroscopy (FTMS) for the mixtures of TEOS/VTES with various molar ratios at different temperatures. Gelation was accomplished through the sol-gel reactions of the silicon alkoxide TEOS in aqueous acidic solution. The results showed that, at elevated temperatures, the gel point was scattered and obscured by the noise in low frequencies owing to the enhanced thermal agitations. In this case, the statistical method was used to find the exact gel time. The activation energy of gelation and the gel exponent ranged from 25 to 30 kJ/mol and from 0.581 to 0.771, respectively, depending on the TEOS/VTES composition. The fractal dimension was estimated from the gel exponent and indicated the gel structure and that the TEOS/VTES solutions formed a relatively open and coarse gel structure.This work has been supported partially by a grant from the Korea
Science and Engineering Foundation. The authors appreciate also
a partial support from the Brain Korea 21 Project
Ultraviolet-nanoimprint of 40 nm scale patterns using functionally modified fluorinated hybrid materials
No full textPhoto-curable fluorinated organic - inorganic hybrid materials (F-hybrimers) present high modulus, low surface tension, low shrinkage, and high etching resistance. These are essential properties as a mould and as a resist for nanoimprint lithography (\NIL). In order to control the properties of the fluorinated hybrimer, in this study it is modified by the optimal addition of appropriate acryl monomers as a mould and as a resist material for NIL. Accordingly, the viscosity in terms of the resist material and the modulus in terms of the mould material are modulated ( low v F-hybrimer and flexible F-hybrimer). Finally, 30 - 40 nm half-pitch line patterns are imprinted, using identically modified F-hybrimer material systems as a mould and a resist.This research has been supported by the Korea Science and
Engineering Foundation (KOSEF; Grant No. R01-2003-000-
10125-0) and the Brain Korea 21 project
Nonsteady-state photovoltaic current and photoinduced domain switching in poled (Pb0.85La0.15)TiO3 and BaTiO3 ferroelectric ceramics
No full textIn (Pb0.85La0.15)TiO3 and BaTiO3 ferroelectric ceramics under illumination in the absence of an external electric field, we observed that photovoltaic current increased with illumination time. On the basis of the absence of pyroelectric current just after light-off and the acoustic emission (AE) signals detected during illumination, the nonsteady-state photovoltaic current behavior was attributed to the increase in remanent polarization, related to the increase in spontaneous polarization, and photoinduced domain switching, both of which resulted from the space charge field established by photoexcited electrons trapped at the grain boundaries. The influence of the poling field on the photoinduced domain switching activity could be explained in terms of the mechanical strain energy, which acted as the energy barrier for domain wall motion, and the energy associated with the space charge field which stimulated domain wall motion
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