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Dielectric Measurements (dielectric + measurement)
Selected AbstractsOptical and dielectric studies on pure and Ni2+, Co2+ doped single crystals of bis thiourea cadmium chlorideCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2008R. Uthrakumar Abstract Good quality single crystals of Ni2+, Co2+ ions doped Bisthiourea Cadmium Chloride (BTCC) are some of the excellent and efficient non-linear optical materials grown from aqueous solution by slow evaporation method. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. UV spectral analyses on these samples reveal the improved transparency of the doped crystals ascertaining the inclusion of metal ion in the lattice. FTIR spectral analysis carried out on the materials confirm the presence of functional groups. Dielectric measurements reveal that the dielectric constant of pure and doped crystals decreases with increase of frequency. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Orientation and Dynamics of ZnO Nanorod Liquid Crystals in Electric FieldsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 12 2010Matthias Zorn Abstract ZnO nanorod polymer hybrids (i.e., ZnO nanorods coated with a block copolymer with a short anchor block (dopamine) and a longer solubilizing block of polystyrene (PS)) form liquid crystalline (LC) phases if they are dispersed at high concentration e.g., in a PS oligomer matrix. Due to the high mobility of the low Tg -matrix the nanorod polymer hybrids show a switching behavior under an applied AC electric field. Hence, the orientation of the nanorod mesogens can be changed from planar (parallel to the substrate) to homeotropic (perpendicular) in full analogy to the switching of low molecular liquid crystals in an electric field. Dielectric measurements show that such a switching is mainly due to the cooperative LC behavior, because the rods themselves exhibit only a very small effective dipole moment. The process can be investigated by polarizing microscopy. SEM images show the orientations of the individual nanorods, which correspond to the Fredericks transition well known for liquid crystals aligned in an electric field. This was the first time such a transition could be visualized by electron microscopy due to the large nanorod mesogens. The observation is interesting to orient nanorods perpendicular to an electrode and can help to improve optoelectronic devices. [source] Electrically Conductive Poly(DL -lactide)/Chitosan/Polypyrrole ComplexesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 12 2006Ying Wan Abstract Summary: The fabrication of novel conductive poly(DL -lactide)/chitosan/polypyrrole complex membranes is reported. Using poly(DL -lactide)/chitosan blends as matrices and polypyrrole as a conductive component, several kinds of membranes with various compositions are prepared. A percolation threshold of polypyrrole as low as 1.8 wt.-% is achieved for some membranes by controlling the chitosan proportion between 40 and 50 wt.-%. SEM images exhibit that the membranes with a low percolation threshold show a two-phase structure which consists of poly(DL -lactide) and chitosan phases. Dielectric measurements indicate that there is limited miscibility between the poly(DL -lactide) and chitosan but polypyrrole is nearly immiscible with the other two components. Based on the structural characteristics of the membranes, the polypyrrole particles are suggested to be localized at the interface between two phases. Dependence of conductivity of complex membranes on the PPy content. (,) PDLLA/PPy, (,) PDLLA/ch(10)/PPy, (,) PDLLA/ch(20)/PPy, (,) PDLLA/ch(30)/PPy, (,) PDLLA/ch(40)/PPy, and (,) PDLLA/ch(50)-PPy. [source] Dielectric monitoring of curing of liquid oligomer-modified epoxy matricesPOLYMER INTERNATIONAL, Issue 9 2001G Kortaberria Abstract Dielectric measurements were performed in ,real-time' at several temperatures to follow polymerization reactions on blends of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin with 4, 4,-diaminodiphenylmethane (DDM) hardener and different amounts of polyoxypropylenetriamine (POPTA) oligomer. These systems exhibit phase separation induced by molar mass increasing through curing of the resin. Monitoring of phase separation and vitrification (related to the ,-relaxation) was performed by this technique. The results are compared with those for the unmodified resin,hardener mixture. The change of the main ,-relaxation with cure time, cure temperature, and amount of modifier was measured for the mixtures. This change of the main relaxation through curing in the frequency domain was indicative of the cure reaction advancement, because of its dependence on the viscosity of the medium. The change of the ionic conductivity during curing was also analysed, showing its dependence upon cure temperature. © 2001 Society of Chemical Industry [source] Reversible phase transition of pyridinium-3-carboxylic acid perchlorateACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Heng-Yun Ye Pyridinium-3-carboxylic acid perchlorate was synthesized and separated as crystals. Differential scanning calorimetry (DSC) measurements show that this compound undergoes a reversible phase transition at ,,135,K with a wide hysteresis of 15,K. Dielectric measurements confirm the transition at ,,127,K. Measurement of the unit-cell parameters versus temperature shows that the values of the c axis and , angle change abruptly and remarkably at 129,(2),K, indicating that the system undergoes a first-order transition at Tc = 129,K. The crystal structures determined at 103 and 298,K are all monoclinic in P21/c, showing that the phase transition is isosymmetric. The crystal contains one-dimensional hydrogen-bonded chains of the pyridinium-3-carboxylic acid cations, which are further linked to perchlorate anions by hydrogen bonds to form well separated infinite planar layers. The most distinct differences between the structures of the higher-temperature phase and the lower-temperature phase are the change of the distance between the adjacent pyridinium ring planes within the hydrogen-bonded chains and the relative displacement between the hydrogen-bonded layers. Structural analysis shows that the driving force of the transition is the reorientation of the pyridinium-3-carboxylic acid cations. The degree of order of the perchlorate anions may be a secondary order parameter. [source] A porous-matrix sensor to measure the matric potential of soil water in the fieldEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2007W. R. Whalley Summary The matric potential of soil water is probably the most useful assessment of soil water status. However, the water-filled tensiometer (the benchmark instrument for measuring matric potential) typically only operates in the range 0 to ,85 kPa. In this paper, we report the development of a porous-matrix sensor to measure matric potential in the approximate range ,50 to ,300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of matric potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water-filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of matric potential when soil dried to matric potentials more negative than ,80 kPa. The porous-matrix sensors appeared to give reliable readings of matric potential in soil down to ,300 kPa and also responded appropriately to repeated wetting and drying. This porous-matrix sensor has considerable potential to help understand plant responses to drying soil. [source] Effect of lanthanum substitution on the Raman spectra of barium titanate thin filmsJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2007P. S. Dobal Abstract Thin films of Ba1,xLaxTiO3 on platinum substrates were synthesized using the sol,gel method for x values of 0.0, 0.03, 0.05, and 0.10, and the effect of trivalent La3+ substitution on the structural and dielectric properties was studied. Using X-ray diffraction, structural analysis of these compositions revealed a slight increase in the tetragonal distortion of the unit cell with increase in La content. Accordingly, an increase in the tetragonal to cubic transition temperature TT/C was detected by temperature-dependent Raman spectroscopy in the range of 70,500 K. Unlike the results from Raman scattering for the La-doped BaTiO3 films, the dielectric measurements showed broad and diffused dielectric maxima, making the estimation of the transition temperature merely qualitative. Copyright © 2006 John Wiley & Sons, Ltd. [source] Dielectric Tunable Properties and Relaxor Behavior of (Pb0.5Ba0.5)ZrO3 Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2008Xihong Hao Pb0.5Ba0.5ZrO3 (PBZ50) thin films with a thickness of about 500 nm in the paraelectric-phase were deposited on Pt/Ti/SiO2/Si substrates via the sol,gel process. The room-temperature dielectric measurements showed that the tunability and figure of merit (FOM) of the PBZ50 films at the maximum external DC field of 200 kV/cm were 39% and 38%, respectively. The results of temperature-dependent dielectric measurements confirmed that PBZ50 films had a typical diffuse phase transition characteristic and relaxor behavior. [source] Nonepitaxial Orientation in Sol,Gel Bismuth Titanate FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Paul Fuierer Control over crystallographic orientation in ceramic thin films is important for highly anisotropic structures. Layered perovskites, like Bi4Ti3O12, have interesting properties associated with their ferroelectric nature, which may be fully exploited only when films are highly textured. Textured films of this titanate were fabricated via a sol,gel technique without using epitaxial growth. Orientation in the film is confirmed by XRD and SEM, and supported by refractive index and dielectric measurements. In an attempt to explain the orienting effect, light scattering experiments were conducted to yield information about the molecular size, shape, and conformation of macromolecules as the sol,gel solution ages and condensation reactions proceed. These experiments clearly show an increase in the size of molecular clusters with time. We believe that it is the organization of these large clusters during spin coating, and the relationship of the backbone chemistry to the crystal structure of Bi4Ti3O12, that are responsible for the observed orientation. [source] Conductive Composites of Polyurethane Resins and Ionic LiquidsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2008Belinda Berns Abstract Composites of PUR and IL were prepared and specific conductivities and Shore A hardness were determined. IL were based on 1-alkyl-3-methylimidazolium salts with counterions BF, PF, triflate, or ethylsulfate. Presence of IL increased the conductivity by five orders of magnitude. Variation of alkyl chain length and nature of counterions only had little effect on the conductivity. Presence of IL had a plasticizing effect, which was most pronounced for the IL with dodecyl groups and PF as counterion. In broadband dielectric measurements, the complex conductivity showed a characteristic dispersion that is caused by the interplay between (hopping) transport of charge carriers and electrode polarization. [source] Dielectric in situ sensor monitoring of phase separation and changes in the state of each phaseMACROMOLECULAR SYMPOSIA, Issue 1 2003D. Kranbuehl Abstract Frequency dependent dielectric measurements have been used to monitor and characterize the phase separation process and changes in state of each phase. The measurements are made in situ using a micro planar sensor. They can be made both in the laboratory as well as in an industrial production or use environment. Two examples are presented. The first is monitoring the onset of phase separation, the buildup in Tg and change in composition of each phase during "reactive processing" of a high performance thermoplastic (TP) PPI, thermoset precursors (TS) DGEBA-MCDEA intially homogeneous blend. The second example involves monitoring the stability, onset of phase separation, as a function of temperature on a mineral oil, stearyl alcohol, water, sufactant emulsion used in the cosmetic industry. [source] Dielectric and calorimetric studies of ferroelectric phase transitions in Li(2,x)NaxGe4O9 crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005I. Cebula Abstract The ferroelectric phase transitions of LiNaGe4O9, Li1.1Na0.9Ge4O9, Li1.2Na0.8Ge4O9 and Li1.7Na0.3Ge4O9 crystals were studied. Experiments were carried out by means of classical dielectric measurements and using an AC calorimetric specific-heat measuring system. Critical behaviour is explained within Landau theory. The expansion coefficients of the state equation are determined. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural study of ferroelectric and paraelectric phases in PbK2LiNb5O15PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2004Y. Gagou Abstract The structures of PbK2LiNb5O15 showing the ferroelectricity below about 640 K have been studied in the paraelectric and ferroelectric phases by means of synchrotron X-ray powder diffraction. The data are analyzed with a Rietveld refinement method. It is found that the paraelectric structure and the ferroelectric one are of tetragonal and orthorhombic symmetry with P4/mbm and Pba2, respectively. The Pba2 structure gives a polar displacement along c -axis, whose direction is consistent with that deduced from dielectric measurements. The refined chemical occupancies of the cations Pb, K and Nb give the site-situation of these ions in the tunnels with square sections and pentagonal sections in each phase. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ChemInform Abstract: Discovery of New Ferroelectrics: [H2dbco]2·[Cl3]· [CuCl3(H2O)2]·H2O (dbco = 1,4-Diaza-bicyclo[2.2.2]octane).CHEMINFORM, Issue 32 2010Wen Zhang Abstract The title compound is characterized by temperature dependent dielectric measurements and XRD. [source] | ||||||||||||||||