Wyniki wyszukiwania - Biblioteka Nauki

1

Technical aspects of dielectric spectroscopy measurements of liquid crystals

100%

Perkowski P. , Łada D. , Ogrodnik K. , Rutkowska J. , Piecek W. , Raszewski Z.

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tom Vol. 16, No. 3

271-276

EN

The dielectric spectroscopy measurements were performed for antiferroelectric liquid crystalline mixture. For this purpose, the cells with ITO electrodes were prepared. It was found that it is not possible to detect some important relaxation modes in Sm A*, Sm C*, and Sm CA* phases. The own cell mode (related to cell properties, i.e., capacity and resistivity) covers the dielectric response of liquid crystalline medium. Dielectric measurements in cells with gold electrodes were done to show all possible relaxations in antiferroelectric liquid crystals (Lcs).

2

Analysis of the Phase Transitions in BNT-BT Lead-Free Ceramics Around Morphotropic Phase Boundary by Mechanical and Dielectric Spectroscopies

88%

Silva Jr P. S. , Diaz J. C. C. A. , Florêncio O. , Venet M. , M’Peko J. C.

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tom Vol. 61, iss. 1

17--20

EN

In this work, the syntheses and characterization by mechanical and dielectric spectroscopies of (1-x) Bi0.5Na0.5TiO3-xBaTiO3 (BNT-100xBT), with x = 0.05, 0.06 and 0.07, lead-free piezoelectric ceramics is reported. Ceramic samples of BNT-BT have been prepared by mixed-oxide method and then conventionally sintered. X-ray diffraction patterns of sintered samples, indicated for BNT-7BT the presence of tetragonal (P4mm) complex perovskite structure, whereas for BNT-5BT and BNT-6BT the samples exhibit a mixture of tetragonal (P4mm) and rhombohedral (R3c) crystalline phases, which reveal the presence of a morphotropic phase boundary (MPB) in the BNT-BT system. Measurements of internal friction, Q-1, and the storage modulus, E’, as a function of temperature at various frequencies were carried out in a Dynamic Mechanical Analyzer (DMA), in the temperature range from 0ºC to 600ºC. Dielectric profiles are recorded in the frequency range from 1kHz to 100kHz and the temperature range from room temperature to 475ºC. Mechanical loss spectra obtained for investigated compositions of BNT-BT samples showed different frequency-independent anomalies. Two main anomalies for BNT-5BT and BNT-6BT, observed around 100ºC and 430ºC were associated with the ferroelectric-antiferroelectric and antiferroelectricparaelectric phase transitions, respectively. The results obtained from mechanical loss measurements were supported by dielectric relaxation spectra. For BNT-7BT, outside the MPB, four different frequency-independent processes were observed.

3

Dielectric spectroscopy of liquid crystals : electrodes resistivity and connecting wires inductance influence on dielectric measurements

88%

Perkowski P.

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tom Vol. 20, No. 1

79-86

EN

Dielectric spectroscopy is a very useful experimental method for liquid crystal investigation. Electrodes made from indium tin oxide (ITO) or gold are widely used in measuring cells. During the dielectric spectroscopy measurements performed for smectic liquid crystalline mixture it was found that detection of some important relaxation modes in paraelectric SmA*, ferroelectric SmC* and antiferroelectric SmCA* phases for frequencies higher than 0.2–0.5 MHz is not possible. The measuring setup does not allow us to measure such relaxations due to its own dielectric response covering the dielectric response of liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to non-zero resistivity of electrode material or non-zero inductivity of connecting wires. In this paper, the new model was introduced. Its final equations show how to calculate parameters of relaxations observed in liquid crystals, from dielectric response of the empty and filled measuring cell. The experimental proof of strong influence of measuring setup properties on effective (measured) values of dielectric permittivities was shown.

4

Badanie izolacji silnika indukcyjnego przeznaczonego dla współpracy z pompą ciekłego metanu.

75%

Walczak K. , Graczkowski A. , Gielniak J. , Siodła K.

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tom Vol. 44, nr 18

77-80

PL

W artykule przedstawiono wyniki badań prototypowego silnika indukcyjnego o izolacji szkło-mika-epoksyd przeznaczonego do pracy z pompą ciekłego metanu w warunkach kriogenicznych. Badania prowadzono na pojedynczych cewkach oraz na prototypowym silniku. Ocena właściwości izolacji obejmowała przede wszystkim odporność na działanie niskiej temperatury oraz szoku termicznego. Badania przeprowadzono z wykorzystaniem spektroskopii dielektrycznej oraz pomiarów wyładowań niezupełnych.

EN

The paper presents results of investigation of the prototype inductive motor with a glass-mica-epoxy insulation assigned to work with a liquid methane pump in cryogenic condition. The investigation were carried out on single coils and the prototype motor. The assessment of insulation properties consisted of low temperature and temperature shock resistance. The investigations were done using dielectric spectroscopy and partial discharge measurement.

5

Badanie izolacji silnika indukcyjnego przeznaczonego do współpracy z pompą ciekłego metanu.

75%

Walczak K. , Graczkowski A. , Gielniak J. , Siodła K.

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tom Vol. 44, nr 18

402-405

PL

W artykule przedstawiono wyniki badań prototypowego silnika indukcyjnego o izolacji szklo-mika-epoksyd przeznaczonego do pracy z pompą ciekłego metanu w warunkach kriogenicznych. Badania prowadzono na pojedynczych cewkach oraz na prototypowym silniku. Ocena właściwości izolacji obejmowała przede wszystkim odporność na działanie niskiej temperatury oraz szoku termicznego. Badania przeprowadzono z wykorzystaniem spektroskopii dielektrycznej oraz pomiarów wyładowań niezupełnych.

EN

The paper presents results of investigation of the prototype inductive motor with a glass-mica-epoxy insulation assigned to work with a liquid methane pump in cryogenic condition. The investigation were carried out on single coils and the prototype motor. The assessment of insulation properties consisted of low temperature and temperature shock resistance. The investigations were done using dielectric spectroscopy and partial discharge measurement.

6

Analiza częstotliwościowa parametrów dielektrycznych jako narzędzie diagnostyczne materiałów na przykładzie układu izolacyjnego papier-olej.

75%

Graczkowski A. , Walczak K. , Gielniak J. , Ekanayake C. , Gubański S. , Mościcka-Grzesiak H.

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tom Vol. 44, nr 18

37-40

PL

W artykule przedstawiono możliwości wykorzystania spektroskopii dielektrycznej w badaniach właściwości materiałów. Zaprezentowano wyniki badań odpowiedzi dielektrycznej izolacji papierowo-o I ej owej w aspekcie oceny jej zawilgocenia i zestarzenia. Porównano parametry dielektryczne próbek preszpanu i papieru impregnowanego o różnym stopniu zawilgocenia i zestarzenia w różnych temperaturach.

EN

The paper presents applications of dielectric spectroscopy in investigations of materials properties. The results of dielectric spectroscopy investigations of oil-paper insulation was presented in aspect of moisture content and aging evaluation. Dielectric parameters of impregnated paper and pressboard of different moisture content and aging state was compared at various temperatures.

7

Spektroskopia dielektryczna cienkich warstw PTFE.

75%

Ziaja J. , Zubel Z.

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tom Vol. 44, nr 18

369-372

PL

W niniejszej pracy przedstawiono elektryczne właściwości cienkich warstw PTFE uzyskanych metodą polimeryzacji plazmowej. Wykonano pomiary współczynnika strat dielektrycznych tg delta, a także pomiary prądów przejściowych (absorpcji i resorpcji) w funkcji napięcia polaryzującego próbkę. Zastosowano metodę czasowej odpowiedzi w celu uzyskania niskoczęstotliwościowych charakterystyk współczynnika strat całkowitych i polaryzacyjnych. Stwierdzono istotny wpływ ładunku przestrzennego na badane krzywe.

EN

This paper presents a method for plassma-assisted deposition of PTFE thin films. Dielectric loss coefficient tg delta and transient currents (absorption and resorption) versus polarization voltage were tested. Low-frequency characteristics used by Hamon approximation method. The results confirmed the considerable influence of space charge on electrical properties PTFE thin films.

8

Study of the relaxor behaviour in Ba0.68Na0.32Ti0.68Nb0.32O3 ceramic

63%

Bąk W.

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2009

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tom Vol. 37, nr 1

24-27

EN

Purpose: The purpose of this work was to synthesize a new ceramic solid solution Ba0.68Na0.32Ti0.68Nb0.32O3 (BNTN32), as well as to measure and analyse its dielectric properties within the temperature range 123 K-473 K, where dielectrically active phase transition was supposed to occur. Design/methodology/approach: The new ceramic composition was prepared by means of conventional method. Dependence of phase transition features on temperature and frequency of measuring field were measured using dielectric spectroscopy method within the frequency range from 20 Hz to 1 MHz. Findings: The electric susceptibility along with temperature decrease generally rises up and has transient dispersion vanishing at about 230 K. At higher and low temperatures, frequency dependence of dispersion differs in character: at temperatures at ~400 K, low frequency values dominate. Dielectric energy losses are very high at ~high temperature, they decline down while temperature decrease, and at about 200 K range its frequency dependence is reversed and less scattered with maximum at ~150 K. The whole transition of ferroelectric - paraelectric (FE - PE) type can be described by means of Curie-Weiss law and it gets diffused character. Research limitations/implications: For modelling purposes the structure parameters of BNTN32 have to be measured by X-ray diffraction in order to establish the dielectric/structural activities of transitions taking place within used the temperature range. Additionally, dielectric measurements within broader frequency range up to 1.8 GHz will be performed. Originality/value: The new type of ceramic material was prepared with interesting dielectric properties. Dispersion reverse of energy losses activated thermally and low frequency memory of barium titanate (BT) transition effect visible at ~400 K is to be a subject of modelling further work.