Wyniki wyszukiwania - BazTech

1

Investigation of new chiral fluorosubstituted compound exhibiting room temperature antiferroelectric phase

Czerwiec J. M., Żurowska M., Garbat K., Dąbrowski R., Marzec M., Wróbel S.

Opto-Electronics Review

|

2011

|

Vol. 19, No. 3

270-276

EN

Influence of the electric field upon alignment of molecules in ferro- and antiferroelectric phases has been studied for two fluoro-substituted compounds exhibiting antiferroelectric phase at room temperature. Two different relaxation processes have been revealed in the ferroelectric as well as antiferroelectric phase. Low temperature value of spontaneous polarization is ca. 130 nC/cm² for both substances studied. The substances align very well in the external electric field - a mono-domain of the ferroelectric SmC* phase can be obtained in about 3.5 hours.

2

Electrooptic study of antiferroelectric mixtures for display application

Mikułko A., Marzec M., Wróbel S., Dąbrowski R.

Opto-Electronics Review

|

2006

|

Vol. 14, No. 4

319-322

EN

The aim of this paper is to study the influence of electric field on alignment of para-, ferro- and antiferroelectric phases in the vicinity of SmA* – SmC* or SmC* – SmC*A phase transitions as to obtain mono-domain cells. Four mixtures studied (W-193B, W-193B-1, W-201, W-204D) show the SmC*A phase in a wide room temperature range. Measurements of the spontaneous polarization versus temperature by using reversal current method give an answer to the question, what kind of the transitions take place between para-, ferro- or antiferroelectric phases using the Landau mean field theory. Optimal electrooptic parameters for different compositions of the mixtures such as tilt angle, spontaneous polarization and saturation voltage have been measured to compare parameters of the mixtures studied.

3

Piezoelectric effect and spontaneous polarization in computer modelling of AIII--N heterostructures

Piasecki T., Kośnikowski W., Paszkiewicz B.

Optica Applicata

|

2005

|

Vol. 35, nr 3

597-604

EN

The Ga, Al and In nitrides (AIII--N) are complete material system suitable in high power and high temperature electronic devices such as AlxGa1-xN/GaN heterostructure field effect transistor (HFET). The examples of computer modelling of AIII--N heterostructures were shown. AIII--N materials exhibit strong piezoelectric and spontaneous polarization. The computer modelling results showing the influence of layer polarity on carrier distribution in AlxGa1-xN/GaN heterostructure were shown. Only in Ga-faced heterostructures 2-dimensional electron gas (2DEG) is formed. The effect of AlxGa1-xN layer relaxation on 2DEG concentration in AlxGa1-xN/GaN heterostructure was examined. The difference in spontaneous polarization in AlxGa1-xN and GaN caused high 2DEG concentration even in AlxGa1-xN/GaN heterostructures with relaxed Alx-Ga1-xN layer. Polarization field in AlxGa1-xN layer in AlxGa1-xN/GaN heterostructure was enough for achieving high 2DEG concentrations in undoped heterostructure. Strained AlxGa1-xN layer was introduced into typical HFET heterostructure. GaN layer above an interlayer was depleted and the negative influence of using non semi-insulating GaN layer in HFET transistor was reduced.

4

Electret properties peculiar to fibrous polymer materials

Kravtsov A., Goldade V., Zotov S.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

|

2004

|

Vol. 40, nr 15

9-15

EN

Some peculiar electret properties of fibrous polymer materials have been studied by complementary methods. The residual polarization has been proved to result from capture of free charge carriers on two main types of defects, namely oxygen-containing groups and the defects formed from violated permolecular structure. A spontaneous electrel charge is generated in the fibrous material at both melt blowing and melt spinning and its value depends on the process parameters. The forced polarization of fibers in an external electric field makes the electret effect more pronounced and adds a specific character to the polarizing charge relaxation.

5

Effect of Hydrostatic Pressure on the Low Temperature Phase Transition in Ferroelectrics: (CH3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11

Mróz J.

Polish Journal of Chemistry

|

2003

|

Vol. 77 / nr 4

441-445

EN

Results of hydrostatic pressure on the low temperature ferroelectric-ferroelectric phase transition in (CH3NH3)5Bi2Cl11 at about 170 K and (CH3NH3)5Bi2Br11 at 77 K are presented. The phase transition in both cases revealed a positive pressure coefficient. The pyroelectric coefficients in the vicinity of the low temperature transitions become more and more diffusive as pressure increases.Asimilar molecular mechanism of phase transitions in both methylammonium salts is postulated.