TY  - JOUR
A1  - Frübing, Peter
A1  - Wegener, Michael
A1  - Gerhard, Reimund
A1  - Buchsteiner, Alexandra
A1  - Neumann, Werner
A1  - Brehmer, Ludwig
T1  - Different molecular mechanisms for the dielectric hysteresis and pyroelectricity in a poly(vinyl alcohol) with azobenzene-alkoxy side chains
N2  - By means of pyroelectrical measurements and dielectric spectroscopy as well as structural information from differential scanning calorimetry, it is shown that, in a poly(vinyl alcohol) with azobenzene-alkoxy side chains, pyroelctricity and dielectric hysteresis which are usually related to each other have different origins. The pyroelectric effect is explained with reversible dipole-density changes upon thermal expansion, whereas the dielectric hysteresis is proposed to result from a charge-carrier polarisation.
Y1  - 1999
SN  - 0277-786X
ER  - 
TY  - JOUR
A1  - Frübing, Peter
A1  - Wegener, Michael
A1  - Gerhard, Reimund
A1  - Buchsteiner, Alexandra
A1  - Neumann, Werner
A1  - Brehmer, Ludwig
A1  - Dietel, Reinhard
T1  - Pyroelectric properties and dielectric hysteresis of a poly(vinylalcohol) with azobenzene alkoxy side chains
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Neumann, Werner
A1  - Buchsteiner, Alexandra
A1  - Mahler, Willy
A1  - Geue, Thomas
A1  - Pietsch, Ullrich
T1  - Dielectric loss spectroscopy at fatty acid salt multilayers
N2  - Dielectric loss spectroscopy (DLS) was performed at compact samples and lamellary organized Langmuir-Blodgett (LB) films from various fatty acid salts. Previous thermoanalytical measurements at compact samples revealed the appearance of two different phase transition temperatures; the lower one is related to the acid the second one to the acid salt molecules. In spite of ill defined electrical contacts with the film the characteristic DLS frequencies obtained from about 100nm thick multilayer films are similar to those recorded from bulk samples. No significant variations of frequencies were found changing the counter ions. Besides conductivity influence at low frequncies we found two relaxations related to the mobility of the dipolar carboxylat-metal group at about 100 and 10000Hz. One of these frequencies is related to the rotation around the chain axis. The strength of this relaxation increases significantly with increasing the sample temperature above 105°C. This temperature is connected with a structural phase transition observed by X-ray reflectometry. In case of Pb-stearate the results of the dielectric measurements help to interprete this structural change as a transition from an orthorhombic into a free-rotator phase. The uncorrelated rotation of molecules around their molecular axes initiates a much increased relaxation strength at the carboxylat-metal sites.
Y1  - 2000
ER  -