Berlin 2012 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 3: Nonlinear dielectrics, phase transitions, relaxors

DF 3.3: Vortrag

Montag, 26. März 2012, 15:40–16:00, EB 107

Investigation of the ferroelectric phase transition at silver sodium nitrite using noise measurements — •Jumna Mehlis, Ulrich Straube, and Martin Diestelhorst — Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle

The thermal current noise in the vicinity of the ferroelectric-paraelectric phase transition was studied. For this purpose silver sodium nitrite is well-suited, because of its low relaxation frequencies. The current noise density of a short-circuited single crystal was amplified by a low noise operational amplifier. The noise spectra were measured as a function of the temperature by using a spectrum analyzer. The results are in agreement to the Nyquist theorem. That means the noise density is proportional to the temperature and the losses. Contrary to ohmic resistors the thermal noise density of ferroelectrics depends on the frequency. Moreover, the measured spectra show a characteristical change of the shape in dependence on the temperature. This change is strongly correlated with the ferroelectric phase transition temperature, which was determined by the simultaneously measured dielectric function.