Browsing by Author "Müller, Volkmar"
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- ItemDynamics of polarization reversal in purified Rb2ZnCl4(1997) Hauke, Tilo; Müller, Volkmar; Beige, Horst; Fousek, JanThe dynamics of polarization reversal in sinusoidal fields (0. 1Hz≤f≤50kHz) was studied in the ferroelectric lock-in phase of purified Rb2ZnCl4 crystals. The frequency dependence of remanent polarization and coercive field Ec is qualitatively the same above and below T*≈160K, where for all measuring frequencies Ec starts to increase rapidly with decreasing temperature. A model which treats sideways shifts of planar, nearly regularly arranged domain walls as the only mechanism of polarization reversal in Rb2ZnCl4 is applicable for the quantitative description of ferroelectric hysteresis loops in the whole temperature interval under investigation. The anomalous increase of Ec at T* seems to be connected to a corresponding increase of the viscosity coefficient.
- ItemElastic properties of purified [N(CH3)4]2CuCl4 crystals near the ferroelastic lock-in transition(1996) Müller, Volkmar; Fuith, Armin H.; Fousek, Jan; Warhanek, Hans; Beige, HorstThe low frequency elastic properties of ferroelastic [N(CH3)4]2CuCl4 crystals are investigated by dynamical mechanical analysis in the vicinity of the incommensurate-commensurate phase transition. We show for the first time, that the anomaly of the elastic compliance coefficient S55, even of purified crystals, is accompanied by typical nonequilibrium phenomena such as isothermal relaxations. The S55(T) anomaly was not significantly enhanced by the purification treatment. We conclude, that extended defects induced during crystal growth have a decisive influence on the elastic properties of [N(CH3)4]2CuCl4.
- ItemModeling of dynamic ferroelectric hysteresis loops in purified Rb2ZnCl4(1996) Hauke, Tilo; Müller, Volkmar; Beige, Horst; Fousek, JanDynamic hysteresis loops were recorded in the ferroelectric lock-in phase of purified Rb2ZnCl4 crystals at a temperature T=188 K which is 5 K below the incommensurate-commensurate phase transition. The hysteresis loops observed in the frequency range 50 Hz<f<5 kHz can quantitatively be described by a model that treats a sideways shift of planar, nearly regular arranged domain walls as the only mechanism of polarization reversal in Rb2ZnCl4. Due to defect interaction, the velocity v of the domain wall depends nonlinearly on the effective force F acting on it and a scaling behavior v∼(F-Fc)θ with θ=1.45 is observed. © 1996 American Institute of Physics.
- ItemSpontaneous strain in ferroelastic incommensurate [N(CH3)4]2CuCl4 crystals(1997) Müller, Volkmar; Fuith, Armin H.; Fousek, Jan; Warhanek, Hans; Beige, HorstThe temperature dependence of spontaneous strain is investigated in the ferroelastic lock-in phase of [N(CHs),&CuCIi crystals by thermal mechanical analysis. The critical index of the order parameter modulus is found to be j3 =0.33. Considerable wall displacements have been detected for shear stress as small as a, =2.4kPa which indicates that the mechanical pinning energy is extremely small. 0 1997 Published by Elsevier Science Ltd