Volkmar Müller

Influence of the Poling Conditions on the Ferroelectric Properties of Orthorhombic Ba(Ti,Sn)O3 Ceramics

Orthorhombic BaTi 0.95 Sn 0.05 O 3 was poled under varying conditions. Afterwards dielectric, elastic and electromechanical coefficients were derived by analyzing the radial, thickness and length vibration mode. The determined coefficients were used to investigate the influence of the poling parameters, and to understand the structural changes due to the poling. To examine the influence of the microstructure, ceramics with different grain sizes, obtained by changing the sintering temperature, were investigated.

Dynamics of polarization reversal in purified Rb2ZnCl4

Abstract The 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.

MODELING OF DYNAMIC FERROELECTRIC HYSTERESIS LOOPS IN PURIFIED RB2ZNCL4

Dynamic 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.

Elastic properties of purified [N(CH3)4]2CuCl4 crystals near the ferroelastic lock-in transition

Abstract The 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.

Domain wall relaxation in purified Rb2ZnCl4-crystals

Abstract We have studied the frequency dependent domain wall response in the lock-in phase of purified RZC crystals. Our investigations carried out at low measuring fields reveal for the first time a pronounced temperature hysteresis of the relaxation time τ in the interval 193 K > T > 170 K and a steep increase of τ on cooling below T = 165 K.

Polarization reversal and dielectric slowing down in the lock-in phase of Rb2ZnCnl4

Abstract Data are presented on polarization reversal and on permittivity measured during switching in the lock in phase of purified Rb2ZnCl4 crystals. Hysteresis loops have the characteristic “swan neck” shape close below Tc but change to conventional form at lower temperatures. The coercive field is not a true threshold field; for slow switching it is as low as tens of V/cm. The value of permittivity and its relaxation frequency are strongly influenced by the domain configuration during polarization reversal. The relaxation frequency is of the order of 102 to 103 Hz, reaches a minimum around Ec and decreases with decreasing temperature.

Nonlinear dielectric properties of CsH2PO4

Abstract The temperature dependence of the fourth order dielectric coefficient e2222 of CsH2PO4 was determined above the ferroelectric transition temperature Tc. The critical behaviour of this coefficient differs from those of proper uniaxial ferroelectrics and can be described using a pseudo- one-dimensional Ising model. Below Tc the sample capacitance is in the range of small driving voltages strong voltage dependent.

Elastic, electromechanical and dielectric properties of CsH2 PO4

Abstract The elastic compliances sE11 /sE33 and the electromechanical coefficients Q221 /Q223 have been measured for CsH2PO4 in a great temperature range above the ferroelectric phase transition. The temperature dependence of these coefficients as well as those of the dielectric constant can be well explained in terms of the quasi-one-dimensional Ising model developed by Carvalho and Salinas, extended to compressible cases.

Electromechanical resonance study of phase transition of quasi-one-dimensional ferro-electrics CsH2PO4

Abstract The influence of an electric bias field E2 on elastic compliance s33 and dielectric permittivity e22 of CsH2PO4 has been studied in a temperature region including ferroelectric transition point. Shape and value of anomaly of s33 are strongly influenced by E2 and temperature of s33 maximum is displaced to lower values.

Nonlinear dynamics of a series resonance circuit containing purified Rb2ZnCl4

Abstract The nonlinear dynamics of a series resonance circuit containing purified Rb2ZnCl4 shows period doubling cascades and chaotic behaviour and displays poling and ageing processes of the ferroelectric domain structure.