The impact of free charges on the local pressure on a charged ferroelectric domain wall produced by an electric field has been analyzed. A general formula for the local pressure on a charged domain wall is derived considering full or partial compensation of bound polarization charges by free charges. It is shown that the compensation can lead to a very strong reduction of the pressure imposed on the wall from the electric field. In some cases this pressure can be governed by small nonlinear effects. It is concluded that the free charge compensation of bound polarization charges can lead to substantial reduction of the domain wall mobility even in the case when the mobility of free charge carriers is high. This mobility reduction gives rise to an additional imprint mechanism which may play essential role in switching properties of ferroelectric materials. The effect of the pressure reduction on the compensated charged domain walls is illustrated for the case of 180°ferroelectric domain walls and of 90°ferroelectric domain walls with the head-to-head configuration of the spontaneous polarization vectors.
The description and theoretical analysis of a noise shielding system are presented. In this system, the noise and/or sound are transmitted through the piezoelectric curved membrane, which is connected to an external feedback circuit. Using the principle of elasticity control, i.e., utilization of both direct and inverse piezoelectric effects simultaneously, the movement of the membrane as well as the sound pressure of the transmitted wave can be controlled to a large extent. Transmission loss of an audible sound through the membrane in such a system is expressed as a function of a sound frequency, geometrical properties of the membrane, and parameters of the feedback circuit. It is used for the comparison of theoretical predictions and experimental data. Using this technique, the increase of the transmission loss of about 60 dB in a narrow frequency range or about 7 dB in the broad frequency range has been achieved. The performance of this system is discussed.
Macroscopic properties of ferroelectric samples, including those in form of thin films, are, to large extent, influenced by their domain structure. In this paper the free energy is calculated for a plate-like sample composed of nonferroelectric surface layers and ferroelectric central part with antiparallel domains. The sample is provided with electrodes with a defined potential difference.The effect of applied field and its small changes on the resulting domain structure is discussed. This makes it possible to determine the restoring force acting on domain walls which codetermines dielectric and piezoelectric properties of the sample. Calculations of the potential and free energy take into account interactions of opposite surfaces and are applicable also to thin films.
The interaction of electric field with charged domain walls in ferroelectrics is theoretically addressed. A general expression for the force acting per unit area of a charged domain wall carrying free charge is derived. It is shown that, in proper ferroelectrics, the free charge carried by the wall is dependent on the size of the adjacent domains. As a result, the mobility of such domain wall (with respect to the applied field) is sensitive to the parameters of the domain pattern containing this wall. The problem of the force acting on a charged planar 180• domain wall normal to the polarization direction in a periodic domain pattern in a proper ferroelectric is analytically solved in terms of Landau theory. In small applied fields (in the linear regime), the force acting on the wall in such pattern increases with decreasing the wall spacing. It is shown that the domain pattern considered is unstable in a defect-free ferroelectric. The poling of a crystal containing such pattern, stabilized by the pinning pressure, is also considered. Except for a special situation, the presence of charge domain walls makes poling more difficult. The results obtained are also applicable to zigzag walls under the condition that the zigzag amplitude is much smaller than the sizes of the neighboring domains.
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