Effects Of Interface On Ferroelectric Properties Of Film With Charged Domain Walls: A Phase Field Simulation

Domain structure and domain moving under the external field are closely related toproperties such as piezoelectric, ferroelectric properties of ferroelectric thin films. Sothe study of influence of domain switching on the properties of ferroelectric thin filmhas a great significance to understand mechanism of properties and to regulate theproperties of ferroelectric thin films. Several recent works have drawn attention toso-called charged domain walls, and the results show that the charged domain wallshave great influence on the piezoelectric properties. Therefore, it is very important todevelop a model to analyze moving of charged domain walls under the external fieldand which effecting on the properties of ferroelectric thin films. In addition, theinterface has a great influence on the properties of ferroelectric thin films. So it isnecessary to develop a model to analyze the influence of interface on the domain andproperties of ferroelectric thin films. In this paper we develop a phase field model forthe ferroelectric thin films with charged domain walls, and investigate the effects ofthe applied electric field, the misfit strain and the charge density in the chargeddomain walls on the ferroelectric properties of the film films. Meanwhile, theinfluence of interface on the domain structures and properties of ferroelectric thinfilms has been study. The main contents and conclusions of this paper are summarizedas follows:A phase field model of the ferroelectric thin films with charged domain walls isdeveloped and the switching of charged domain walls in applied electric field hasbeen investigated. The results suggest that the model of charged domain wallsswitching is related to the direction of the applied electric field. When there is thepositive x-axis direction applied electric field, charged domain walls switch fromhead-to-head (HH) and tail-to-tail (TT) domain walls to head-to-tail domain wallsfirstly, then switch to head-to-head (HH) and tail-to-tail (TT) domain walls, andswitch to single-domain finally, different form the process of charged domain wallswitching when the direction of applied electric field is the negative x-axis direction,which is that head-to-head (HH) and tail-to-tail (TT) domain walls switch tosingle-domain direct.The ferroelectric properties of the thin films with charged domain walls have beenconsidered used by phase field model. The results show that the hysteresis loop scalesdown as decreases of the frequency of the applied electric. The hysteresis loop of the ferroelectric thin films with charged domain walls is asymmetric, and has a higherfrequency-dependence than which of the thin films with uncharged domain walls. Thecoercive field, remnant polarization is less than which of thin films with unchargeddomain walls. Meanwhile, frequency-dependence increases with the charge density inthe charged domain wall.An improved phase field model considering the effect of interface is developed.The interface electric field and interface strain has been considered in the ferroelectricproperties the thin films with charged domain walls. The results show that thesymmetrical interface electric field lead to the appearance of uncharged domain wallsand charged domain walls in thin films which with charged domain walls in the initialmoment. The coercive field, saturation polarization, residual polarization decreaseswith the increase of the symmetrical interface electric field. The asymmetric interfaceelectric field lead to hysteresis loop deviation increasingly with the increase of theelectric field. The influence of actual misfit strain on the ferroelectric properties of thethin film rapidly decreases with the increase of the thickness of thin film. When thethickness exceeds40nm, the effect of actual misfit strain on the properties is weak.