Polarization Switching without Domain Formation at the Intrinsic Coercive Field in Ultrathin Ferroelectric PbTiO 3
ABSTRACT Polarization switching in ferroelectrics has been thought to occur only through the nucleation and growth of new domains. Here we use in situ synchrotron x-ray scattering to monitor switching controlled by applied chemical potential. In sufficiently thin PbTiO₃ films, nucleation is suppressed and switching occurs by a continuous mechanism, i.e., by uniform decrease and inversion of the polarization without domain formation. The observed lattice parameter shows that the electric field in the film during switching reaches the theoretical intrinsic coercive field.
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ABSTRACT: Thermodynamic theory is developed for the ferroelectric phase transition of an ultrathin film in equilibrium with a chemical environment that supplies ionic species to compensate its surface. Equations of state and free energy expressions are developed based on Landau-Ginzburg-Devonshire theory, using electrochemical equilibria to provide ionic compensation boundary conditions. Calculations are presented for a monodomain PbTiO$_3$ (001) film coherently strained to SrTiO$_3$ with its exposed surface and its electronically conducting bottom electrode in equilibrium with a controlled oxygen partial pressure. The stability and metastability boundaries of phases of different polarization are determined as a function of temperature, oxygen partial pressure, and film thickness. Phase diagrams showing polarization and internal electric field are presented. At temperatures below a thickness-dependent Curie point, high or low oxygen partial pressure stabilizes positive or negative polarization, respectively. Results are compared to the standard cases of electronic compensation controlled by either an applied voltage or charge across two electrodes. Ionic surface compensation through chemical equilibrium with an environment introduces new features into the phase diagram. In ultrathin films, a stable non-polar phase can occur between the positive and negative polar phases when varying the external chemical potential at fixed temperature, under conditions where charged surface species are not present in sufficient concentration to stabilize a polar phase.Physical review. B, Condensed matter 12/2010; 84(6). DOI:10.1103/PhysRevB.84.064107 · 3.66 Impact Factor
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ABSTRACT: Recent developments in ferroelectric (FE) domain imaging techniques have established an understanding of intriguing polarization switching dynamics. In particular, nanoscale studies of FE domain switching phenomena using piezoresponse force microscopy (PFM) can provide important microscopic details on nucleation and subsequent growth of domains, complementing conventional electrical measurements that only give macroscopic information. This review covers recent nanoscale PFM studies of domain switching dynamics in FE thin films. Recent nanoscale PFM-based studies have demonstrated that quenched defects inside the FE thin films play important roles in domain switching processes, including defect-mediated inhomogeneous nucleation, pinning-dominated nonlinear dynamics of domain walls, and many other intriguing phenomena.Highlights►We review recent piezoresponse force microscopy studies of ferroelectric domains. ►Piezoresponse force microscopy has provided nanoscale details of domain switching. ►Quenched defects in ferroelectric thin films act as nucleation centers. ►Defects also act as pinning sites for propagating ferroelectric domain walls.Current Applied Physics 09/2011; 11(5):1111-1125. DOI:10.1016/j.cap.2011.05.017 · 2.03 Impact Factor
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ABSTRACT: Evolutions of domain morphology in the ferroelectric thin film subjected to the oxidizing atmosphere were predicted by using the phase field simulations, which incorporate the long-range electrostatic interactions and ionic surface charges. Due to effect of the oxidizing atmosphere, it is found that the ionic surface charges carried by oxygen can effectively change the internal electric filed, control the polarization orientation, and drive the domain wall motion of the ferroelectric thin film. Domain structures were simulated and also reveal that domain morphology of the ferroelectric thin film can be adjusted from a multi-domain to a mono-domain with increasing of the ionic charge density. (C) 2011 American Institute of Physics. [doi:10.1063/1.3646387]Applied Physics Letters 10/2011; 99(110):142908-52004. DOI:10.1063/1.3646387 · 3.52 Impact Factor