Asymmetric hysteresis loops and smearing of the dielectric anomaly at the transition temperature due to space charges in ferroelectric thin films

Abstract

Ferroelectric thin films often exhibit a displacement of the polarization versus the electric field hysteresis loops, particularly along the electric field axis. This shift is typically attributed to structural and electronic asymmetry of the film-electrode interfaces, asymmetric surface fields, as well as space charge regions. In this study, we analyze the effect of a spatial, continuous distribution of space charge on the hysteresis response and phase transition characteristics of epitaxial ͑001͒ PbZr 0.3 Ti 0.7 O 3 thin films sandwiched between metallic electrodes on ͑001͒ SrTiO 3 substrate. Using a nonlinear thermodynamic model, we compute numerically the internal electrical fields and polarizations for several different space charge distributions both in the presence of a triangular external electric field and as a function of temperature at zero applied field. We show that space charge accumulated near the metal-ferroelectric interfaces can dramatically displace the hysteresis along the electric field axis such that the otherwise symmetric coercive fields E C − and E C + in a bulk ferroelectric related to each other through ͉E C −͉ = E C + may shift depending on the space charge concentration in such a manner that both E C − , E C + Ͼ 0 or E C − , E C + Ͻ 0. This gives rise to a very strong imprint. Our findings reveal that the presence of space charges in ferroelectric thin films results in significant changes in the phase transition characteristics, including a reduction in the phase transition temperature, smearing of the transition over a temperature range instead of a sharp dielectric anomaly at the bulk Curie temperature, and a reduction in the dielectric response compared to defect-free ferroelectrics of the same composition.

Intrinsic anomalous ferroelectricity in vertically aligned LiNbO3-type ZnSnO3 hybrid nanoparticle-nanowire arrays

“…12 Anomalous behaviors in FE hysteresis loops, such as constriction or pinching at low fields, [13][14][15][16] and/or asymmetric E c and P r values are often encountered in FE thin films and nanostructures. [17][18][19] These may result from space charge effects, 20 such as charged defects, trapped charges (oxygen vacancies), and other possible defect-dipole complexes (vacancyacceptor dipoles) created during the growth of the FE structures, 12 or with aging. 21 The presence of the charged defects and defect-dipoles may create a pinning-effect on the domain wall motion which also can distort the symmetric hysteresis shape.…”

“…16,17,20,37,38 In this respect, the Preisach theory of hysteresis, originally proposed to describe the interactions of ferromagnetic nanoparticles was extended to the realm of FE materials. 39,40 Using the Preisach approach, the constricted hysteresis loop can be simulated by considering a symmetric distribution of switchable bistable units (such as defect dipoles) in a FE material.…”

A new method for achieving enhanced dielectric response over a wide temperature range

“…While extremely high-quality ceramic multilayers can be produced as shown in this study, it is difficult to compare the properties of interlayer interfaces in such samples to “perfect” heteroepitaxial, ultra-thin heterostructures32. Considering the mixed ionic and covalent interatomic bonding in perovskite ferroelectrics, their susceptibility to the formation of oxygen vacancies, and the presence of other structural defects such as impurities, dislocations, grain boundaries which have stress fields that generate commensurate polarization variations, the coupling between interlayers becomes extremely complex33. Taking into account that the interfaces in bulk ceramic samples are less than perfect ( κ  ≈ 1—no space charges), we take κ  = 10 −4 for configuration of Fig.…”

The effects of grain size on electrical properties and domain structure of BiFeO3 thin films by sol–gel method

“…6a), which indicates that the slight difference of work function between top and bottom electrodes (Au: 5.1 eV, Pt: 5.65 eV) in our case may not the main reason. Second, the internal field is built through the imprint process caused by defect [50]. As mentioned above, oxygen vacancy forms easily during the preparation of BFO thin films because of the reduction of Bi V ÁÁ o ) located in the grain boundary and the film-electrode interface can promote a local stoichiometry deviation influencing the shape of the P-E hysteresis loops.…”