Domain size and charge defects affecting the polarization switching of antiferroelectric domains

The switching behavior of antiferroelectric domain structures under the applied electric field is not fully understood.In this work,by using the phase field simulation,we have studied the polarization switching property of antiferroelectric domains.Our results indicate that the ferroelectric domains nucleate preferably at the boundaries of the antiferroelectric domains,and antiferroelectrics with larger initial domain sizes possess a higher coercive electric field as demonstrated by hysteresis loops.Moreover,we introduce charge defects into the sample and numerically investigate their influence.It is also shown that charge defects can induce local ferroelectric domains,which could suppress the saturation polarization and narrow the enclosed area of the hysteresis loop.Our results give insights into understanding the antiferroelectric phase transformation and optimizing the energy storage property in experiments.

Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO_(2) Thin Films

Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.

Semi-quantitative study on the Staebler-Wronski effect of hydrogenated amorphous silicon films prepared with HW-ECR-CVD system

The method of numerical simulation is used to fit the relationship between the photoconductivity in films and the illumination time. The generation and process rule of kinds of different charged defect states during illumination are revealed. It is found surprisingly that the initial photoconductivity determines directly the total account of photoconductivity degradation of sample.

Free charge localization and effective dielectric permittivity in oxides

This review will deal with several types of free charge localization in oxides and their consequences on the effective dielectric spectra of such materials.The first one is the polaronic localization at the unit cell scale on residual impurities in ferroelectric networks.The second one is the collective localization of free charge at macroscopic interfaces like surfaces,electrodes and grain boundaries in ceramics.Polarons have been observed in many oxide perovskites mostly when cations having several stable electronic configurations are present.In manganites,the density of such polarons is so high as to drive a net lattice of interacting polarons.On the other hand,in ferroelectric materials like BaTiO_(3)and LiNbO_(3),the density of polarons is usually very small but they can influence strongly the macroscopic conductivity.The contribution of such polarons to the dielectric spectra of ferroelectric materials is described.Even residual impurities as for example Iron can induce well-defined anomalies at very low temperatures.This is mostly resulting from the interaction between localized polarons and the highly polarizable ferroelectric network in which they are embedded.The case of such residual polarons in SrTiO_(3)will be described in more detail,emphasizing the quantum polaron state at liquid helium temperatures.Recently,several nonferroelectric oxides have been shown to display giant effective dielectric permittivity.It is first shown that the frequency/temperature behavior of such parameters is very similar in very different compounds(donor-doped BaTiO_(3),CaCu_(3)Ti_(4)O_(12),LuFe_(2)O_(4),Li-doped NiO,etc.).This similarity calls for a common origin of the giant dielectric permittivity in these compounds.A space charge localization at macroscopic interfaces can be the key for such extremely high dielectric permittivity.