Polarization Of BaTiO3 Research Articles

Mathematical model of electrical and mechanical yielding for piezoelectric strip weakened by a non-centric semi-permeable crack

A mathematical strip-electro-elastic yielding model solution is obtained for a long and narrow piezoelectric strip weakened by a non-centric, semi-permeable, mode-III crack. The crack is oriented parallel and situated asymmetrically with respect to the edges of the strip. Fourier cosine integral transform technique is adopted to solve the problem. Three different cases are considered: when developed saturation zone is bigger, smaller or equal to the developed slide-yield zone. Closed-form analytic expressions are derived for developed zones lengths, crack sliding displacement, crack opening potential drop, field intensity factors and energy release rate. A numerical case study is presented for poled BaTiO3 piezoelectric ceramic which affirms that proposed model is capable of crack arrest under small-scale mechanical and electrical yielding.

An ultra-broad working temperature dielectric material obtained with Praseodymium doped BaTiO3–(Bi0.5Na0.5)TiO3–Nb2O5 based ceramics

A material with stable permittivity (the capacitance is within ±15% of room temperature capacitance) at an ultra-broad temperature range of −55–300°C has been achieved by doping appropriate amount (mol%) of Pr6O11 in multicomponent BaTiO3–(Bi0.5Na0.5)TiO3–Nb2O5 based ceramics. A remarkable high ceiling working temperature of 300°C has been achieved by the doping of Pr6O11. It played a crucial role in the stability of high-temperature dielectric properties. While increasing the doping content of Pr6O11, the dielectric constant was decreased significantly at the temperature range of 200–300°C and the maximum TCC value was reduced from 39% to only 4%. XRD results showed the substitution of Pr ion appeared in both Ba-site and Ti-site. The substitution decreased the spontaneous polarization of BaTiO3 and then weakened the ferroelectricity of BaTiO3. As a result, the temperature stability of samples was improved obviously. Besides, Pr6O11 addition promoted the formation of sheet grains, which were consisting of BaTi4O9. The best dielectric and electrical properties (εr=1608, tanδ=1.54%, ρV=2.15×1012Ωcm) at room temperature appear in the sample with 0.6mol% Pr6O11 addition.

On the superparamagnetic size limit of nanoparticles on a ferroelectric substrate

When decreasing the size of nanoscale magnetic particles, their magnetization becomes vulnerable to thermal fluctuations as the superparamagnetic limit approaches, thus hindering applications relying on a stable magnetization. Here, we theoretically investigate how a magnetoelectric coupling to a ferroelectric substrate modifies the superparamagnetic limit, with a special focus on the possible realization of substantially smaller multiferroic clusters with thermally stable magnetization. For an estimate of cluster size we perform calculations for iron nanoparticles multiferroically coupled to a BaTiO3 substrate. Our numerical results indicate that steering the polarization of BaTiO3 with electric fields affects the magnetism of the deposited magnetic clusters. The work provides a suggestion on how the strength of the magnetoelectric coupling might be extracted from telegraph noise experiments.

Field-effect BaTiO3-Si solar cells

Conventional solar cells make use of the spatial variation in electronic environment due to junctions for charge separation. We investigated field-effect BaTiO3-Si solar cells that utilize the bound surface charges of BaTiO3 to separate charge carriers in silicon. Rectifying behavior and photovoltaic effect were observed on cells with forward polarization. Theoretical simulation indicated that the induced electric field due to BaTiO3 polarization could extend into the silicon layer, which is consistent with experimental observations. In addition, adjusting relevant parameters may optimize the electric field distribution. The cells are promising in terms of material selection, device design, and fabrication.

Electric control of magnetism at the Fe/BaTiO3 interface

Interfacial magnetoelectric coupling is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO3 system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BaTiO3 dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichroism in combination with high resolution electron microscopy and first principles calculations, we report on an undisclosed physical mechanism for interfacial magnetoelectric coupling in the Fe/BaTiO3 system. At this interface, an ultrathin oxidized iron layer exists, whose magnetization can be electrically and reversibly switched on-off at room-temperature by reversing the BaTiO3 polarization. The suppression / recovery of interfacial ferromagnetism results from the asymmetric effect that ionic displacements in BaTiO3 produces on the exchange coupling constants in the interfacial oxidized Fe layer. The observed giant magnetoelectric response holds potential for optimizing interfacial magnetoelectric coupling in view of efficient, low-power spintronic devices.

Magnetic properties and electronic structures of (YTiO3)2/(BaTiO3)n superlattices

The magnetic properties and electronic structures of (YTiO3)2/(BaTiO3)n superlattices are investigated using the first-principles calculations. It is revealed that the in-plane compressive strain results in the A-type antiferromagnetic order in the YTiO3 component. Surprisingly, the Ti ions in BaTiO3 layers exhibit a weak ferromagnetic order for n = 4. The ferromagnetism in the BaTiO3 layers near the interface is related to the polar discontinuity of YTiO3 and ferroelectric polarization of BaTiO3. The electronic structures indicate that the n = 4 superlattice shows the two-dimensional electron gas at the interface.

Ultra‐Broad Temperature Stability Obtained with Ce‐Doped BaTiO3‐Based Ceramics

Ce‐doped BaTiO3‐based ceramics were prepared and studied to satisfy ultra‐broad temperature stability (from −55°C to 300°C, capacitance variation rate based on C20°C is within ±15%). The sample with 0.6 mol% CeO2 succeeds to achieve this performance with a remarkably high ceiling temperature of 300°C. Meanwhile, the sample has good dielectric and electrical properties at room temperature (εr = 1667, tanδ = 1.478%, ρV = 5.9 × 1012 Ω·cm). Ce ion can substitute for Ti ion as Ce4+ or Ba ion as Ce3+. The substitution decreases the spontaneous polarization of BaTiO3, and then weakens the ferroelectricity of BaTiO3. As a result, the temperature stability of samples is improved obviously. Besides, CeO2 addition promotes the formation of exaggerated grains, which are consisting of Ba6Ti17O40.

Ultrahigh actuation strains in BaTiO3 and Pb(Mn1/3Nb2/3)O3-PbTiO3 single crystals via reversible electromechanical domain switching

Non-180° domain-switching induced strains in ferroelectrics, although much larger than piezoelectric strains, had been thought unusable as they are usually irreversible. Here, we show that under a uni-polar field of 800 V/mm with a prestress which depoles the material nearly completely, a reversible strain of 0.93% can be realized in a poled BaTiO3 crystal. Similarly, we realized an actuation strain of 0.66% in a tetragonal 0.62Pb(Mn1/3Nb2/3)O3-0.38PbTiO3 crystal at 1.8 kV/mm. The obtained large actuation strains are caused by reversible 90° domain-switching under electromechanical loading. Furthermore, the large strains are quite stable and have quick responses, very promising for practical actuator applications.

Lattice screening of the polar catastrophe and hidden in-plane polarization in KNbO3/BaTiO3interfaces

We have carried out first-principles simulations, based on density functional theory, to obtain the atomic and electronic structure of (001) BaTiO$_{3}$/KNbO$_{3}$ interfaces in an isolated slab geometry. We tried different types of structures including symmetric and asymmetric configurations, and variations in the thickness of the constituent materials. The spontaneous polarization of the layer-by-layer non neutral material (KNbO$_{3}$) in these interfaces cancels out almost exactly the "built-in" polarization responsible for the electronic reconstruction. As a consequence, the so-called polar catastrophe is quenched and all the simulated interfaces are insulating. A model, based on the modern theory of polarization and basic electrostatics, allows an estimation of the critical thickness for the formation of the two-dimensional electron gas between 42 and 44 KNbO$_{3}$ unit cells. We also demonstrate the presence of an unexpected in-plane polarization in BaTiO$_{3}$ localized at the $p$-type TiO$_2$/KO interface, even under in-plane compressive strains. We expect this in-plane polarization to remain hidden due to angular averaging during quantum fluctuations unless the symmetry is broken with small electric fields.

Grain-size effects on dielectric and piezoelectric properties of poled BaTiO3 ceramics

Barium titanate (BaTiO3) is known historically as the first ceramic piezoelectric material and shows a high possibility of being revitalized as a popular lead-free piezoelectric material. However, few systematic studies of the grain-size effects on the dielectric and piezoelectric properties of poled BaTiO3 ceramics have been carried out to date. In this work, a series of dense BaTiO3 ceramics with uniform grain-size distribution were successfully prepared by the conventional solid-state reaction, and the grain-size effects on the dielectric and piezoelectric properties were explored in their poled states. An interesting physical phenomenon has been found: dielectric permittivity ε′ and the piezoelectric constant d33 increase significantly at room temperature with the reduction of the average grain size g and reach the maxima at g=0.94μm. It was revealed that domain structure and relative density play substantial roles in determining the ε′ and d33 behaviors. The average 90° domain width decreases monotonically with g. Both the 90° domain wall density and the area dimension of area dimension domain wall are considered as important factors that greatly influence the d33 value. Extrinsic contribution comprises the major part of the observed d33 values in the fine-grained BaTiO3 ceramics.

Ferroelectric control of the magnetocrystalline anisotropy of the Fe/BaTiO3(001) interface

Density-functional calculations are employed to investigate the effect of ferroelectric polarization of BaTiO3 on the magnetocrystalline anisotropy of the Fe /BaTiO3(001) interface. It is found that the interface magnetocrystalline anisotropy energy changes from 1.33 to 1.02 erg cm −2 when the ferroelectric polarization is reversed. This strong magnetoelectric coupling is explained in terms of the changing population of the Fe 3d orbitals at the Fe/BaTiO3 interface driven by polarization reversal. Our results indicate that the electronically assisted magnetoelectric effects at the ferromagnetic/ferroelectric interfaces may be a viable alternative to the strain mediated coupling in related heterostructures and the electric field-induced effects on the interface magnetic anisotropy in ferromagnet/dielectric structures.

A temperature-dependent study on the polarization-free straining of barium titanate singlecrystals

Previous studies by the authors have shown that, when subjected to combined uniaxialstress and electric field at room temperature, a (001)-oriented barium titanate (BaTiO3) single crystal may display incomplete switching characteristics and a severe disproportionof slope gradients at zero electric field for its polarization and strain hysteresis curves. It isproposed that the likely causes for the observed ‘decoupling’ of switching strain andswitching polarization at room temperature are the cooperative operation of multiple90° switching systems, by which ‘polarization-free’ strain changes could be induced, and the presenceof depolarization fields generated from the unshielded boundaries and/or incompatible domainswithin the crystal. In the present study, the evolution of polarization and strain hystereses ofBaTiO3 single crystals under various electromechanical loading combinations are investigated again at55 °C. When compared to the hysteresis measurements at room temperature,the degree of discrepancy between the slope gradients at zero electricfield for the polarization and strain hysteresis curves measured at55 °C is significantly reduced. This is due to the increase in domain wall mobility at a highertemperature, lowering the extent of incomplete switching at maximum electric field. At55 °C, domainswith 180° relative orientation are less likely to exist at maximum electric field; hence, the criticalprerequisite for polarization-free straining is no longer available. The experimental dataobtained in the present study are expected to assist the development of reliable constitutivemodels for single-crystal ferroelectrics.

Strain-coupled ferroelectric polarization in BaTiO3–CaTiO3 superlattices

We report on growth and ferroelectric (FE) properties of superlattices (SLs) composed of the FE BaTiO3 and the paraelectric CaTiO3. Previous theories have predicted that the polarization in (BaTiO3)n/(CaTiO3)n SLs increases as the sublayer thickness (n) increases when the same strain state is maintained. However, our BaTiO3/CaTiO3 SLs show a varying lattice-strain state and systematic reduction in polarization with increasing n while coherently strained SLs with n=1 and 2 show a FE polarization of ca. 8.5 μC/cm2. We suggest that the strain coupling plays a more important role in FE properties than the electrostatic interlayer coupling based on constant dielectric permittivities.

Spherical nanoindentation and Vickers microhardness study of the deformation of poled BaTiO3 single crystals

In this work, Vickers microhardness and spherical nanoindentation (NI) experiments—with hemispherical radii, R, of 13.5, 5, and 1.4μm—were used to explore the room temperature deformation behavior of poled barium titanate (BaTiO3) single crystals with two orientations: (001) and (110). At 209±11 and 193±11GPa, Young’s moduli of the (001) and (110) surfaces, respectively, were comparable. The (001) surface deforms elastically, before a pop-in event, followed by a strain-hardening regime. The pop-in stresses are stochastic in nature and can be described by Weibull statistics. The (110) surface deforms elastically, then plastically at lower stresses, before cracks are initiated, beyond which the strain-hardening regime is almost identical to that of the (001) surface. This three-regime behavior of the (110) surface was confirmed by postindentation scanning electron microscope micrographs. This work confirms that the room temperature deformation of single crystal BaTiO3 occurs by glide on the {110} slip planes that are also the cleavage planes. Furthermore fully reversible reproducible stress/strain loops were observed and attributed to the formation and annihilation of fully reversible dislocation loops, whose threshold stresses were a function of the domain size that forms under the various indenters. The domain sizes appear to scale with R and are believed to be responsible for the NI size effect observed.

Surface and Interface Effects on the Dielectric Polarization and Refractive Indices of BaTiO3 Ultrathin Films

The surface effect on the dielectric polarization and refractive indices of BaTiO 3 ultrathin films on SrTiO 3 single crystal substrates is investigated theoretically by using a microscopic model based on the orbital approximation in correlation with the dipole–dipole interaction. The spontaneous polarization of the BaTiO 3 /SrTiO 3 film is reduced as its thickness decreases. However, an electronic polarization appears within the SrTiO 3 substrate in the neighborhood of the interface. This polarization, which vanishes far away from the interface into the SrTiO 3 bulk, is induced by the polarization of the BaTiO 3 film. Furthermore, we find the refractive index either for BaTiO 3 films or for SrTiO 3 substrates to be strongly reduced for light polarized perpendicular to the surface.

High piezoelectric properties and domain configuration in BaTiO3 ceramics obtained through the solid-state reaction route

BaTiO3 ceramics with a high piezoelectric coefficient have been successfully obtained through the conventional solid-state reaction route starting from ordinary BaCO3 and TiO2 powders. The ceramics sintered at 1210 °C exhibit excellent piezoelectric properties of d33 = 419 pC N−1 and kp = 0.453 with tan δ = 1.36% at room temperature. The crystallographic structure, the microstructure and the domain pattern were investigated. It has been revealed that d33 increases and the average domain width in the poled BaTiO3 ceramics remains approximately constant at around 240 nm with the decrease in the average grain size from 9.5 to 2.0 µm. From the analysis, we suggest that the largeness of the domain wall is an important factor, which significantly influences the piezoelectric properties.

Tailoring magnetic anisotropy at the ferromagnetic/ferroelectric interface

It is predicted that magnetic anisotropy of a thin magnetic film may be affected by the polarization of a ferroelectric material. Using a Fe∕BaTiO3 bilayer as a representative model and performing first-principles calculations, we demonstrate that a reversal of the electric polarization of BaTiO3 produces a sizable change in magnetic anisotropy energy of Fe films. Tailoring the magnetic anisotropy of a nanomagnet by an adjacent ferroelectric material may yield entirely new device concepts, such as electric-field controlled magnetic data storage.

Effects of ferroelectricity and magnetism on electron and spin transport in Fe∕BaTiO3∕Fe multiferroic tunnel junctions

First principles electronic structure and transport calculations are used to demonstrate the impact of the electric polarization on electron and spin transport in Fe∕BaTiO3∕Fe multiferroic tunnel junctions (MFTJs). We find that the polarization of BaTiO3 reduces the tunneling conductance, as compared to a nonpolarized barrier, due to the change in the electronic structure driven by ferroelectric displacements, similar to that found previously for Pt∕BaTiO3∕Pt. For the MFTJ, however, this effect has different magnitudes for majority- and minority-spin channels and for parallel and antiparallel orientations of the magnetization of the electrodes. As a result, we find a substantial drop in the spin polarization of the tunneling current in the parallel configuration and an inversion of the magnetoresistance as polarization of the barrier is turned on.

Effects of lattice strain and ion displacement on the bonding mechanism of the ferroelectric perovskitematerial BaTiO3: first-principles study

The effects of lattice strain and ion displacement on the bonding mechanism of the perovskite materialBaTiO3 have been studied by using the density-functional theory within the full-potential linearaugmented plane wave (FP-LAPW) method. The valence and the bonding charge density,the density of states (DOS), the local DOS and the partial DOS were calculated toinvestigate the bonding mechanisms. The charge transfer, along with the bonding process,was analysed by using the atoms in molecules theory (AIM). Based on the analysis of thebonding and the topological characteristics, the evolution of the bonding strength according todifferent lattice strains and ion displacements along with the phase transition ofBaTiO3 is shown quantitatively. Moreover, the evolution of the spontaneous polarization ofBaTiO3 corresponding to the ion displacements is also discussed by a modern theory of polarizationin the present paper.

Phase-field model for epitaxial ferroelectric and magnetic nanocomposite thin films

A phase-field model was developed for studying the magnetoelectric coupling effect in epitaxial ferroelectric and magnetic nanocomposite thin films. The model can simultaneously take into account the ferroelectric and magnetic domain structures, the electrostrictive and magnetostrictive effects, substrate constraint, as well as the long-range interactions such as magnetic, electric, and elastic interactions. As an example, the magnetic-field-induced electric polarization in BaTiO3–CoFe2O4 nanocomposite film was analyzed. The effects of the film thickness, morphology of the nanocomposite, and substrate constraint on the degree of magnetoelectric coupling were discussed.