BaTiO3 Crystal Research Articles

Crystal growth and dielectric properties of BaTiO3 obtained in aluminoborosilicate glasses

The synthesis of invert glasses in the system Na2O/TiO2/BaO/Al2O3/B2O3/SiO2/Fe2O3 is reported for different [Na2O]/[Al2O3]-ratios and glass-former concentration less than 30mol%. During annealing in the glasses cubic and tetragonal BaTiO3 crystals are simultaneously crystallized as proved by X-ray diffraction. Scanning electron microscopy micrographs show that during isothermal heat-treatment globular crystals with sizes from 100nm to 1μm are formed. The dielectric properties of the glass-ceramics are studied at room temperature by impedance spectroscopy using two contact points measurement and gold electrodes. The impedance and the phase angle are measured in the frequency range from 0.1Hz to 1MHz. The obtained impedance spectra are simulated using an appropriate equivalent circuit in order to extract information on the bulk resistance and capacitance of the sample. Measurements of the capacitance at fixed frequencies are carried out and the dielectric constants are calculated. High dielectric constants in the order of 1000 at a frequency of f=13Hz are estimated, which increase with the increasing annealing times and decrease with increasing frequencies.

90-degree polarization switching in BaTiO3 crystals without domain wall motion

We report 90° polarization switching in a BaTiO3 crystal without domain wall (DW) motion by prefabricating samples with interlocking domains via compression. During electric re-poling of the depoled and aged crystals, 90° domain nucleation still exists, but 90° DW motion is inhibited by the strong constraints from surrounding domains, leading to DW-free 90° polarization switching. The measured coercive field of 500 V/mm for the DW-free 90° switching is close to the intrinsic values and much larger than that of 80 V/mm via 90° DW motion. Compared to the rather difficult domain-free 180° polarization switching in ultrathin films, 90° DW-free switching is easier.

Direct Molecular Dynamics Simulation of Electrocaloric Effect in BaTiO3

The electrocaloric effect (ECE) in BaTiO3 is simulated using two different first-principles based effective Hamiltonian molecular dynamics methods. The calculations are performed for a wide range of temperatures (30–900 K) and external electric fields (0–500 kV/cm). As expected, a large adiabatic temperature change, ΔT, at the Curie temperature, TC, is observed. It is found that for single crystals of pure BaTiO3, the temperature range where a large ΔT is observed is narrow for small external electric fields (<50 kV/cm). Large fields (>100 kV/cm) may be required to broaden the effective temperature range. The effect of crystal anisotropy on the ECE ΔT is also investigated. It is found that applying an external electric field along the [001] direction has a larger ECE than those along the [110] and [111] directions.

Comparative Study of the Signal-to-Noise Ratio and Gain in Photorefractive Materials

We calculate the dependence of the signal-to-noise ratio and gain on the angle α between the pump and signal beams and the beam ratio β in Cu-doped potassium-sodium-strontium-barium niobate (Cu:KNSBN) crystal and compare them with the experimental results available in the literature. We find good qualitative agreement between the calculated and experimental results. Also we study variations of SNR and gain with α and β in BaTiO3 crystal. Experimental data for this crystal are not available.

Unusual domain configurations and local piezoresponse in the [720]‐cut BaTiO3 single crystal

AbstractThe domain configurations and local piezoresponse property of the [720]‐cut BaTiO3 single crystal and [001]‐oriented BaTiO3 crystal were investigated by high‐resolution piezoresponse force microscopy. Large differences in their surface topography features, domain configurations and local piezoresponse were found between [720]‐cut and [001]‐oriented BaTiO3 crystals. The large surface bending angle due to ferroelastic domain walls leads to a high strain energy appearing in the [720]‐cut BaTiO3, further resulting in unique band‐like topographic features, needle domains for stress compensation and locally ultrahigh piezoelectric response as well. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

THE CONDITION OF THE COMBINATION FOR THE CRYSTAL BaTiO&lt;sub&gt;3&lt;/sub&gt;

For crystals of BaTiO 3 type due to superspace symmetry conception over all vectors k i of Brillouin zone full vibrational images were obtained and the analysis of correlation combination was carried out. Within the framework of proposed methods the vibrational branches of phonon spectrum and contribution to symmetry of each crystal atom were determined.

Piezoelectric anisotropy of orthorhombic ferroelectric single crystals

In the frame of thermodynamic approach, it is shown that all the admissible values of the d33, d32, and d31 piezoelectric moduli of any orthorhombic (mm2) single crystal in the 3-dimensional (d33, d32, d31) space lie within a restricted area having the form of ellipsoid. The main parameters of this ellipsoid (the aspect ratios and the angles characterizing its orientation) depend only on the elastic constants of the crystal. Using the developed approach, the areas of the allowable values of piezoelectric moduli have been determined for six crystals: single-domain KNbO3 and 0.27Pb(In0.5Nb0.5)O3-0.40Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystals possessing true orthorhombic symmetry and four polydomain macroscopically pseudoorthorhombic crystals—tetragonal BaTiO3 and PbTiO3 crystals with laminate 90° domain structure as well as rhombohedral 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 and 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 crystals, poled along the [011] direction of the prototype cubic cell. Four crystals from this set possess negative values of the longitudinal Poisson's ratio and are thus partially auxetics.

Polarization rotation theory for field-induced-phase transitions in BaTiO3 single crystal

We have proposed the polarization rotation theory to understand the underlying physics of the large piezoelectric effect in ferroelectric crystals by referring to the coherent rotation model in ferromagnetism. When both the electric field energy and crystalline anisotropy energy are taken into account, the polarization in BaTiO3 crystal can be rotated toward the field direction. The numerical results are in agreement with the experimental observations and have indicated the highly anisotropic polarization rotations and the field-induced-phases with different symmetries in the crystal. This theory is helpful for understanding the polarization reversal and the electromechanical effect in ferroelectric materials.

Ferroelectric phase transitions and electromechanical properties of barium titanate and lead titanate crystals under uniaxial and shear stresses: a thermodynamic analysis

Ferroelectric phase transitions and electromechanical properties of BaTiO3 (BT) and PbTiO3 (PT) crystals under uniaxial and shear stresses are investigated using the Landau–Devonshire phenomenological approach. The results show that (1) the Curie temperature of BT and PT crystals increases with increasing stress; (2) at room temperature, no ferroelectric–ferroelectric phase transition is induced by uniaxial stress along the [1 0 0]c direction for the PT crystal, while the orthorhombic phase is the ultimate stable state for BT and PT crystals under uniaxial stress along the [0 0 1]c direction and shear stress; (3) shear stress induces a temperature-independent morphotropic phase boundary in tetragonal phase BT and PT crystals; (4) the dielectric and piezoelectric properties are closely related to the phase transition induced by external stresses, where nonlinearity is observed owing to higher order terms of free energy.

Analysis for the nonlinear electro-optic modulation effect of BaTiO3 crystal thin-film waveguide modulators

Quadratic-order electro-optic (EO) modulation of BaTiO3 crystal thin-film devices has stimulated increasing research on high-bandwidth modulators and other functions. The quadratic-order EO modulation is created by an outside electric field with respect to the EO coefficient r42 or r51. In this work, the entire changing process of refractive index ellipsoid of BaTiO3 crystal driven by an outside electric field is investigated, and two nonlinear EO modulation processes of quadratic and quartic nonlinearities are found for defining the relationship between drive voltage and interaction length. Theoretical investigation shows the dominations of two nonlinear processes—the quadratic and quartic modulations strongly depend on the birefringence, the electric field intensity applied, and the interaction length. The condition for defining the two effective high-order nonlinear modulation processes is that at 1550 nm wavelength when the absolute birefringence is close to 0.001, the quadratic model is challenged and instead the quartic one is more effective. An absolute birefringence of 0.001 can make the r51 of 250 pm/V meet a half-wave drive voltage of 5 V and an interaction length of 1 mm, which has the same role as 600 pm/V r51 value at an absolute birefringence of 0.007. Such an important finding is also verified by the simulation results of optical output operations of the EO modulator. This work has theoretically explained an incredible phenomenon reported that the dramatically different values of an effective EO coefficient are measured for the same device sample at different experimental conditions: the electric field intensity applied and axis-orientation of crystal.

Simulations for dual-rail driven electro-optic modulators of BaTiO3 crystal thin-film waveguides

In this work, a dual-rail EO modulator structure is presented with the advantages of extremely high electro-optic (EO) coefficient r51 of BaTiO3 crystal, the quadratic modulation effect and the thin-film waveguide structure where electric fields are applied at both transverse and horizontal directions of optical beam propagation to create a dual-rail driven modulation effect to the refractive index of optical channel. A new theoretical model of the quadratic modulation effect to the dual-rail driven regime is proposed. The dependences of Vπ2L on the physical parameters of devices such as the two electrode gaps, the r51 value and the birefringence of BaTiO3 crystal thin-film are simulated, then the intrinsic relationships among the half-wave voltage Vπ, interaction length L, EO coefficient r51, birefringence Beo and electrode gap G are investigated. As an illustration, for an extremely small L value of 1mm, <6.0V Vπ values correspond to 600pm/V r51, −0.007 Beo and 7.5μm G. Finally, the challenges and possibilities to the new regime of dual-rail driven EO modulators are discussed.

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.

Nontrivial behavior of Tc at the small electric field in BaTiO3 crystals, detected by means of acoustic emission

Cubic–tetragonal phase transitions of [100]-oriented BaTiO3 crystals have been studied by means of an acoustic emission (AE) method, under an external electric field. The Curie temperature (Tc) reveals a nontrivial behavior at the small field, namely, it initially decreases with enhancement of the field, attains a minimum at the threshold field Eth = 0.256 kV cm−1, accompanied by the AE count rate , and then starts increasing with a rate of 1.5 K m kV−1 as the field is enhanced. Such nontrivial behavior of Tc is explained as due to the presence of polar nanoregions, recently revealed in BaTiO3 crystals (Ko et al 2011 Phys. Rev. B 84 094123).

Large and electric field tunable superelasticity in BaTiO3 crystals predicted by an incremental domain switching criterion

Superelasticity is very common in shape memory alloys but is rather difficult to realize in ferroelectric ceramics and had never appeared in normal ferroelectric single crystals. Here we show that guided by a proposed incremental 90° domain switching criterion, large and electric-field-tunable superelastic strains up to 0.85% has been realized in a specially poled BaTiO3 crystal cube via compression loading/unloading with a positive dc bias electric field along the poling direction. Moreover, the tunable superelasticity has a large damping factor of up to 0.76, which is very promising in intelligent damping devices.

Properties of epitaxial BaTiO3 deposited on GaAs

Single crystal BaTiO3 (BTO) has been grown epitaxially on GaAs using molecular beam epitaxy with a 2 unit cell SrTiO3 nucleation layer. The oxide film is lattice-matched to GaAs through an in-plane rotation of 45° relative to the (100) surface leading to c-axis orientation of the BaTiO3. X-ray diffraction confirmed the crystallinity and orientation of the oxide film with a full width half maximum of 0.58° for a 7.5 nm thick layer. Piezoresponse force microscopy was used to characterize the ferroelectric domains in the BaTiO3 layer, and a coercive voltage of 1–2 V and piezoresponse amplitude ∼5 pm/V was measured.

Low Frequency Raman Scattering in BaTiO3 Crystal

The central peak (CP) in Raman scattering in BTO crystals was investigated in wide spectral and temperature ranges. The identical CP properties both in the VV and the VH scattering geometries, best fitting of low-frequency Raman spectra by the Lorentz function, and obtaining the typical temperature dependences for the CP amplitude and width support the relaxation nature of CP in the BTO crystals.

Divergence of dielectric permittivity near phase transition within ferroelectric domain boundaries

Phase-field simulations based on Ginzburg–Landau–Devonshire model were utilised to demonstrate and quantify the enhancement of the dielectric permittivity of multidomain rhombohedral BaTiO3 crystal in the vicinity of the Bloch-type to Ising-type phase transition within 180° domain boundaries with crystallographic orientation. The phase transition is driven by compressive mechanical stress applied in the plane perpendicular to the spontaneous polarisation direction. Simulations reveal a classical Curie–Weiss behaviour of the transverse component of dielectric permittivity, expected in the vicinity of a second-order phase transition.

Size dependent polarization reversal at nanoscale metal-ferroelectric interfaces

Ferroelectric oxides possess a unique set of physical properties that have not been maximally exploited due to a lack of understanding of the origins of the switching behavior. Currently, controversy exists over whether switching in ferroelectric oxides is due to polarization or defect mediated switching. Here, we use ultra-high vacuum scanning tunneling microscopy and atomic force microscopy to investigate the process of polarization reversal and to assess the effect of the electronic structure and conductance on the switching behavior of single crystal BaTiO3 (001). Measurements of the local density of states revealed the surface switching behavior was initially due to polarization and that a transition occurred to defected mediated switching after repeated switching cycles. Atomic force microscopy investigations of the size effects at nanoscale Au-BaTiO3 (001) interfaces revealed asymmetric polarization reversal at large interfaces with a convergence to symmetric behavior as the size scale decreased, in agreement with the tunneling-based scanning tunneling microscopy technique.

Phase transitions and electromechanical properties for barium titanate and lead titanate ferroelectric crystals under one-dimensional shock wave compression

Ferroelectric phase transitions and electromechanical properties of BaTiO3 (BT) and PbTiO3 (PT) crystals under one-dimensional shock wave compression were investigated using Landau-Ginzburg-Devonshire phenomenological approach. The results showed that the Curie temperature of both BT and PT increased with increasing pressure. Under highest shock wave compression, the orthorhombic phase was the stable state for BT, while no ferroelectric-ferroelectric phase transition was induced for PT. At room temperature, the electromechanical parameters for PT and BT were found to decrease with increasing one-dimensional compression, except for the dielectric susceptibility ε22 and piezoelectric coefficient e24 of tetragonal BT. The variations of dielectric and piezoelectric parameters were analyzed according to the elastic Gibbs free-energy.

Effective Hamiltonian methods for predicting the electrocaloric behavior of BaTiO3

The perovskite crystal BaTiO3 is modeled using a first-principles based effective Hamiltonian and molecular dynamics simulations are performed to estimate the pyroelectric response. The electrocaloric temperature change, ΔT, is calculated for different temperatures and externally applied electric fields. It is found that it is possible to achieve a large ΔT, around 5–6K, for a relatively small electric field gradient, less than 100kV/cm, if the applied fields have a small absolute magnitude.