BaTiO3 Single Crystals Research Articles

Control of Ferroelectric Aging by Manipulating Point Defects

In the present work, we systematically studied the aging effect of both ferroelectric single crystals and polycrystals to study how to control aging effect. We found that such hybrid-doped BaTiO3 single crystals showed obvious aging effect only when the concentration of the acceptor K+ is higher than that of the donor; when the donor F− concentration is higher than the acceptor K+, the K-F doped BaTiO3 showed almost no aging effect. Similar results were obtained in La-Mn doped BaTiO3 polycrystals. With the increase of the concentration of donor La3+ in 0.5%Mn-BaTiO3 ceramics, the aging effect gradually becomes weaker and finally disappears. Our result suggests that donor doping is an effective way of controlling the aging effect.

Absence of Correlation Between Atomic Lattice Steps and 180° Domain Boundaries in BaTiO3 Single Crystals

By performing the high resolution observation of the surface topography and measurement of the surface potential of the ferroelectric domain structures in an ultra-high-vacuum (UHV), we found that there is no correlation between the surface atomic steps and the ferroelectric 180° domain boundaries.

Three-dimensional ferroelectric domain imaging of epitaxial BiFeO3 thin films using angle-resolved piezoresponse force microscopy

Here we introduce angle-resolved piezoresponse force microscopy (AR-PFM), whereby the sample is rotated by 30° increments around the surface normal vector and the in-plane PFM phase signals are collected at each angle. We obtained the AR-PFM images of BaTiO3 single crystal and cube-on-cube epitaxial (001) BiFeO3 (BFO) thin film on SrRuO3/SrTiO3 substrate, and confirmed that the AR-PFM provides more unambiguous information on the in-plane polarization directions than the conventional PFM method. Moreover, we found eight additional in-plane polarization variants in epitaxial BFO thin films, which are formed to mitigate highly unstable charged domain boundaries.

Lateral signals in piezoresponse force microscopy at domain boundaries of ferroelectric crystals

In piezoresponse force microscopy a lateral signal at the domain boundaries is occasionally observed. In recent years, a couple of experiments have been reported and varying explanations for the origin of this lateral signal have been proposed. Additionally, elaborated theoretical modeling for this particular issue has been carried out. Here we present experimental data obtained on different crystallographic cuts of LiNbO3, BaTiO3, and KTiOPO4 single crystals. We could thereby rule out some of the explanations proposed so far, introduce another possible mechanism, and quantitatively compare our results to the existing modeling.

The Effect of Antinotches on Domain Wall Mobility in Single Crystal Ferroelectric Nanowires

Changes in domain wall mobility, caused by the presence of antinotches in single crystal BaTiO(3) nanowires, have been investigated. While antinotches appeared to cause a slight broadening in the distribution of switching events, observed as a function of applied electric field (inferred from capacitance-voltage measurements), the effect was often subtle. Greater clarity of information was obtained from Rayleigh analysis of the capacitance variation with ac field amplitude. Here the magnitude of the domain wall mobility parameter (alpha) associated with irreversible wall movements was found to be reduced by the presence of antinotches--an effect which became more noticeable on heating toward the Curie temperature. The reduction in this domain wall mobility was contrasted with the noticeable enhancement found previously in ferroelectric wires with notches. Finite element modeling of the electric field, developed in the nanowires during switching, revealed regions of increased and decreased local field at the center of the notch and antinotch structures, respectively; the absolute magnitude of field enhancement in the notch centers was considerably greater than the field reduction in the center of the antinotches and this was commensurate with the manner in, and degree to, which domain wall mobility appeared to be affected. We therefore conclude that the main mechanism by which morphology alters the irreversible component of the domain wall mobility in ferroelectric wire structures is via the manner in which morphological variations alter the spatial distribution of the electric field.

Area fraction quantification of ferroelectric domain orientations in BaTiO3 using piezoresponse force microscopy

Understanding the domain structure of ferroelectric ceramics is very important to develop sound knowledge of the influence of the microstructure on the macroscopic properties. To proceed in this direction, experimental tools are necessary in order to quantify the domain patterns in ferroelectrics. This study on BaTiO3 single crystals exemplifies how vector piezoresponse force microscopy can be used to obtain statistical information about domain directions.

Optimal configuration of microstructure in ferroelectric materials by stochastic optimization

An optimization procedure determining the ideal configuration at the microstructural level of ferroelectric (FE) materials is applied to maximize piezoelectricity. Piezoelectricity in ceramic FEs differs significantly from that of single crystals because of the presence of crystallites (grains) possessing crystallographic axes aligned imperfectly. The piezoelectric properties of a polycrystalline (ceramic) FE is inextricably related to the grain orientation distribution (texture). The set of combination of variables, known as solution space, which dictates the texture of a ceramic is unlimited and hence the choice of the optimal solution which maximizes the piezoelectricity is complicated. Thus, a stochastic global optimization combined with homogenization is employed for the identification of the optimal granular configuration of the FE ceramic microstructure with optimum piezoelectric properties. The macroscopic equilibrium piezoelectric properties of polycrystalline FE is calculated using mathematical homogenization at each iteration step. The configuration of grains characterized by its orientations at each iteration is generated using a randomly selected set of orientation distribution parameters. The optimization procedure applied to the single crystalline phase compares well with the experimental data. Apparent enhancement of piezoelectric coefficient d33 is observed in an optimally oriented BaTiO3 single crystal. Based on the good agreement of results with the published data in single crystals, we proceed to apply the methodology in polycrystals. A configuration of crystallites, simultaneously constraining the orientation distribution of the c-axis (polar axis) while incorporating ab-plane randomness, which would multiply the overall piezoelectricity in ceramic BaTiO3 is also identified. The orientation distribution of the c-axes is found to be a narrow Gaussian distribution centered around 45°. The piezoelectric coefficient in such a ceramic is found to be nearly three times as that of the single crystal. Our optimization model provide designs for materials with enhanced piezoelectric performance, which would stimulate further studies involving materials possessing higher spontaneous polarization.

Ferroelectric BaTiO3 single crystal under superstrong electric fields up to 55 MV/m: A comparative experimental and theoretical study

We investigated the effect of huge electric field up to E=55 MV/m on tetragonal ferroelectric phase of BaTiO3 single crystal. Both lattice parameters and the dielectric susceptibility along the polar axis were determined. The induced polarization shows a continuous increase up to 20% of the spontaneous polarization. The longitudinal d33 and transverse d31 piezoelectric coefficients were also determined. The experimental data are described by a phenomenological approach. Interestingly, an intermediate critical electric field value of E∼25 MV/m was evidenced suggesting that the physics below and above this value are different.

Crystal Structure and Dielectric Characterization of a (SrTiO3/BaTiO3) n Multilayer Film Prepared by Radio Frequency Magnetron Sputtering

(SrTiO3/BaTiO3) n multilayer films with Pt bottom and top electrodes have been prepared by a double target radio frequency (RF) magnetron sputtering, and their dielectric properties have been characterized as a function of temperature, frequency, bias voltage, and applied voltage. The X-ray diffraction (XRD) pattern reveals that the deposited (SrTiO3/BaTiO3) n multilayer films have a designed modulation. The interfaces within the multilayer films appear smooth and dense without any microcracks, and the adhesion is very good. The dielectric constant of the (SrTiO3/BaTiO3) n multilayer film increases with increasing layer number (n), and the leakage current density is less than 1 × 10−8 A·cm−2 for the applied voltage less than 5 V for the 450-nm-thick (SrTiO3/BaTiO3) n multilayer films. The remanent polarization (P r ) and the coercive field (E c ) of the 350-nm-thick (SrTiO3/BaTiO3)4 multilayer films are 7 μC·cm−2 and 60 kV·cm−1, respectively, exhibiting ferroelectricity. (SrTiO3/BaTiO3)4 multilayer films have a high E c and a lower P r , as compared with the bulk BaTiO3 single crystal. The 450-nm-thick (SrTiO3/BaTiO3)4 multilayer films have a leakage current density-voltage characteristic, which makes them suitable for application in DRAMs capacitors.

The influence of notches on domain dynamics in ferroelectric nanowires

The extent to which notches inhibit axial switching of polarization in ferroelectric nanowires was investigated by monitoring the switching behavior of single crystal BaTiO3 wires before and after patterning triangular notches along their lengths. Static zero-field domain patterns suggested a strong domain-notch interaction, implying that notches should act as pinning sites for domain wall propagation. Surprisingly though, notches appeared to assist, rather than inhibit, polar switching. The origin of this effect was rationalized using finite element modeling of the electric field distribution along the notched wire; it was found that the air gap associated with the notch acted to enhance the local field, both in the air, and in the adjacent region of the ferroelectric. It seems that this local field enhancement outweighs any pinning interactions.

Influence of structural transitions of BaTiO3 on the magnetic properties of Fe nanoparticles

Ferroelectric BaTiO3 single crystals with (001) orientation were implanted with Fe at room temperature with an energy of 100 keV and a fluence of 1×1017 cm-2. For the implanted crystals, the analysis of the magnetic properties shows that Fe nanoparticles are formed and display characteristic superparamagnetic behaviour. The thermal dependence of the nanoparticles magnetisation shows the signature of the structural phase transitions of BaTiO3 with changes in the magnetisations values and thermal hysteresis observed at related temperatures.

Influence of dc-bias on phase stability in Mn-doped Na0.5Bi0.5TiO3-5.6 at. %BaTiO3 single crystals

Mn-doped Na0.5Bi0.5TiO3-5.6 at. %BaTiO3 (Mn:NBT-5.6%BT) single crystals were grown by a top-seeded solution growth method. Tetragonal and rhombohedral phases were found to coexist in the as-grown condition. The dielectric and structural properties were studied as a function of temperature under dc electrical bias. An induced phase stability change from rhombohedral to tetragonal phases occurred under an electric-field applied along the ⟨001⟩ direction.

Ferroelectric BaTiO3 Nanowires by a Topochemical Solid-State Reaction

The possible existence of a new kind of ferroelectric order and the need to explore domain arrangement in ferroelectric nanostructures has stimulated an increasing activity on the growth of ferroelectric nanowires. In the present study, single crystal BaTiO3 nanowires with tetragonal structure were obtained by an original solid-state process using layered titania nanowires coated with BaCO3 nanocrystals as reactive templates. Formation of BaTiO3 occurs at 700 °C by a topochemical reaction. Consequently, the initial morphology of the titania nanowires is retained in the final product. Piezoresponse force microscopy measurements show a strong piezoactivity and stripe domain patterns with domain width of 20−50 nm, predominant in-plane response and 90° domain walls. The proposed synthesis method is quite general and might be adapted to the fabrication different ferroelectric and nonferroelectric oxide nanowires.

Enhanced piezoelectric and ferroelectric properties in Mn-doped Na0.5Bi0.5TiO3–BaTiO3 single crystals

High piezoelectric and ferroelectric properties have been found in Mn-doped Na0.5Bi0.5TiO3–BaTiO3 single crystals, which were grown by a top-seeded solution method. The electrical resistivity, dielectric constant, and ferroelectric and piezoelectric properties were all found to be notably enhanced by Mn. The piezoelectric constant d33 and electromechanical coupling coefficients kt and k31 were found to be as high as 483 pC/N, 0.56, and 0.40, respectively. These values are much higher than those previously reported for Pb-free piezoelectric crystals, demonstrating the real potential for alternative lead-free systems for sensor and piezoelectric applications.

X-ray Diffraction Topography of BaTiO3 at Phase Transition Temperature

We performed X-ray diffraction topography analysis on a BaTiO3 single crystal with high-coherence synchrotron X-rays. Since the domain configuration of the BaTiO3 single crystal was unstable and fluctuated with temperature, an excellent temperature control system was used for domain observation. We used a milli-Kelvin (mK)-stabilized cell, which can control BaTiO3 crystal temperature to within ±1 mK. By combining the coherent X-rays and the mK-stabilized cell, We detected the domain configuration very sensitively during phase transition. The domain configuration changed markedly at the transition temperature. The low-temperature tetragonal domain fluctuated markedly before the long-range-order structure changed from tetragonal to cubic. The ferroelectric-to-paraelectric transition occurred in two steps; first, the domain configuration changed into a tetragonal phase, and then, the average structure changed into a cubic structure.

Piezoelectric Properties near the Tricritical Point on KF-Doped BaTiO3 Single Crystal

The temperature dependence of the piezoelectric constant d33, electromechanical coupling factor k33, dielectric constant ε33T and elastic compliance s33E for a single crystal of KF-doped barium titanate with a KF content near the tricritical point (TCP), Ba0.91K0.09TiO2.91F0.09 (KF-BT/0.09), was measured by a resonance–antiresonance method in a temperature range between 270 and 340 K. The single crystals used were grown by a KF-flux method and the largest single crystal was a cube of 5 mm size. A large piezoelectric constant and a large dielectric constant were obtained at 300 K: d33 = 300 pC/N, k33 = 0.59, and ε33T = 3,000. As the temperature increases, ε33T gradually increases toward TC but does not show any discontinuous changes at TC = 329 K; moreover, s33E and d33 increase with temperature between 270 and 310 K. However, above 310 K, they decrease toward TC. The fluctuation of the order parameter near the TCP induces these peculiar behaviors.

Hydrothermal Synthesis of BaTiO<sub>3</sub> Nanotubes on Ti Substrates

A novel, low-temperature two-step synthesis method for producing BaTiO3 thin films patterned in the form of nanotubes on Ti substrates is reported. Firstly, the Ti substrate is anodized to produce a surface layer of amorphous TiO2 nanotube arrays. Secondly, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)2, where the nanotube arrays serve as templates for their hydrothermal conversion to single-crystal BaTiO3 thin film. This opens the possibility of tailoring the nanotube arrays and their combinations in the hydrothermal bath, to produce ordered, patterned thin film structures of various Ti containing ceramics.

Experiments and first principles calculations on the effects of hydrogen on the optical properties of ferroelectric materials

The effects of hydrogen on the optical properties of lead zirconate titanate (PZT) ceramics and BaTiO3 single crystals have been investigated. The experimental results showed that the color of BaTiO3 single crystals changed from light to dark after charging of hydrogen in NaOH solution at room temperature and in H2 gas at high temperature, and then, restored to light color after outgassing in the air, which were the same as PZT-5H ceramics reported earlier. Measurement of the absorbance indicated that hydrogen increased the absorbance within the visible spectrum for both PZT ceramics and BaTiO3 single crystals. The first principles calculations for Pb(Zr0.5Ti0.5)O3 and BaTiO3 showed that hydrogen increased the absorbance within the infrared and visible spectral region and the absorbance increased with the rise of hydrogen concentration. Density of states (DOS) researches indicated that hydrogen changed the DOS of the outer shell electrons, which caused the change of absorbance spectrum.

Surface Instability in High Surface Area Complex Oxides: BaTiO3 Study

High quality BaTiO3 powders that were synthesized with hydrothermal and solid state methods are characterized with respect to surface chemistry. Different characterization techniques are used to obtain a physical picture for the BaTiO3 powders with respect to different synthesis routes and thermal histories. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) are used to understand the BaTiO3 powders after heat and humidity treatments. Formation of amorphous and crystalline BaCO3 in local heterogeneous regions depletes the surrounding surface of Ba ions to create larger areas that are Ti-rich. BaCO3 formation and adventitious carbon adsorption occur extremely quickly on the surface of crushed single-crystal BaTiO3 powder, but for manufactured powders, the degree of carbonate formation and the impact on surface stoichiometry varies with thermal history.

Investigation of Clean Ferroelectric Surface in Ultra High Vacuum (UHV): Surface Conduction and Scanning Probe Microscopy in UHV

We discuss the controversies related with an intrinsic screening effect of the ferroelectric surface and report experiments of electron (e −)/hole (h +) layer on the clean surface of insulating pure BaTiO3 single crystals in ultra high vacuum, which is a follow-up of the first report on the intrinsic surface carrier layer on ferroelectric [Y. Watanabe et al., Phys. Rev. Lett. 86, 332 (2001)]. The experiments verify that both accumulation and inversion occur and the surface carrier layer is intrinsic, i.e., mainly due to spontaneous polarization P S not to impurities or defects. We show also that the surface carrier layer is consistent with the 180° domains, the theory for the polarization (D-E) curves of ferroelectric FET [S. L. Miller and P. J. McWhorter, J.Appl. Phys. 72, 5999 (1992)], the invisibility of the carrier layer in the dynamic response of ferroelectric. Especially, the electrostatic and the piezoelectric-response images by UHV-AFM show directly an intrinsic screening effect in 180° domains.