BaTiO3 Single Crystals Research Articles

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.

Ferroelectric Phase Transition in Cu-doped BaTiO3 Crystals

The paper examines the ferroelectric-paraelectric phase transition in Cu:BaTiO3 single crystals. Using thermo-currents and dielectric measurements, we found for pure samples the phase transition temperature to be close to Curie temperature (Tc=120°C) with an anisotropy of the dielectric constantε.The lowering of temperature Tm, corresponding to the maximum of pyroelectric signal, with the increase of concentration of impurities is confirmed by measurements of ε. Moreover, the e(T) curves show progressive broadening as well as higher peak with the increase of impurity concentration, and the transition becomes more and more diffuse. The same effect occurs when the samples are subjected to a laser irradiation (λ=5145Ǻ). During annealing, crystals lose copper and Tm is thereafter observed to increase again. BaTiO3 is a displacive ferroelectric (having high permittivity k-values) which undergoes a first order phase transition. Ions substitutions have an effect on the lattice dynamics attributed to charge transfer to Ti and a lowering of elastic forces in BaTiO3. Kewwords: Ferroelectric transition; BaTiO3 single crystals; Thermo-currents; Dielectric constant. © 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v1i2.1876

Single crystal growth in PMN-PT and PMN-PZT

Single crystal growth of lead-based piezoelectric ceramics Pb(Mg1/3Nb2/3)0.68Ti0.32O3 (PMN-32PT) and Pb(Mg1/3Nb2/3)0.42(Ti0.638Zr0.362)0.58O3 (PMN-37PT-21PZ) ceramics via templated grain growth (TGG) was investigated. (001)- and (111)-oriented BaTiO3 (BT) single crystals and (001)-oriented SrTiO3 (ST) single crystals (of approximately 2.5 × 2.5 × 1 mm) were utilized as seeds for the growth experiments. The piezoelectric single crystals were produced in a process that involves at first hot pressing of single crystal in cold isostatically pressed ceramics followed by subsequent sintering of the samples. Growth of (001)-oriented single crystals with BT seeds was observed in both PMN-32PT and PMN-37PT-21PZ matrices. The measured growth lengths were up to 140 and 65 μm, respectively. The grown (001)-oriented single crystals grown were rectangular. The measured growth lengths of the pyramidal-shaped (111) BT single crystals were up to 1 mm, which is much larger than the growth lengths of the (001) single crystals. Experiments on (001) ST-seeded single crystals were not successful. No single crystal growth was observed due to the dissolution of the ST single crystals in the PMN-PZT matrix. The differences were explained by defect-chemical considerations.

Dynamic ferroelectric hysteresis scaling of BaTiO3 single crystals

The scaling behavior of the dynamic hysteresis of ferroelectric BaTiO3 single crystals was investigated. Two sets of the scaling relation of hysteresis area ⟨A⟩ against frequency f and field amplitude E0 were clearly established. Above the coercive field, the scaling took a form of ⟨A⟩∝f−0.195E00.950. On the other hand, the scaling in the form of ⟨A⟩∝f1.667E0−2.804E04.157 was obtained under subcoercive field condition. While these scaling relations were generally comparable to previously reported ones, it was found that the f and E0 exponents depended on E0 and f, respectively, which was in contrast to the prior theoretical prediction and experimental investigations.

Artificially controlled magnetic domain structures in ferromagnetic dots∕ferroelectric heterostructures

A variation in the magnetization and magnetic domain structures of epitaxial Fe dots on a single crystal BaTiO3 substrate is demonstrated in association with the structural phase transition of ferroelectric BaTiO3. The temperature dependent magnetization of Fe dots drops suddenly at 282K and increases again at 189K with decreasing temperature. The variations clearly correspond to the successive structural phase transitions of BaTiO3 from tetragonal to orthorhombic phases and from orthorhombic to rhombohedral phases. After a thermal cycle between room temperature and 150K passing through these phase transitions, the initial magnetic domain structure of Fe dots with an enclosed magnetic flux structure changes to a single-domain-like structure due to interfacial strain between Fe and BaTiO3 arising from possible switching of c-axis orientation of BaTiO3 substrate.

Monoclinic MC phase in (001) field cooled BaTiO3 single crystals

We report here the finding of a new phase in BaTiO3 single crystals. High precision x-ray diffraction investigations of (001) field cooled crystals have shown the presence of a monoclinic MC phase for temperatures below 300 K. This MC phase is shown to be stable upon removal of the electric field. The results demonstrate the presence of structurally bridging low symmetry phases that lie between tetragonal and rhombohedral ones in this classic perovskite system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.

Magnetic anisotropy modulation of magnetite in Fe3O4/BaTiO3(100) epitaxial structures

Temperature dependent magnetometry and transport measurements on epitaxial Fe3O4 films grown on BaTiO3(100) single crystals by molecular beam epitaxy show a series of discontinuities, due to changes in the magnetic anisotropy induced by strain from the different crystal phases of BaTiO3. The magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO3 at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with the magnetoelastic anisotropies. These results demonstrate the possibility of using the piezoelectric response of BaTiO3 to modulate the magnetic anisotropy of magnetite films.

Structure study of single crystalBaTiO3 nanotube arrays produced by the hydrothermal method

High aspect ratio BaTiO3 nanotube arrays with single crystal structure were fabricated by the hydrothermal method at low temperature(150 °C). Numerous structure study methods, including x-ray diffraction (XRD), Raman spectroscopy,transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), and x-rayphotoelectron spectroscopy (XPS), were used to investigate the structure of single crystalBaTiO3 nanotube arrays. TEM observation shows thatBaTiO3 nanotubes have identical crystallographic orientation through theirgrowth directions. EPR and XPS studies show that the obtainedBaTiO3 nanotubes contain perceptible oxygen vacancies. Those oxygen vacancies are responsible forthe observed green emission band at 545 nm (2.27 eV) detected by photoluminescencestudy.

Study of the dipole rotation path of BaTiO3 single crystal based on dielectric properties in structure phase transition

The temperature-dependence of dielectric-constant of BaTiO3 single crystals in 〈001〉 direction is measured under different voltages and frequencies. The crystal experiences rhombohedral-orthorhombic-tetragonal phase transition with the increase of temperature. Base on the assumption of dipoles rotation and the experimental results of dielectric constant, a model is proposed, which holds that the dipoles rotation path can be inferred by the dielectric properties of the adjacent structure phase of BaTiO3. The dipoles rotation paths of rhombohedral, orthorhombic and tetragonal phases are given. The influences of bias dc electric field on the dipoles rotation path are discussed.

Reorientation of (MnTi″−VO••)× defect dipoles in acceptor-modified BaTiO3 single crystals: An electron paramagnetic resonance study

The effect of external electric fields on the orientation of (MnTi″−VO••)× defect dipoles in ferroelectric BaTiO3 single crystals and its interplay with the domain structure were investigated by means of electron paramagnetic resonance (EPR) spectroscopy and optical microscopy. The results show that in specimens aged in the ferroelectric state for a defined time, so-termed ferroelectrically aged, the (MnTi″−VO••)× defect dipoles orient along the direction of spontaneous polarization and follow the domain switching upon poling with correspondingly high electric fields. A comparison of the EPR signal in poled aged single-domain samples to that in naturally aged multidomain samples indicates a similar reorientation process of the defect dipole, which means that dipole reorientation rather requires long time, thermal energy, and high electric fields, i.e., more energy.

Nanoindentation-induced plastic deformation and fracture behavior difference between a- and c-domains of BaTiO3 single crystal

The plastic deformation and fracture behavior of individual a- and c-domains of (001) oriented BaTiO3 single crystal are studied with nanoindentation and atomic force microscopy. Consistent with previous observations in rocksalt and perovskite crystals, square-shaped pileups directly surround the residual indents, and rosette arm patterns extend beyond these pileups. These features have been ascribed to dislocation activities on the {110}⟨11¯0⟩ slip systems induced by nanoindentations. We observed rosette screw arms only in c-domains, inside which 90° ac-domain switching is confirmed. We conclude that indentation-induced cracks on {110}90 planes most likely nucleate by dislocation pileups on two neighboring {110}45 planes, which create a sessile dislocation. Significantly shorter cracks in the c-domain under the same indentation load suggest a higher apparent toughness of the c-domain. However, we attribute the different crack lengths to the lower crack driving force resulting from indentation-induced plasticity in c-domains rather than an inherent difference in the crack growth resistance.

Domain switching contribution to piezoelectric response in BaTiO3 single crystals

Piezoelectric responses of barium titanate single crystals are investigated along the [720] and [111] directions, respectively, in order to verify the ultrahigh piezoelectric constant (2000pC∕N) reported in a previous study [Appl. Phys. Lett. 86, 012905 (2005)]. The results suggest that electric-field-induced strain can be largely enhanced by the domain switching in barium titanate single crystal along the [720] direction; however, the piezoelectric response under small field measurement has not been enhanced as much as expected because domain switching is a nonlinear and irreversible process.

Uniaxial Pressure Effect on the Dielectric Properties of the BaTiO3 Single Crystals

Effect of the uniaxial pressure (0–1000 bars) on the dielectric properties of the BaTiO3 single crystals was studied. It was shown that the external stress significantly influences these properties. This includes shift of the phase transformation, diffuseness of the permittivity characteristics and reduction of the thermal hysteresis. These effects can be connected with a change in the domain structure, change of distances among the ions and change in the defect density under the action of external stress. Some thermodynamic parameters of the phase transformation were also evaluated. It was concluded, that the uniaxial pressure causes similar effects as the hydrostatic pressure.

Bipolar Carrier (e −/h +) Layer on Clean Surface of Insulating BaTiO3 Crystal Intrinsic to Ferroelectrics

We report experimental observation of electron (e −)/hole (h +) layer on the clean surface of insulating pure BaTiO3 single crystals in ultra high vacuum (UHV < 10−8 Pa). To our knowledge this is the first report of the bipolar surface carrier layer by the field effect on any oxide. The experiments here verify that both accumulation and inversion occur and the surface carrier layer is intrinsic, i.e., due to spontaneous polarization P S not to impurities and defects.

Direct observation of two 90° steps of 180° domain switching in BaTiO3 single crystal under an antiparallel electric field

Domain-switching in BaTiO3 single crystal under an antiparallel electric field was investigated in this paper by polarized light microscope. It was found that 180° domain-switching consisted of two 90° switching steps. The polarization reversal of domains took place when an antiparallel electric field was applied to the BaTiO3 single crystal. The domain-switching process was different under different field intensities. Under a low field, all domains switched 180° through two 90° domain-switching steps. However, under a high field, only some 90° domains were nucleated in the initial period and subsequently all domains switched to the direction of the external field quickly.

Hydrothermal synthesis of single-crystal BaTiO 3 dendrites

In this paper, we report a simple hydrothermal method without any surfactants, for the first time, to synthesize single-crystal BaTiO 3 dendrites. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The KOH concentration was found to be vital to the final formation of BaTiO 3 dendrites. An obvious morphology evolution from sphere-like shape to dendrite was observed when KOH concentration was decreased from 1 M to 0.1 M. It is rational to expect that dendritic structures of other perovskite oxides may also be synthesized by this simple method.

Size effects on thin film ferroelectrics: Experiments on isolated single crystal sheets

Thin lamellae were cut from bulk single crystal BaTiO3 using a focused ion beam microscope. They were then removed and transferred onto single crystal MgO substrates, so that their functional properties could be measured independent of the original host bulk ferroelectric. The temperature dependence of the capacitance of these isolated single crystal films was found to be strongly bulklike, demonstrating a sharp Curie anomaly, as well as Curie–Weiss behavior. In addition, the sudden change in the remanent polarization as a function of temperature at TC was characteristic of a first order phase change. The work represents a dramatic improvement on that previously published by Saad et al. [J. Phys.: Condens. Matter 16, L451 (2004)], as critical shortcomings in the original specimen geometry, involving potential signal contributions from bulk BaTiO3, have now been obviated. That the functional properties of single crystal thin film lamellae are comparable to bulk, and not like those of conventionally deposited heterogeneous thin film systems, has therefore been confirmed.

Elastic softening and central peaks in BaTiO3 single crystals above the cubic-tetragonal phase-transition temperature

A strong relaxation mode was observed in the paraelectric phase of barium titanate (BaTiO3) single crystals by Brillouin scattering study and was found to correlate with the softening of the longitudinal acoustic mode and the increase in the hypersonic damping. These observations support the existence of polar percursors and their electrostrictive coupling with the strain caused by the acoustic waves, consistent with former studies evidencing off-centered Ti ions in the high-symmetry cubic phase. A critical slowing down has been clearly observed in the vicinity of the cubic-tetragonal phase transition, indicating order-disorder component contributes to the phase transition of BaTiO3.

Thermal conductivity of perovskite ferroelectrics

Thermal conductivities of BaTiO3, PbTiO3, KNbO3, KTaO3, NaNbO3, and Pb(Mg1∕3Nb2∕3)O3 (PMN) single crystals have been measured from 2to390K. Pronounced jumps are found at structural transitions in BaTiO3 and KNbO3. A low-temperature anomaly from soft optical phonons is observed in KTaO3. For PMN and NaNbO3, glasslike behavior is observed in both the thermal conductivity and heat capacity measurements. We associate the glasslike behavior in NaNbO3 with the phase separation phenomena reported in recent studies.

Crystal Growth and Ferroelectric Properties in Bi&lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt;–BaTiO&lt;sub&gt;3&lt;/sub&gt; Crystals

0.999Bi0.5Na0.5TiO3-0.001BaTiO3 (BNT-0.1%BT) single crystals with a maximum size of 1×1×1 mm3 were successfully grown by a flux method using BNT-6%BT powder and Bi2O3 as a flux. The crystals showed a remanent polarization of 33 μC/cm2 and coercive electric field of 40 kV/cm along [100]Cubic. Electric-field induced strain measurements along [100]Cubic revealed an effective piezoelectric strain constant d33 * of 80 pm/V.