Polycrystalline Barium Titanate Research Articles

Nanoimprinting Solution-Derived Barium Titanate for Electro-Optic Metasurfaces.

Electro-optic metasurfaces have demonstrated significant potential in enhancing the modulation speed and efficiency for fast and large-scale free-space optical devices. Barium titanate has a strong electro-optic Pockels coefficient, but its availability in thin-film form is restricted due to costly growth processes or low thickness. Here, we fabricated active metasurfaces using an etch-free bottom-up process with sol-gel-based polycrystalline barium titanate with a large electro-optic coefficient similar to bulk lithium niobate. We achieve strong hybrid Mie/surface lattice resonances with a quality-factor of 200 at 633 nm wavelength, enhancing the light-matter interaction and therefore the Pockels effect. The metasurface transmission is electro-optically modulated with up to 5 MHz driving frequency at low voltages of less than 1 V thanks to resonant enhancement of the modulation amplitude by 2 orders of magnitude. This successful demonstration of electro-optic modulation in nanoimprinted barium titanate structures paves the way for low-cost and large-scale free-space modulators or tunable metalenses.

Enhancing the Performance of 1–3 Lead-Free Piezoelectric Composites Using a CNT-Doped Matrix

This work presents a computational study on the impact of carbon nanotube (CNT) enriched matrix on the performance of 1–3 lead-free piezoelectric periodic composites. Specifically, we investigate a piezoelectric composite system consisting of [Formula: see text] parallel aligned fibers of polycrystalline barium titanate (BaTiO3) embedded in a polydimethylsiloxane (PDMS) matrix doped with multiwalled CNT. The effective properties and several figures of merit have been obtained to evaluate the performance of this composite system as is typically done for these materials used for sensing, actuating, or harvesting applications. The results reveal that, in lead-free BaTiO3/PDMS piezocomposites, the addition of CNTs in the PDMS matrix should be [Formula: see text] “being [Formula: see text] the percolation threshold”, but not higher. In another case, we will only improve the performance of the lead-free piezocomposite for sensing or actuating, but not for energy harvesting applications. This study provides insights into the use of multiwalled CNTs in lead-free piezocomposites and suggests the optimal concentration of CNTs to enhance their performance. The findings have potential implications for the development of new piezoelectric materials and devices for sensing and harvesting applications.

Temperature effect on elastic and fracture behaviour of lead-free piezoceramic BaTiO3

Ferroelectric ceramics, especially piezoceramics, are widely used in the field of sensors, micromanipulators, and capacitors. Barium titanate and its derivates are the first choices between lead-free materials. The main aim of the paper is to clarify fundamental processes taking place in the vicinity of Curie temperature with a focus on the fracture behaviour of pure polycrystalline barium titanate. The explanation of observed changes in the mechanical behaviour of this material is based on the experimental approach supported by numerical simulations utilising features of the real microstructure on the grain level. Several model materials with various grain microstructures were manufactured from the submicron barium titanate powder sintered at various temperatures. Two resulting materials with a suitable distribution of grains were selected for further investigation. The grain size influenced not only the exact position of the temperature of the Curie point but also the kinetics of the lattice transformation, elastic, and fracture properties. The significant drop observed in the fracture resistance was attributed to the development of localised internal thermal stresses, which was supported by the results of the performed numerical simulations. The coincidence of the volume change of neighbouring grains due to lattice transformation together with a significant variation in elastic properties can lead up to a 20% decrease in the measured fracture toughness. Understanding this behaviour is essential for the processing and correct application of lead-free barium titanate materials.

The negative dielectric permittivity of polycrystalline barium titanate nanofilms under high-strength kHz-AC fields

Unlike the conventional high-frequency dielectric behavior for which the amplitude of the applied field is too small to cause polarization switching, the dynamically-driven polarization reorientation brings remarkable frequency dependence to the nonlinear electromechanical behaviors of ferroelectric nanofilms. In this study, we developed a thermodynamically consistent phase-field model with an introduced second-order kinetic equation to investigate the dynamics of polarization switching in polycrystalline barium titanate nanofilms under high-strength AC fields. The newly introduced kinetic equation consists of an additional dynamic inertial term that brings about collective resonance of polarization within a certain frequency range. Negative dielectric permittivity is observed in a certain frequency band as the applied frequency varies from 30 to 80 kHz, and the maximum absolute value is reached around 40 kHz. It was demonstrated through microstructure-based analysis that such negative dielectric behavior is inherited from the frequency-dependent polarization switching in the nanograins. It also serves as the mechanism for other observed frequency-dependent physical properties, e.g., the remnant polarization, the piezoelectric coefficient at zero electric field and the coercive field. In addition, we further explored the influence of the damping coefficient in the kinetic equation and the influence of the in-plane strain to such frequency-dependent behaviors. It was found that a higher damping coefficient or applied in-plane strain tends to weaken the occurrence of negative permittivity.

Uncovering the symmetry of the induced ferroelectric phase transformation in polycrystalline barium titanate

Microstructural design is a widespread approach to tailor the properties of functional materials with the size effect being an effective constraint that modifies physical phenomena. In this work, we investigate the grain size effect on the properties and the electric field induced phase transformation behavior in barium titanate. A broad range of unimodal average grain size distribution between 0.4 and 15 μm was successfully sintered avoiding abnormal grain growth. Samples with a grain size close to the range of 1–2 μm, balancing microstructural strain, presence, and mobility of domain walls to allow the field induced crystal phase transformation, showed optimal electromechanical and dielectric properties. By means of in situ high energy x-ray diffraction and a high-resolution multianalyzer detector, we distinguish and quantify a tetragonal–orthorhombic phase transformation induced by an electric field, providing unambiguous proof of this induced phase transformation. These results contribute to the understanding of fundamental questions about the piezoelectric effect in barium titanate and consequently other similar systems.

In situ synthesis of TiO2@ BaTiO3 coaxial nanotubes coating on the titanium surface

Titanium dioxide nanotube coatings are prepared on the surface of titanium alloy to improve their biocompatibility, and the nanotube structure of the coating can be used for drug delivery. However, the titanium dioxide nanotube coating is an inert material, which still needs to be improved in terms of inducing bone growth. In this work, the TiO2 @ BaTiO3 coaxial nanotube coating on titanium surface was prepared by anodization combined with in-situ hydrothermal reaction. The nanotube structure was preserved in the TiO2 @ BaTiO3 coaxial nanotube coating, and the surface of the titanium dioxide nanotube was covered with polycrystalline barium titanate. Piezoelectric properties of the TiO2 @ BaTiO3 coaxial nanotube coating were clearly confirmed from the results of the amplitude and phase diagrams of the piezoelectric response which were tested by piezoelectric force microscopy. The TiO2 @ BaTiO3 coaxial nanotube coating on the surface of titanium alloy with piezoelectric properties and nanotube structure can be used for fast repair of bone defects and drug delivery.

Electromechanical Properties of Robocasted Barium Titanate Ceramics

This work presents the fabrication of dense polycrystalline barium titanate (BaTiO3, BT) for electromechanical transduction using robocasting and cold isostatic pressing (CIP). The use of CIP as post‐treatment is proposed to eliminate defects and increase the density of robocasted parts to improve the piezoelectric performance. For robocasting, pastes containing 50 and 52 vol% are developed; the resulting green robocasted parts are CIPed at 100 and 150 MPa. Using this proposed technique, samples robocasted with BT52 and CIPed at 150 MPa display a relative density of ≈98%, comparable with reference polycrystalline samples. In addition, an increase in both the piezoelectric charge and voltage coefficient is observed in robocasted parts, with the values up to 195 pC/N and 12 × 10−3 Vm N−1, respectively. These values, which are comparable with previous studies of polycrystalline BT, indicate that the combined robocasting and CIP technique is a possible method for producing 3D printed piezoelectric sensors.

High temperature creep‐mediated functionality in polycrystalline barium titanate

AbstractDislocations in oxides can be described as charged line defects and means for one‐dimensional doping, which can tune electrical and thermal properties. Furthermore, theoretically it was shown that dislocations can pin ferroelectric domain walls. Broader application of this concept hinges on the development of a methodology to avail this approach to polycrystalline ceramics. To this end, we use different creep mechanisms as a method to introduce multidimensional defects and quantify structural changes. A deformation map for fine‐grained barium titanate is provided and the influences of the defects and creep regimes are correlated in this first study to modifications of electrical conductivity, dielectric, ferroelectric, and piezoelectric properties. A plastic deformation of 1.29% resulted in an increase in the Curie temperature by 5°C and a decrease in electromechanical strain by 30%, pointing toward electromechanical hardening by dislocations.

Highly-transparent perovskite thin films obtained by a wet chemical processesing method

Barium titanate thin films are key materials for use in the solid-state devices, including capacitors, memories, thermistors, sensors, actuators and so on. High transmittance barium titanate thin films are suitable candidate for various electro-optic applications such as dielectric mirrors. In this research high transmittance barium titanate nanothin films were prepared by sol - gel dip - coating method, then the optical properties of the prepared nanofilms was characterized. Experimental results indicate that the surface morphology of prepared nanothin films were improved and as a result of that, a better optical properties, less optical losses were obtained in contrast with other reported data. It was found that optical propagation loss of barium titanate nanothin film was much lower than normal polycrystalline barium titanate thin film. Results also indicate that Increment of the calcination temperature reduces the thin films transparency and thickness. Other results show that increment of withdrawal rate of the substrate from the prepared sol lead to increment of thin films thickness and decrease in thin films transparency. The prepared high transparent nanothin film was amourphous and was as thin as 30 nm. It seems to us that, prepared barium titanate nanothin films would be suitable for several optical and electro-optical applications.

Multiferroic and magneto-dielectric properties in Fe doped BaTiO3

Polycrystalline barium titanate (BTO) samples doped with infinitesimal quantity of iron separately and simultaneously in both A and B sites are prepared using solid state reaction method with an emphasis on its site preference. Structural studies establish the transformation from tetragonal to pseudo-cubic phase upon changing the dopant site. An appreciable compressive lattice strain is induced when Fe is doped in the A-site while it becomes tensile and negligibly small when Fe occupies B-site. Further, the suppression of 308 cm−1 band in the Raman spectra highlights the coexisting cubic and tetragonal phases in A-site doped BTO. Ferroelectric ordering is validated using P–E loop and PUND (positive up and negative down) measurements. Dielectric constant undergoes a transition from ferroelectric to paraelectric state at 388 K for BTO and it varies with occupation site of Fe. Low temperature magnetic measurements reveal the strong antiferromagnetic coupling in A-site doped BTO sample. Magneto-dielectric measurements portray the proper choice of doping site in BaTiO3 so as to introduce multiple magnetic and electric states in it.

Ferroelectric domain evolution in gold nanoparticle-modified perovskite barium titanate ceramics by piezoresponse force microscopy

ABSTRACTThis work addresses the domain evolution processes in polycrystalline barium titanate (BaTiO3, BT)-based ceramics containing various amounts of gold nanoparticles (AuNPs) as an additive by using piezoresponse force microscopy (PFM). The obtained PFM images of the AuNPs-modified BT ceramics revealing the change of one spontaneously polarized state to another under various applied direct current (DC) voltage are discussed in terms of their domain topology, PFM phase shift and PFM amplitude. In general, complex microstructures containing almost round-shaped and micron-sized grains, and grain boundary regions are clearly seen in the topographic images of all samples. The obtained results point towards possibility of control the polarization switching of the AuNPs-modified BT ceramics with fined-grains sizes, by a selection of the proper applied DC voltage (VDC). The PFM investigation confirmed good dipole orientation within the AuNPs-modified BT ceramics containing submicron grain size at the elevated external fields and proved the lack of convenient domain switching of the unmodified BT case resulting from their larger grain size.

The anhysteretic polarisation of ferroelectrics

Measurement and calculation of anhysteretic curves is a well-established method in the field of magnetic materials and is applied to ferroelectric materials here. The anhysteretic curve is linked to a stable equilibrium state in the domain structure, and ignores dissipative effects related to mechanisms such as domain wall pinning. In this study, an experimental method for characterising the anhysteretic behaviour of ferroelectrics is presented, which is subsequently used to determine the anhysteretic polarisation response of polycrystalline barium titanate and a doped lead zirconate titanate composition at room temperature. Various external parameters, such as electric field, stress, and temperature, can significantly affect ferroelectric behaviour. Ferroelectric hysteresis curves can assess the importance of such effects but cannot distinguish their contribution on the different intrinsic and extrinsic mechanisms involved in ferroelectric behaviour. In this work, the influence of compressive stress on the anhysteretic polarisation is measured and discussed. The comparison of the polarization loop to the anhysteretic curve under compressive stress elucidates the effects on the stable equilibrium domain configuration and dynamic effects associated to dissipation.

Versatile Transfer of an Ultralong and Seamless Nanowire Array Crystallized at High Temperature for Use in High-Performance Flexible Devices.

Nanowire (NW) transfer technology has provided promising strategies to realize future flexible materials and electronics. Using this technology, geometrically controlled, high-quality NW arrays can now be obtained easily on various flexible substrates with high throughput. However, it is still challenging to extend this technology to a wide range of high-performance device applications because its limited temperature tolerance precludes the use of high-temperature annealing, which is essential for NW crystallization and functionalization. A pulsed laser technique has been developed to anneal NWs in the presence of a flexible substrate; however, the induced temperature is not high enough to improve the properties of materials such as ceramics and semiconductors. Here, we present a versatile nanotransfer method that is applicable to NWs that require high-temperature annealing. To successfully anneal NWs during their transfer, the developed fabrication method involves sequential removal of a nanoscale sacrificial layer. Using this method, we first produce an ultralong, perfectly aligned polycrystalline barium titanate (BaTiO3) NW array that is heat treated at 700 °C on a flexible polyethylene terephthalate (PET) substrate. This high-quality piezoelectric NW array on a flexible substrate is used as a flexible nanogenerator that generates current and voltage 37 and 10 times higher, respectively, than those of a nanogenerator made of noncrystallized BaTiO3 NWs.

Electromechanical Response of Polycrystalline Barium Titanate Resolved at the Grain Scale

Ferroic materials are critical components in many modern devices. Polycrystalline states of these materials dominate the market due to their cost effectiveness and ease of production. Studying the coupling of ferroic properties across grain boundaries and within clusters of grains is therefore critical for understanding bulk polycrystalline ferroic behavior. Here, three‐dimensional X‐ray diffraction is used to reconstruct a 3D grain map (grain orientations and neighborhoods) of a polycrystalline barium titanate sample and track the grain‐scale non‐180° ferroelectric domain switching strains of 139 individual grains in situ under an applied electric field. The map shows that each grain is located in a very unique local environment in terms of intergranular misorientations, leading to local strain heterogeneity in the as‐processed state of the sample. While primarily dependent on the crystallographic orientation relative to the field directions, the response of individual grains is also heterogeneous. These unique experimental results are of critical importance both when building the starting conditions and considering the validity of grain‐scale modeling efforts, and provide additional considerations in the design of novel ferroic materials.

Electric properties of polycrystalline (Ba1-xSrx)(Ti1-xZrx)O3 solid solution

ABSTRACTPolycrystalline samples of (Ba1-xSrx)(Ti1-xZrx)O3 (x = 0, 0.05, 0.10) were obtained by means of a conventional high temperature technology. SEM measurements show a well-formed structure with visible layers. The increase in Sr+2 and Zr+4 ions concentration reduces the temperature of paraelectric - ferrolectric phase transition and its diffusion increases. In the paraelectric state (for all samples) the Curie-Weiss law is fulfilled. From electric modulus measurements the relaxation times and the activation energy were determined. The investigation confirmed the improvement of the electrical properties compared with polycrystalline barium titanate.

Multilayer-WS2:ferroelectric composite for ultrafast tunable metamaterial-induced transparency applications

An ultrafast and low-power all-optical tunable metamaterial-induced transparency is realized, using polycrystalline barium titanate doped gold nanoparticles and multilayer tungsten disulfide microsheets as nonlinear optical materials. Large nonlinearity enhancement is obtained associated with quantum confinement effect, local-field effect, and reinforced interaction between light and multilayer tungsten disulfide. Low threshold pump intensity of 20 MW/cm2 is achieved. An ultrafast response time of 85 ps is maintained because of fast carrier relaxation dynamics in nanoscale crystal grains of polycrystalline barium titanate. This may be useful for the study of integrated photonic devices based on two-dimensional materials.

A novel mechanism to reduce coercive field of ferroelectric materials via {1 1 1} twin engineering

In the present work, we proposed a new strategy to increase the domain variants within the entire body of ferroelectrics, based on crystal twin engineering that increases the number of ferroelectric variants within each twinned grain, and demonstrated this strategy with polycrystalline barium titanate films. A novel thermomechanical treatment technique was developed to introduce {111} nanotwins into the films with different twin densities. The experimental results show that the coercive field is 32% lower in the high twin density samples than that in the low twin density ones. The conducted phase field simulations qualitatively confirmed the experimental results. Furthermore, the magnitude of the apparent saturation polarization is 72% higher in the high twin density samples than that in the low twin density samples. Twin engineering might be applied universally to all ferroelectric ceramics and films to substantially enhance their performance.

Low‐Temperature Control of Twins and Abnormal Grain Growth in BaTiO3

The microstructure of polycrystalline barium titanate (BaTiO3) thin films processed with a liquid‐phase can be controlled by the crystallographic orientation of the underlying sapphire substrate. During postdeposition crystallization, the tendency for {111} twin nucleation, which drives subsequent abnormal grain growth, depends upon the specific sapphire facet. Specifically, tilting away from the close‐packed c‐plane modifies the orientation, morphology, and relative amount of an interfacial BaAl2O4 second phase. These factors control the density of twin formation, and thus overall grain size of the crystallized BaTiO3. As the substrate orientation transitions from c‐plane, to r‐plane, to a‐plane, the twin density is reduced, the average grain size decreases systematically from 270 to 130 nm, and the grain structure becomes overall more homogeneous. This twinning mechanism and abnormal grain growth occur by 900°C, several hundred degrees lower than reported previously.

Influence of uniaxial stress on the ferroelectric-to-paraelectric phase change in barium titanate

The dielectric behavior near the ferroelectric-to-paraelectric phase transition of 〈001〉C-oriented single crystal and polycrystalline barium titanate (BaTiO3) was investigated as a function of uniaxial compressive stress in the temperature range from 25 to 200 °C. An increase in the Curie point (TC) and decrease in the Curie-Weiss temperature (θ) were observed with increasing stress for both single crystal and polycrystalline samples, resulting in an increase in the first order nature of the phase transition as measured by the temperature difference (TC – θ). With increasing applied stress levels, the permittivity versus temperature curves of polycrystalline samples were found to broaden and flatten near the Curie point, which was not observed for the single crystals. The experimental results were analyzed using a classical 2-4-6 Landau polynomial. The observed increase in the first order nature of the ferroelectric-to-paraelectric phase transition with uniaxial stress was explained by a linear dependence of the quartic coefficient of the Landau series on stress.

Critical mechanical and electrical transition behavior of BaTiO3: The observation of mechanical double loop behavior

Strain response of polycrystalline barium titanate (BaTiO3) was investigated under high unipolar electric field (0 to 4 kV/mm) and compressive stress (0 to 400 MPa) in the temperature range from 25 to 160 °C. In the vicinity of the Curie point (TC), nonlinear and hysteretic strain-electric field and strain-stress constitutive behaviors were observed, persisting above TC where they correspond to the well-known electric field induced double loop polarization behavior. Analogous to the electrical double loops, the mechanical (strain-stress) hysteretic behavior above TC is caused by a stress induced phase transition from the paraelectric/paraelastic to ferroelectric/ferroelastic phase; the electro-elastic (strain-electric field) hysteresis is similarly caused by an electric field induced phase transition. The stress and electric field at which transitions occur increase linearly with increasing temperature, exhibiting critical behavior typical for the first order phase transitions. The temperature limit for the induced phase transition extends up to 12 °C over TC. Results are discussed in relation to the Landau-Ginzburg-Devonshire free energy expansion.