BaTiO3 Thin Films Research Articles

High-Temperature Energy Storage Properties of Bi0.5Na0.5TiO3-0.06BaTiO3 Thin Films

Bi0.5Na0.5TiO3-0.06BaTiO3 (BNT-BT) thin films were prepared via both chemical solution (CSD) and pulsed laser deposition (PLD). The structural, dielectric, and ferroelectric properties were investigated. High stability of the dielectric permittivity or TCC (∆ε/ε (150 °C) ≤ ±15%) over a wide temperature range from room temperature to 300 °C was obtained. Distinctly, the CSD film showed high TCC stability with variation of ±5% up to 250 °C. Furthermore, the CSD film showed an unsaturated ferroelectric hysteresis loop characteristic of the ergodic relaxor phase. However, the PLD one exhibited an almost saturated loop characteristic of the coexistence of both ergodic and non-ergodic states. The energy storage properties of the prepared films were determined using P–E loops obtained at different temperatures. The results show that these films exhibited a stable and improved energy storage density comparable to ceramic capacitors. Moreover, the CSD film exhibited more rigidity and better energy storage density, which exceeded 1.3 J/cm3 under a weak applied field of 317 kV/cm, as well as interesting efficiency in a large temperature range. The obtained results are very promising for energy storage capacitors operating at high temperatures.

Optimization of power conversion efficiency of BaTiO3 as a compact layer in DSSC using response surface methodology/Box-Behnken design

This study focused on the optimization of BaTiO3 thin film as a compact layer in a dye-sensitized solar cell (DSSC) by spin-coating method. The experiment was designed using response surface methodology with Box-Behnken design (RSM/BBD). Three key parameters were studied i.e., annealing time, annealing temperature and the number of drop-casting. Three independent variables and three levels were used in the experiment involving 17 experiments to analyse the optimum deposition condition. The interaction between these factors was studied and used to identify the best parameters to improve the DSSC performance. The statistical analysis showed that the three parameters studied significantly affected the power conversion efficiency (PCE). After optimization of parameters, a specific optimum deposition condition, A = 3 h (annealing duration), B = 485 °C (annealing temperature) and C = 3 (number of drop-casting) was obtained. According to the optimum condition, the predicted PCE value was 4.87%. A validation experiment was carried out and a PCE of 4.92 ± 0.04% was achieved, which is in good agreement with the predicted result.

Lead-free ferroelectric BaTİO3 (BTO) thin films produced by the green process

In this study, we present structural and dielectric properties of doped and un-doped BaTiO3 (BTO) thin films samples. BTO sample were produced by non-vacuum process specifically sol-gel spin coating technique. The doped samples involve Co, Gd, Mn, Sr, and Zr in the Ba-site of the BTO. We used SEM, XRD and AFM analysis techniques to characterized our samples. We also conduct a dielectric measurement using a Vector Network Analyzer. According to our findings the highest dielectric constants were observed for Sr and Zr doped BaTiO3 thin films which were not applied any heat treatment and were obtained as 9.25 and 9.4 ​at 5.4 ​GHz frequency, respectively. On the other hand, the value of dielectric constants of the films that were analyzed after heat treatment were determined as 7.7 and 7.45 ​at 6.8 ​GHz on Sr and Zr doped BaTiO3 thin films, respectively.

Control of resistive switching type in BaTiO3 thin films grown by high and low laser fluence

A ferroelectric memristor has attracted much attention due to convenient controlling by polarization switching, but the resistive switching has been attributed to the drift or charge trapping of defects. To distinguish the resistive switching mechanism between ferroelectric polarization switching and the normal resistive switching mechanism such as the drift or charge trapping of defects, BaTiO3 (BTO) thin films were grown on a (001) Nb:SrTiO3 single crystal substrate by pulsed laser deposition with high and low laser energy density. Based on a piezoelectric force microscope, ferroelectricity is found in BTO thin films grown at high laser energy density. X-ray photoelectron spectroscopy further confirms the existence of defects in the BTO films grown at low laser energy density. The high energy sample with low density of defects exhibits a resistance hysteresis loop but little current hysteresis loop, while the low energy sample with high density of defects shows a significant resistance and current hysteresis loop simultaneously. These results provide a deep understanding about the resistive switching from ferroelectric polarization switching and the drift or charge trapping of defects.

Effect of aging on microstructural and optical properties of sol-gel dip coated BaTiO3 thin films

This paper reports the effect of aging, thickness, and annealing temperature on microstructural and optical properties of sol-gel dip-coated BaTiO3 (BTO) thin films. The absence of any sharp peaks in the XRD pattern confirmed the amorphous nature of thin films regardless of the aging time of the solution and the thickness. Annealed BTO thin films showed the polycrystalline structure of films, which indicated the formation of a single-phase compound, and increased the intensity with respect to the annealing temperature from 550 to 650 °C. The crystallite size of annealed films increased from 19.44 nm to 23.6 nm, while the lattice strain and dislocation density decreased from 6.63 × 10−3 to 5.65 × 10−3 and 2.65 × 1011 to 1.79 × 1011 cm−2 as the annealing temperature increased from 550 to 650 °C, respectively. The bandgap of as-deposited (solution aged from 48 - 96 h) films decreased from 3.90 to 3.87 eV, while the bandgap of annealed films increased from 3.19 to 3.86 eV as the annealing temperature increased from 550 to 650 °C owing to releasing the defects of films. The near band edge emission (NBE) of all annealed samples was observed to be 361 nm which is in close agreement with the estimated bandgap. The variation of aging, thickness, and annealing temperature of BTO thin films can significantly improve the physical properties of optoelectronic applications.

Optical investigation and computational modelling of BaTiO3 for optoelectronic devices applications

ABX3 perovskite-based materials have attracted research attention in various electronic and optoelectronic applications. The ability to tune the energy band gap through various dopants makes perovskites a potential candidate in many implementations. Among various perovskite materials, BaTiO3 has shown great applicability as a robust UV absorber with an energy band gap of around 3.2 eV. Herein, we provide a new sonochemical-assisted solid-phase method for preparing BaTiO3 thin films that optoelectronic devices can typically be used. BaTiO3 nano-powder and the thin film deposited on a glass substrate were characterized using physicochemical and optical techniques. In addition, the work demonstrated a computational attempt to optically model the BaTiO3 from the atomistic level using density functional theory to the thin film level using finite difference time domain Maxwell's equation solver. Seeking repeatability, the dispersion and the extinction behavior of the BaTiO3 thin film have been modeled using Lorentz-Dude (LD) coefficients, where all fitting parameters are listed. A numerical model has been experimentally verified using the experimental UV–Vis spectrometer measurements, recording an average root-mean-square error of 1.44%.

Stoichiometric Control and Optical Properties of BaTiO3 Thin Films Grown by Hybrid MBE

AbstractBaTiO3 is a technologically relevant material in the perovskite oxide class with above‐room‐temperature ferroelectricity and a very large electro‐optical coefficient, making it highly suitable for emerging electronic and photonic devices. An easy, robust, straightforward, and scalable growth method is required to synthesize epitaxial BaTiO3 thin films with sufficient control over the film's stoichiometry to achieve reproducible thin film properties. Here the growth of BaTiO3 thin films by hybrid molecular beam epitaxy is reported. A self‐regulated growth window is identified using complementary information obtained from reflection high energy electron diffraction, the intrinsic film lattice parameter, film surface morphology, and scanning transmission electron microscopy. Subsequent optical characterization of the BaTiO3 films by spectroscopic ellipsometry revealed refractive index and extinction coefficient values closely resembling those of stoichiometric bulk BaTiO3 crystals for films grown inside the growth window. Even in the absence of a lattice parameter change of BaTiO3 thin films, degradation of optical properties is observed, accompanied by the appearance of a wide optical absorption peak in the IR spectrum, attributed to optical transitions involving defect states present. Therefore, the optical properties of BaTiO3 can be utilized as a much finer and more straightforward probe to determine the stoichiometry level present in BaTiO3 films.

Strained BaTiO3 thin films via in-situ crystallization using atomic layer deposition on SrTiO3 substrate

The interface engineering of oxide heterostructures, such as BaTiO3 (BTO)/SrTiO3 (STO), has received considerable attention because of their interesting physical/electrical properties. In this study, the in-situ crystallization of BTO thin film was achieved using a high temperature (∼350 °C) atomic layer deposition (ALD) process, which enabled the formation of strained BTO thin films on the STO substrate. A compressive strain was introduced along the in-plane direction of the BTO film, resulting in a 1.5% decrease in the lattice constant of BTO film while an in-plane tensile strain was induced in the STO layer (0.8% increase in the lattice constant). The in-situ crystallization of BTO thin films grown by ALD allowed the formation of a strained interface at the BTO/STO heterostructure.

Polarization-dependent electrocaloric and pyroelectric effects in ferroelectric BaTiO3 thin films

Herein, we examine the influence of controllable polarization reversal and built-in electric fields on pyroelectric and electrocaloric effects in a BaTiO3 thin film using a modified indirect method. We find that the magnitude of the sample's change in polarization with temperature is sensitive to the degree of polarization reversal. The pyroelectric response is small at low fractions of switched polarization and grows larger by several factors as larger fractions of polarization are reversed. This polarization reversal-sensitive pyroelectric behavior is the result of an internal built-in field, which has the effect of destabilizing low fractions of switched polarization and producing diminished pyroelectric effect. Greater fractions of switched polarization are more stable against backswitching and permit a larger pyroelectric response. Our findings highlight a characterization method for polarization-dependent pyroelectric effects in ferroelectric thin films, where built-in field effects are also present.

Nanoscale Surface Structure of Nanometer-Thick Ferroelectric BaTiO3 Films Revealed by Synchrotron X-ray Scanning Tunneling Microscopy: Implications for Catalytic Adsorption Reactions

Ferroelectric nanomaterials are of interest in catalysis, nonvolatile memory, and neuromorphic computing among other applications because of their switchable structure that can alter the electronic and interface properties of a single material. The investigation of the role of polarization on the surface structure and chemistry of ferroelectric nanomaterials is a longstanding challenge, as it ideally requires a combination of both nanoscale imaging and chemical spectroscopy. In this work, we study a model ferroelectric BaTiO3 thin film by synchrotron X-ray scanning tunneling microscopy (SX-STM), a unique method that integrates nanoscale surface imaging and chemically sensitive spectroscopy. We find that polarization switching from downward to upward in (001) single-crystalline BaTiO3 thin films increases the intensity of X-ray absorption across Ba M, Ti L, and O K edges. Chemical mapping of nanometer-sized domains further demonstrates the modulation of surface structures upon polarization switching, as well as confirming the trends observed in single-point experiments across the surface. We complement these measurements with ab initio computational absorption spectroscopy to elucidate the effect of polarization switching on the core–hole excitations using the Bethe–Salpeter equation approach. Our experimental and theoretical results thus confirm a stronger binding strength for the upward-polarized surface with molecular O2 as a model reactant, offering mechanistic evidence that supports previous reports. This work advances the understanding of the surface chemistry and electronic structure of ferroelectrics, which can ultimately aid strategies to design interfaces with tailored properties.

Sn-modified BaTiO3 thin film with enhanced polarization

Hybrid molecular beam epitaxy (MBE) growth of Sn-modified BaTiO3 films was realized with varying domain structures and crystal symmetries across the entire composition space. Macroscopic and microscopic structures and the crystal symmetry of these thin films were determined using a combination of optical second harmonic generation (SHG) polarimetry and scanning transmission electron microscopy (STEM). SHG polarimetry revealed a variation in the global crystal symmetry of the films from tetragonal (P4mm) to cubic (Pm3¯m) across the composition range, x = 0 to 1 in BaTi1−xSnxO3 (BTSO). STEM imaging shows that the long-range polar order observed when the Sn content is low (x = 0.09) transformed to a short-range polar order as the Sn content increased (x = 0.48). Consistent with atomic displacement measurements from STEM, the largest polarization was obtained at the lowest Sn content of x = 0.09 in Sn-modified BaTiO3 as determined by SHG. These results agree with recent bulk ceramic reports and further identify this material system as a potential replacement for Pb-containing relaxor-based thin film devices.

Plasma etching and surface characteristics depending on the crystallinity of the BaTiO3 thin film

Due to its high dielectric constant (κ), the BaTiO3 (BTO) thin film has significant potential as a next-generation dielectric material for metal oxide semiconductor field-effect transistors (MOSFETs). Hence, the evaluation of the BTO thin film etching process is required for such nanoscale device applications. Herein, the etching characteristics and surface properties are examined according to the crystallinity of the BTO thin film. The results demonstrate that the etching rate is low in the high-crystallinity thin film, and the surface residues are much lower than in the low-crystallinity thin film. In particular, the accelerated Cl radicals in the plasma are shown to penetrate more easily into the low-crystallinity thin film than the high-crystallinity thin film. After the etching process, the surface roughness is significantly lower in the high-crystallinity thin film than in the low-crystallinity thin film. This result is expected to provide useful information for the process design of high-performance electronic devices.

Characterization of electro-optic coefficients r13, r23 and r33 in single crystalline BaTiO3 thin films

We report experimental characterization of DC electro-optic coefficients r13, r23 and r33 in thin film single crystalline BaTiO3 on DyScO3. The epitaxial BaTiO3 thin film is sandwiched between a SrRuO3 bottom electrode and an indium tin oxide (ITO) top electrode. We characterize the DC electro-optic coefficients r13, r23, and r33 by the prism coupling method at 636.6 nm for the BaTiO3 thin film. The results show the DC coefficients r13 = 4.2 pm/V, r23 = 4.6 pm/V and r33 = 9.0 pm/V.

Effects of Sn doping on piezoelectric power generation and energy density of flexible BaTiO3 thin films

Ferroelectric thin films find applications in numerous areas, including sensors and energy storage devices. To address the toxicity associated with thin films such as Pb(Zr,Ti)O3, developing Pb-free ferroelectric thin films with enhanced physical properties is necessary. Herein, the piezoelectric power generation and energy density of Sn-doped BaTiO3 (SBTO) thin films with varying Sn doping concentrations were studied. Polycrystalline SBTO thin films with Sn doping concentrations of 0%, 5%, 10%, and 15% were deposited on flexible Pt/mica substrates with a preferential (111) orientation. The SBTO thin film with a Sn doping concentration of 5% exhibited the highest remanent polarization (Pr) in the ferroelectric hysteresis loop. In contrast, the SBTO thin films with Sn doping concentrations of 10% and 15% exhibited reduced Pr owing to the formation of 90° domains. The lowest Pr was observed for the SBTO thin film with 15% Sn. With an increase in the Sn doping concentration, the piezoelectric coefficient (d33) increased due to the formation of a-domains. Owing to the high concentration of a domain, the SBTO thin film with 15% Sn exhibited the highest d33 and consequently, the highest piezoelectric power generation voltage. Moreover, the minimum Pr of the film with 15% Sn facilitated an increase in energy density and efficiency.

Disentangling electronic and thermal contributions to light-induced resistance switching in BaTiO3 ferroelectric tunnel junction

In the presence of asymmetric potential barriers, such as those created by imprint fields, ferroelectric polarization can be reversed by light due to the photoinduced suppression of polarization. Both thermal effects and photocarrier-induced polarization screening may agree with this experimental observation, challenging its understanding. Here, we explore light-induced ferroelectric polarization switching in BaTiO3 thin films. Time-dependent photocurrent and photoresistance experiments at different wavelengths indicate that the optical switch of polarization is mainly driven by photocarriers rather than thermal effects. The effect of light on sample polarization is found to be relatively slow and that an illumination period as long as ≈100 s is required to achieve complete switching when using a 405 nm light wavelength and 1.4 W/cm2 power density. It is shown that this response is governed by the concentration of photo-generated charges, which is low due to the reduced light absorption of BaTiO3 films at the explored wavelengths. Our conclusions can help us to better design optically switching devices based on ferroelectric materials.

Evolution of epitaxial BaTiO3 on SrTiO3-buffered Si: Phase field analysis

Barium titanate (BaTiO3) is a promising candidate for electro-optical modulators in Si photonics. The BaTiO3 ferroelectric domain morphology is strongly affected by thermal, electrical, and mechanical conditions and, in turn, profoundly influences the film's optical properties. Because BaTiO3 film growth takes place at a relatively high temperature, upon cooling, the film is subject to complex thermal effects that involve changes in the crystal phase, the emergence of ferroelectricity, and variations in the strain level. We use a phase field model to describe the evolution of the BaTiO3 thin film domain morphology upon cooling from growth to room temperature. We demonstrate that cooling under different cooling scenarios results in different domain morphologies. Our simulations provide a clear temperature–strain map and thermal strategy for controllable BaTiO3 epitaxy on the SrTiO3-buffered Si substrate.

Bio-synapse behavior controlled by interface engineering in ferroelectric tunnel memristors

The interface engineering is always an important way to modulate the behavior of the ferroelectric tunnel memristor (FTM), which directly affects its biological synaptic properties. Here, to investigate the effect of interface on bio-synapse performance, FTMs with the structure of Pt/ BaTiO3/La0.67Sr0.33MnO3 were studied, of which the interfaces of the device can be controlled through tailoring the termination of the SrTiO3 substrate and the unit-cell of BaTiO3 thin film by its growth mode. FTMs with different interfaces present opposite resistive switching behaviors due to the contrary polarization directions and the different band alignments in the BaTiO3 film. More importantly, the synaptic learning properties of FTMs can also be tuned by tailoring the interface. FTMs with different interface terminations could modulate different properties of long-term potentiation (LTP), long-term depression (LTD), spike-timing-dependent plasticity (STDP), and paired-pulse facilitation (PPF). Based on the synaptic behaviors of these two interface-engineered FTMs, the artificial neural network (ANN) system could be constructed to complete a handwritten digital image recognition process, and the accuracies of both are close to 90%. Our results provide a useful reference for tuning the functionalities of memristors through nanoscale interface engineering.

Temperature tunable electromagnetically induced transparency in terahertz metasurface fabricated on ferroelectric platform

The integration of active materials in terahertz (THz) metasurfaces is pivotal for the realization of functional device applications in diverse fields like sensing, imaging, communication, etc. In this context, ferroelectric materials endowed with tunable electro-optic properties have recently emerged as a novel candidate for achieving actively tuned THz metasurfaces. Here, we experimentally investigate temperature tuning of electromagnetically induced transparency (EIT) effects in a THz metasurface based on ferroelectric barium titanate (BaTiO3 (BTO)) thin film. We characterize tunable dielectric properties of the BTO thin film under variable temperatures (25 °C–100 °C) at THz frequencies by utilizing THz-time domain spectroscopy technique. Based on this aspect, we design a THz metasurface capable of displaying the EIT effect. THz transmissions through the metasurface sample are then probed for different applied temperatures. The EIT features undergo frequency shifts along with amplitude modulations owing to the temperature induced variations of the dielectric properties of the BTO thin film. A total red shift ∼27 GHz in EIT resonance dip is observed experimentally as the temperature increases from 25 °C to 100 °C. Therefore, we demonstrate utilities of ferroelectric platform toward the development of temperature tunable EIT metasurfaces.

Optical study of a-BaTiO3 thin films grown at different annealing temperatures

Thin films of amorphous BaTiO3 (a-BTO) were grown by spin coating technique on a glass substrate and annealed at different temperatures, from 300 to 500 °C, with a step of 50 °C. The samples were characterized structurally by X-ray diffraction (XRD), where broadband around 25° indicates the amorphous formation in all the thin films. The optical properties of the a-BTO thin films were determined by transmittance and reflectance UV-Visible spectroscopy. The optical responses were fit using Lorentz and Lorentz-Tauc classical models to determine the complex dielectric function. In addition, the photoluminescence (PL) of the glass and the a-BTO/glass system was also measured to observe the antireflective capacity of the a-BTO thin film as a function of the calcination temperature. To understand the experimental structural results ab-initio molecular dynamic calculation of 2x2x2 BTO supercell was utilized, while the electronic density of state and the complex dielectric function were obtained using Density Functional Theory (DFT). A comparison between the experimental and theoretical results is presented and discussed.

Microstructures and Optical Properties of Nanocrystalline Pr- doped BaTiO3 Thin Film

Microstructures and Optical Properties of Nanocrystalline Pr- doped BaTiO3 Thin Film