Ferroelectric PbTiO3 Research Articles

Numerical investigation of nanoscale electromechanical response in a ferroelectric perovskite through an atomistic field theory

An atomistic field theory was introduced to study the electromechanical response in a ferroelectric perovskite at nanoscale. Based on a shell model potential, the polarization switching process of a ferroelectric perovskite PbTiO3 under electric field and mechanical loading was investigated. The simulation results showed that external electric field applied opposite to the initial polarization direction could result in 180° polarization switching in PbTiO3 nanostructures as the external electric field increased. On the other hand, mechanical loading applied parallel to initial polarization could cause 90° nanoscale polarization rotation in PbTiO3. Ultimately, the simulation results indicated that the coupled loads of electric field and mechanical loading would influence the polarization switching in PbTiO3 nanostructures.

Misfit strain relaxations of (101)-oriented ferroelectric PbTiO3/(La, Sr)(Al, Ta)O3thin film systems

Abstract

An Ultrathin Ferroelectric Perovskite Oxide Layer for High‐Performance Hole Transport Material Free Carbon Based Halide Perovskite Solar Cells

AbstractThe hole transport material (HTM) free carbon based perovskite solar cells (C‐PSCs) are promising for its manufactural simplicity, but they currently suffer from low power conversion efficiencies (PCE) largely because of the voltage loss. Here, a new strategy to increase the PCE by incorporating an ultrathin ferroelectric oxide PbTiO3 layer between the electron transport material and the halide perovskite is reported. The resulting C‐PSCs have achieved PCEs up to 16.37%, which is the highest record for HTM‐free C‐PSCs to date, mainly ascribable to the ferroelectric layer enhanced open circuit voltage. Detail measurements and analysis show an enhanced built‐in potential in the C‐PSCs as well as suppression of the non‐radiative recombination due to the ferroelectric PbTiO3 layer incorporation, accounting for the boosted VOC and photovoltaic performance.

Compression mechanisms of ferroelectric PbTiO3 via high pressure neutron scattering

Switchable atomic displacements generate electric dipole moments in ferroelectric materials utilized in many contemporary devices. Lead titanate, a perovskite oxide with formula PbTiO3, has been referred to as a textbook example of a prototype displacive ferroelectric and is a testing platform of widely used models of piezoelectric response of complex solid-solutions. PbTiO3 has been addressed by experimental and computational studies, often with apparently conflicting conclusions. To date, hydrostatic pressure experiments have been interpreted in terms of a model in which the dipole moments gradually diminish with increasing pressure until a transition to a cubic phase, characterized by a zero average dipole moment, occurs. The model unrealistically assumes an even compression of the crystal. Here we show by high-pressure neutron powder diffraction measurements that a fast and slow shrinkage of 12-oxygen cages around Pb and octahedra around Ti, respectively, takes place. A phase diagram consolidating earlier and present results is given.

Multistep coupling of preexisting local ferroic distortions in PbTiO3 above the Curie temperature

Temperature-dependent Raman spectroscopic analyses were performed for the prominent ferroelectric PbTiO3 in the temperature range 130–1040 K, focusing particularly on its paraelectric state above the Curie temperature K. The temperature evolution of the anomalous Raman scattering reveals that not only local ferroic distortions persist at temperatures well above , but also there is a sequence of different coupling processes preceding the appearance of long-range ferroelectric order at . Our results indicate that, similar to relaxor ferroelectrics, the paraelectric phase of PbTiO3 can be considered as an ergodic system of local ferroic distortions, which only on average appears to have cubic symmetry.

Polarization-induced selective growth of Au islands on single-domain ferroelectric PbTiO3 nanoplates with enhanced photocatalytic activity

In this work, heterostructured Au@PbTiO3 nanoplates were synthesized successfully via a simple hydrothermal process. It is revealed that Au islands with the size of 8–20 nm selectively deposited on the positively polarized surface of the single-crystal and single-domain PbTiO3 nonaplates. The composite demonstrates an efficient photocatalytic performance toward degradation of Rhodamine B (RhB) solution under UV light. The possible mechanism is that the ferroelectric polarization efficiently separates the photogenerated electrons and holes and reduces the recombination of them. Then, the ferroelectric polarization field urged the electrons concentrated on the positively polarized surface and then transformed oxygen into superoxide radicals to enhance the photocatalytic activity. Recycled activity tests show that the heterostructured Au@PbTiO3 nanoplates would inhibit the photocorrosion behavior and provide high stability.

Thermal conductivity of perovskite KTaO3 and PbTiO3 from first principles

The low thermal conductivity of piezoelectric perovskites is a challenge for high power transducer applications. We report first principles calculations of the thermal conductivity of ferroelectric PbTiO$_3$ and the cubic nearly ferroelectric perovskite KTaO$_3$. The calculated thermal conductivity of PbTiO$_3$ is much lower than that of KTaO$_3$ in accord with experiment. Analysis of the results shows that the reason for the low thermal conductivity of PbTiO$_3$ is the presence of low frequency optical phonons associated with the polar modes. These are less dispersive in PbTiO$_3$, leading to a large three phonon scattering phase space. These differences between the two materials are associated with the $A$-site driven ferroelectricity of PbTiO$_3$ in contrast to the $B$-site driven near ferroelectricity of KTaO$_3$. The results are discussed in the context of modification of the thermal conductivity of electroactive materials.

Na1/2Bi1/2VO3 and K1/2Bi1/2VO3: New Lead-Free Tetragonal Perovskites with Moderate c/a Ratios

New lead-free tetragonal perovskites Na1/2Bi1/2VO3 and K1/2Bi1/2VO3 were synthesized under high pressure (6 GPa) and high temperature (1473 K), based on the design of materials optimizing the lone pair effect of the A-site ion and utilizing the Jahn–Teller effect in the B-site V4+. The magnitudes of the c/a ratio and spontaneous polarization, PS, were 1.085 and 108 μC/cm2, respectively (73 μC/cm2 by the point charge model), for Na1/2Bi1/2VO3 and 1.054 and 92 μC/cm2, respectively (56 μC/cm2 by the point charge model), for K1/2Bi1/2VO3, which are comparable to the well-known lead-based ferroelectric PbTiO3. This approach can guide the design of new lead-free ferroelectric and piezoelectric materials.

Composite Ferroelectric and Plasmonic Particles for Hot Charge Separation and Photocatalytic Hydrogen Gas Production

Plasmonic nanoparticles are excellent light absorbers for harvesting solar energy, resulting in hot electrons that can be utilized in photocatalytic hydrogen production. However, the hot electrons generated in a localized surface plasmon resonance process have a very short lifetime and are challenging to use efficiently. Herein, using near IR light irradiation, we show that by combining gold nanorods (AuNRs) with ferroelectric PbTiO3 particles that possess a large remanent electric dipole moment, hot charges generated on plasmonic particles can be injected into ferroelectric materials and drive the photocatalysis reaction. Compared to metallic Pt-end-capped AuNRs, the efficiency of using hot electrons for photocatalytic reactions is enhanced for the composite catalyst, which improves the light-to-chemical energy conversion efficiencies by about 1 order of magnitude for the same amount of plasmonic particles being used.

Giant magnetoelectric effect at the graphone/ferroelectric interface

Multiferroic heterostructures combining ferromagnetic and ferroelectric layers are promising for applications in novel spintronic devices, such as memories with electrical writing and magnetic reading, assuming their magnetoelectric coupling (MEC) is strong enough. For conventional magnetic metal/ferroelectric heterostructures, however, the change of interfacial magnetic moment upon reversal of the electric polarization is often very weak. Here, by using first principles calculations, we demonstrate a new pathway towards a strong MEC at the interface between the semi-hydrogenated graphene (also called graphone) and ferroelectric PbTiO3. By reversing the polarization of PbTiO3, the magnetization of graphone can be electrically switched on and off through the change of carbon-oxygen bonding at the interface. Furthermore, a ferroelectric polarization can be preserved down to ultrathin PbTiO3 layers less than one nanometer due to an enhancement of the polarization at the interface. The predicted strong magnetoelectric effect in the ultimately thin graphone/ferroelectric layers opens a new opportunity for the electric control of magnetism in high-density devices.

Metastable vortex-like polarization textures in ferroelectric nanoparticles of different shapes and sizes

The dependence of the polarization texture topology in ferroelectric PbTiO3 nanoparticles, embedded in a dielectric matrix, on the particle shape and size was investigated with a time-dependent Landau-Ginzburg-Devonshire approach combined with coupled-physics finite-element-method based simulations. Particle shapes belonging to the superellipsoidal family were probed, including octahedral, cubic, and intermediate geometries. For each shape, a parametric sweep of particle sizes ranging from 2 to 40 nm was conducted, revealing a general trend for the texture transformations from a monodomain, through a vortex-like, to a multidomain state, as the size increases. Critical particle sizes for the texture instabilities were found to be strongly dependent on the particle shape, with octahedral particles undergoing transitions at much larger volumes, compared to the cubic particles. Furthermore, for each of the considered non-spherical shapes of appropriate size, it was possible to obtain multiple vortex-like textures whose paraelectric cores are aligned with every rotational axis of the particle point symmetry group. The shape-dependent metastability of the vortex-like textures opens up new avenues for controlling polarization at the nanoscale in a variety of technological applications.

EMI shielding properties of laminated graphene and PbTiO3 reinforced poly(3,4-ethylenedioxythiophene) nanocomposites

In this paper, PEDOT/reduced graphene oxide (RGO)/PbTiO3 nanocomposites have been synthesized using facile insitu chemical oxidative polymerization method. The synthesis method leads to the formation of core-shell structured nanocomposites containing PbTiO3 as primary filler and RGO as secondary filler in PEDOT matrix. The core-shell morphology of the composites has been confirmed using transmission electron microscope with average particle size 20–30 nm observed for PbTiO3. The incorporation of RGO and PbTiO3 in the PEDOT matrix has been confirmed by X-ray diffraction. A systematic study on electromagnetic shielding properties and the effect of PbTiO3 concentration on different properties has been carried out. The ferro-electric PbTiO3 with RGO induced dielectric loss in the composites, whereas, PEDOT establish a conducting network over RGO layer and PbTiO3 nanoparticles that improve electromagnetic shielding properties by increasing the dielectric loss. As a result, an enhanced electromagnetic shielding effectiveness value of 51.94 dB (>99.999% attenuation) has been achieved in 12.4–18 GHz frequency range. The nanocomposites were further characterized using Fourier transmission infrared spectroscopy and thermal gravimetric analysis.

The Polar/Antipolar Phase Boundary of BiMnO3–BiFeO3–PbTiO3: Interplay among Crystal Structure, Point Defects, and Multiferroism

AbstractThe ferromagnetic perovskite oxide BiMnO3 is a highly topical material, and the solid solutions it forms with antiferromagnetic/ferroelectric BiFeO3 and with ferroelectric PbTiO3 result in distinctive polar/nonpolar morphotropic phase boundaries (MPBs). The exploitation of such a type of MPBs could be a novel approach to engineer novel multiferroics with phase‐change magnetoelectric responses, in addition to ferroelectrics with enhanced electromechanical performance. Here, the interplay among crystal structure, point defects, and multiferroic properties of the BiMnO3–BiFeO3–PbTiO3 ternary system at its line of MPBs between polymorphs of tetragonal P4mm (polar) and orthorhombic Pnma (antipolar) symmetries is reported. A strong dependence of the phase coexistence on thermal history is found: phase percentage significantly changes whether the material is quenched or slowly cooled from high temperature. The origin of this phenomenon is investigated with temperature‐dependent structural and physical property characterizations. A major role of the complex defect chemistry, where a Bi/Pb‐deficiency allows Mn and Fe ions to have a mixed‐valence state, in the delicate balance between polymorphs is proposed, and its influence in the magnetic and electric ferroic orders is defined.

Determination of Ferro‐ and Antiferroelectricity Using the Temperature Dependence of the Pre‐Edge Features in the XANES Spectra: XANES Study of Tetragonal and Cubic ATiO3 (A = Sr, Ba, and Pb) and PbZrO3

The Ti and Zr K‐edge X‐ray absorption near edge structure (XANES) spectra of ATiO3 (A = Sr, Ba, and Pb) and PbZrO3 perovskite‐type compounds have been measured in the temperature range 20–900 K. Quantitative comparison is performed in a wide temperature range to clarify how the intensities of the pre‐edge peaks and shoulders change with temperature. In the ferro‐ and antiferroelectric tetragonal phases, the intensities of some of the peaks and shoulders decrease with increasing temperature and the peak‐top energies shift to the higher energy side. The shift can be explained by the position and decrease (increase for SrTiO3) of the D2 peak in the difference spectra. The peak‐top position of the pre‐edge peak in XANES does not always represent the true energy for independent transition to an orbital because several orbitals with similar energies overlap. The tetragonal SrTiO3 phase shows the same behavior as ferroelectric P4mm tetragonal BaTiO3 and PbTiO3 perovskite. The temperature dependence of the shoulder is also an important index. The presence of a phase with local polar tetragonal strain is important in materials and the Earth's constituent solid solutions. The existence of ferro‐ and antiferroelectricity can be determined by temperature‐dependent XANES measurements.

Mesopores induced zero thermal expansion in single-crystal ferroelectrics

For many decades, zero thermal expansion materials have been the focus of numerous investigations because of their intriguing physical properties and potential applications in high-precision instruments. Different strategies, such as composites, solid solution and doping, have been developed as promising approaches to obtain zero thermal expansion materials. However, microstructure controlled zero thermal expansion behavior via interface or surface has not been realized. Here we report the observation of an impressive zero thermal expansion (volumetric thermal expansion coefficient, −1.41 × 10−6 K−1, 293–623 K) in single-crystal ferroelectric PbTiO3 fibers with large-scale faceted and enclosed mesopores. The zero thermal expansion behavior is attributed to a synergetic effect of positive thermal expansion near the mesopores due to the oxygen-based polarization screening and negative thermal expansion from an intrinsic ferroelectricity. Our results show that a fascinating surface construction in negative thermal expansion ferroelectric materials could be a promising strategy to realize zero thermal expansion.

Electrical conduction on the surface of ferroelectric PbTiO3 thin film induced by electrolyte gating

We demonstrate a fairly high sheet conductance (∼1 μS) from 300 K to 10 K on the surface of ferroelectric PbTiO3 thin films in an electric double layer transistor configuration. Applying a positive gate voltage, n-type operation takes place with a high on-off ratio exceeding 105 and a high sheet electron density of 4 × 1013 cm−2. Temperature dependence of the sheet resistance changes from thermal activation-type at low gate voltage (∼3 V) to disordered two-dimensional conduction with a weak temperature dependence at high gate voltage (∼5 V). This behavior is quite different from those in BaTiO3 cases, where strong localization takes place below 100 K in electrostatically or chemically doped BaTiO3 thin films. The absence of instability to a lower symmetry crystal structure may play a role in the case of tetragonal PbTiO3.

Optical effects induced by epitaxial tension in lead titanate

Single-crystal-type epitaxial films of perovskite oxide ferroelectrics are attractive for integrated photonic applications because of the remarkable optical properties and effects in ferroelectrics. The properties of the films may be influenced by epitaxial strain arising from the film-substrate mismatch. Here, dramatic strain-induced changes of the absorption and refraction are experimentally detected by spectroscopic ellipsometry in epitaxial films of archetypical ferroelectric PbTiO3. Comparison of the properties of a tensile-strained film with those of reference films and crystals reveals that epitaxial tension produces blueshifts of the primary above-bandgap absorption peaks by 1 eV and a decrease in the refractive index by 0.5 in the transparent spectral range. The obtained quadratic electrooptic and effective elastooptic coefficients exceed the bulk values by orders of magnitude. The experimental observations prove that epitaxy is a powerful tool for engineering unprecedented optical properties that may enable future photonics innovations.

Polarization-dependent epitaxial growth and photocatalytic performance of ferroelectric oxide heterostructures

Epitaxial heterostructures are of particular interest owing to their fascinating properties for wide applications in energy, environment and electronic devices. The understanding of epitaxial growth in solution phase, however, remains a fundamental challenge to realize the rational synthesis of heterostructures. Here we report that anatase TiO2 can epitaxially grow on the selective polar surface of single-crystal and single-domain ferroelectric PbTiO3 nanoplates. The interplay of ferroelectric polar surface and corresponding ion adsorptions on them has been revealed experimentally and theoretically to determine the epitaxial growth mode, giving rising to zero-dimensional (0D)/two-dimensional (2D) and 2D/2D heterostructures. A combination of experimental and theoretical calculations indicate that the resulting heterostructures adopt a polarization-dependent photocatalytic performance under visible light irradiation, including hole-based photodegradation and electron-based hydrogen evolution reaction (HER) of water splitting. Such findings allow investigation of the potential of ferroelectric polarization towards tuning epitaxial growth and functionality of heterostructures.

Phase-field modeling and electronic structural analysis of flexoelectric effect at 180° domain walls in ferroelectric PbTiO3

The flexoelectric effect is the coupling between strain, polarization, and their gradients, which are prominent at the nanoscale. Although this effect is important to understand nanostructures, such as domain walls in ferroelectrics, its electronic mechanism is not clear. In this work, we combined phase-field simulations and first-principles calculations to study the 180° domain walls in tetragonal ferroelectric PbTiO3 and found that the source of Néel components is the gradient of the square of spontaneous polarization. Electronic structural analysis reveals that there is a redistribution of electronic charge density and potential around domain walls, which produces the electric field and Néel components. This work thus sheds light on the electronic mechanism of the flexoelectric effect around 180° domain walls in tetragonal ferroelectrics.

Unusual soft mode dynamics in ferroelectric PbTiO3 nanowire under different mechanical boundary conditions

First-principles-based atomistic simulations are used to investigate equilibrium phases and soft mode dynamics in ultrathin ferroelectric PbTiO3 nanowire with poor surface charge compensation subjected to a wide range of mechanical boundary conditions. The presence of the depolarizing field along the nanowire's transverse directions leads to the appearance of a unique high-frequency hard phonon mode that can be used to characterize electrical boundary conditions. This mode is insensitive to the mechanical load. Hydrostatic pressure was found to significantly influence the Curie point and ferroelectric soft modes in the nanowire. Uniaxial stress applied either along axial or transverse nanowire's direction is capable of inducing polydomain flux-closure phases that have a unique “dynamical” fingerprint. In such phases, the modes that originate from the soft modes of bulk PbTiO3 become hard, which could open a way to potential identification of such nanodomain phases. In all cases, uniaxial stress significantly increases the Curie temperature.