Ferroelectric Inclusion Research Articles

Lead-Free Ferroelectric Ba0.9Sr0.1TiO3 Coupled Polysulfide Trapping on Sulfur Cathode in Stable and High Energy Density Lithium-Sulfur (Li-S) Batteries

In the present work we are reporting electrochemical performance of Lead-free ferroelectric Ba0.9 Sr0.1TiO3 (BST), a high polarization (~14.58 μC/cm2 ) material, to assist polysulfide chemisorption via their permanent dipoles. The performance of fabricated cathodes in terms of structural, electronic, morphological, and electrochemical characteristics have been carried out with various concentrations of ferroelectric inclusion. X-ray diffraction analysis revealed tetragonal symmetry (c/a=1.0073) and the Raman spectroscopic studies confirmed A1(TO1), A1(TO2), A1(TO3) and A1(LO3) optical modes of the tetragonal phase of the BST modified composites. All the compositional cations were observed in SEM-based EDAX analysis, confirming homogeneous distribution of BST in the sulfur cathode system having grain sizes of ~ 1-1.5 μm. The porosity in the composites were found to be negligible based on the microscopic analysis. Considering that polar substances have good affinity towards trapping polysulfides and that can provide more stable reacting environment in the cathodic site, ferroelectric BST was employed to trap such polysulfide intermediates due to possessing permanent dielectric polarizability. With the spontaneous polarization induced by composite structure, ferroelectric material provides internal electric fields and increase chemisorption with the reactive heteropolar material. Thus, BST coupled C-S composite cathodes improved the electrochemical performance in comparison with the cathodes composed of only C-S. A stable high capacity of 1200 mAh/g was achieved for the BST coupled C-S cathodes in contrast to 700 mAh/g in pristine C-S cathode, due to reduction in polysulfides migration influence by the electric field of the BST ferroelectric. Two plateaus were observed, namely at 1.5 V and 3 V in the charge/discharge characteristics. The detail results will be presented at the ECS meeting 2023.

Size, shape, and orientation dependence of the field-induced behavior in ferroelectric nanoparticles

Ferroelectric-dielectric composite materials are attractive for a range of applications in future functional devices. Here, we utilized a free energy based computational approach to investigate the electric-field driven response of isolated ferroelectric nanoparticles embedded in a dielectric matrix and its dependence on particle size, shape, and orientation of the applied field E. Particle shapes belonging to the superellipsoidal family were considered, including octahedral, spherical, and cuboidal structures, as well as a number of intermediate geometries. Perovskite PbTiO3 and SrTiO3, respectively, were chosen as the prototypical ferroelectric and dielectric materials. In particles of all shapes that are large enough to support domain walls at zero applied field, we observed polarization switching by a formation of intermediate phases, which possess an appreciable amount of vorticity stemming from the domain wall motion through the ferroelectric inclusion volume. The system coercive field Ec and energy storage efficiency were found to be strongly dependent on the particle shape and the orientation, but not on its size. In near spherical particles with easy polarization axis pointing away from the direction of E, smallest Ec and highest storage efficiencies were obtained, while nonspherical particles with aligned easy polarization and E directions exhibited highest Ec and relatively low energy storage efficiencies.

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites.

The temperature of the transition to the polar state in ferroelectric composites, representing spherical ferroelectric inclusions embedded in a dielectric matrix, under a depolarizing field effect is investigated. This temperature is determined both in the absence and presence of screening effects of the depolarizing field of the bound charges of spontaneous polarization at the inclusions surface. The absence case shows that the Curie point shift is determined by the ratio of the Curie constant of the ferroelectric inclusion to the permittivity of the matrix. Screening effects show that the transition temperature shift decreases through multiplying the value by a decreasing factor equal to the ratio of the screening length to the radius of the ferroelectric inclusion. Examples of the materials for the position of the Curie point on the temperature scale, largely determined by the tilting action of the depolarizing field and the compensating shielding effects, are given.

Phase diagrams of ferroelectric nanocrystals strained by an elastic matrix

Ferroelectric crystallites embedded into a dielectric matrix experience temperature-dependent elastic strains caused by differences in the thermal expansion of the crystallites and the matrix. Owing to the electrostriction, these lattice strains may affect polarization states of ferroelectric inclusions significantly, making them different from those of a stress-free bulk crystal. Here, using a nonlinear thermodynamic theory, we study the mechanical effect of elastic matrix on the phase states of embedded single-domain ferroelectric nanocrystals. Their equilibrium polarization states are determined by minimizing a special thermodynamic potential that describes the energetics of an ellipsoidal ferroelectric inclusion surrounded by a linear elastic medium. To demonstrate the stability ranges of such states for a given material combination, we construct a phase diagram, where the inclusion’s shape anisotropy and temperature are used as two parameters. The ‘shape-temperature’ phase diagrams are calculated numerically for PbTiO3 and BaTiO3 nanocrystals embedded into representative dielectric matrices generating tensile (silica glass) or compressive (potassium silicate glass) thermal stresses inside ferroelectric inclusions. The developed phase maps demonstrate that the joint effect of thermal stresses and matrix-induced elastic clamping of ferroelectric inclusions gives rise to several important features in the polarization behavior of PbTiO3 and BaTiO3 nanocrystals. In particular, the Curie temperature displays a nonmonotonic variation with the ellipsoid’s aspect ratio, being minimal for spherical inclusions. Furthermore, the diagrams show that the polarization orientation with respect to the ellipsoid’s symmetry axis is controlled by the shape anisotropy and the sign of thermal stresses. Under certain conditions, the mechanical inclusion-matrix interaction qualitatively alters the evolution of ferroelectric states on cooling, inducing a structural transition in PbTiO3 nanocrystals and suppressing in BaTiO3 inclusions some transformations occurring in their bulk counterpart. The constructed phase maps open the possibility to calculate dielectric properties of strained PbTiO3 and BaTiO3 nanocrystals and ferroelectric nanocomposites comprising such crystallites.

Inorganic Anions Regulate the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules

Inorganic Anions Regulate the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules

Polarization states and dielectric responses of elastically clamped ferroelectric nanocrystals

Polarization states and physical properties of ferroelectrics depend on the mechanical boundary conditions due to electrostrictive coupling between electric polarization and lattice strains. Here, we describe theoretically both equilibrium thermodynamic states and electric permittivities of ferroelectric nanocrystals subjected to the elastic three-dimensional (3D) clamping by a surrounding dielectric material. The problem is solved by the minimization of a special thermodynamic potential that describes the case of an ellipsoidal ferroelectric inclusion embedded into a linear elastic matrix. Numerical calculations are performed for BaTiO3, PbTiO3, and Pb(Zr0.5Ti0.5)O3 nanoparticles surrounded by silica glass. It is shown that, in the case of BaTiO3 and PbTiO3, elastic 3D clamping may change the order of a ferroelectric phase transition from first to second. Furthermore, the mechanical inclusion–matrix interaction shifts the temperatures of structural transitions between different ferroelectric states and even eliminates some ferroelectric phases existing in stress-free BaTiO3 and Pb(Zr0.5Ti0.5)O3 crystals. Another important effect of elastic clamping is the lowering of the symmetry of ferroelectric states in ellipsoidal inclusions, where orthorhombic and monoclinic phases may form instead of the tetragonal and rhombohedral bulk counterparts. Finally, our thermodynamic calculations show that the dielectric responses of studied perovskite ferroelectrics are sensitive to matrix-induced clamping as well. For instance, dielectric peaks occurring at structural transitions between different ferroelectric phases in BaTiO3 appear to be much higher in spherical inclusions than in the freestanding crystal. Predicted clamping-induced enhancement of certain dielectric responses at room temperature indicates that composite materials comprising nanocrystals of perovskite ferroelectrics are promising for device applications requiring the use of high-permittivity dielectrics.

Dielectric responses of composite films based on P(VDF-TrFE) copolymer with TGS inclusions

The dielectric characteristics of film samples of P(VDF-TrFE) + TGS composite in the frequency range of 103–107 Hz are studied. The values of the real and imaginary parts of the complex dielectric constant in the temperature range of–40 to 140°C, including the points of the polymer matrix’s transition to the glassy state when Tg ≈–25°C and the ferroelectric phase transition. An analysis of the ferroelectric crystal inclusion effect on the dielectric response of P(VDF-TrFE) copolymer matrix is carried out.

On the change in the mechanism of the phase transition in a ferroelectric inclusion of a ferroelectric-dielectric nanocomposite as a function of its size

It has been shown using the numerical analysis of the nonlinear system of equations that the phase transition in a ferroelectric inclusion, starting from a specific size depending on its shape, occurs into an inhomogeneous “domain-like” state. The structure of this state and the temperature region of its existence have been investigated. Possibilities of the experimental manifestation of the inhomogeneous state have been discussed. In particular, the specific features of the permittivity of such systems have been analyzed in detail.

Dielectric properties of porous aluminum and silicon oxides with inclusions of triglycine sulfate and its modified analogs

This paper reports on an investigation of the temperature dependences of the capacitance and conductance of composite materials prepared by incorporating the ferroelectric TGS and its analogs—TGS with addition of L,α-alanine and chromium—into porous Al2O3 and SiO2 matrices. It has been established that conduction of the structures under study involves charge transport predominantly through the ferroelectric embedded in the porous matrix. A mechanism is proposed to account for the displacement of the phase transition temperature of the ferroelectric inclusion under “restricted geometry” conditions, which is driven by the difference between the thermal expansion coefficients of the porous matrix and the embedded ferroelectric.

The p–T phase diagram for new ferroelectric bis-thiourea pyridinium bromide

The effects of temperature and pressure on physical properties of the ferroelectric inclusion compound bis-thiourea pyridinium bromide were studied by dielectric spectroscopy, neutron and X-ray diffractometry and nuclear magnetic resonance (NMR). The results permitted a construction of the p–T phase diagram for this compound. At ambient pressure bis-thiourea pyridinium bromide exists in three phases and the ferro-ferroelectric phase transition observed at T2=150K is discontinuous in contrast to the ferro-paraelectric phase transition observed at T1=180K. The application of pressure of about 800MPa at room temperature and then cooling of this compound to below T=160K induces the appearance of a new phase (IV).

Redetermination of the structure and dielectric properties of bis(thiourea) pyridinium iodide – a new ferroelectric inclusion compound

The crystal structure of bis(thiourea) pyridinium iodide (T(2)PyI) was previously determined at 295 and 110 K [Prout, Heyes, Dobson, McDaid, Maris, Mueller & Seaman (2000). Chem. Mater. 12, 3561-3569] and the two phases were described in the space groups Cmcm and P2(1)cn, respectively. Because differential scanning calorimetry revealed two phase transitions, at 161 and 141 K, a redetermination of the structure of T(2)pyI at 295, 155 and 110 K has been undertaken, and the following sequence of space groups obtained: Cmcm (I) --> C2cm (II) --> P2(1)cn (III). The high- (I) and low-temperature (III) phases confirmed the results reported in the previous study. In the new intermediate phase II, the mirror plane perpendicular to the x axis vanishes and the crystal structure loses the centre of symmetry. In phases I and II the pyridinium cations are strongly dynamically disordered, while in the low-temperature phase III the cations are well ordered. In all three phases the thiourea-iodine hydrogen-bonded sublattice is very well ordered. Dielectric measurements show that the intermediate and low-temperature phases are ferroelectric and that 161 K is the Curie point of a new ferroelectric crystal.

An Interpretation of Ferroelectric Crystal Ageing

By SEM and TEM of film replicae a lot of virgin and aged (electrical and thermal fatigues) of different ferroelectric families are studied. We conclude that the ageing proccess is caused by the growth of ferroelectric crystalline inclusion.

On the problem of the ferroelectric inclusion in a matrix subjected to pressure

The energy of formation of a ferroelectric phase in an inhomogeneous inclusion, forming part of a composite system, is shown to be determined by the energy balance within, and, in reference to, the composite system as a whole. Eshelby's theory of the elastic inhomogeneity is applied to obtain the elastic strain energy as a result of temperature variations, phase change, and externally applied pressure. The dependence of the dielectric properties on temperature and pressure is related to the permittivity variations and to changes in screening of the local field intensity through changes in the depolarization factors.