Polydomain Phases Research Articles

Ferroelectricity in Ultrathin Halide Perovskites.

Ferroelectricity has recently been demonstrated in germanium-based halide perovskites. We use first-principles-based simulations to study 4-18 nm CsGeBr3 films and develop a theory for ferroelectric ultrathin films. The theory introduces (i) a local order parameter, which identifies phase transitions into both monodomain and polydomain phases, and (ii) a dipole pattern classifier, which allows efficient and reliable identification of dipole patterns. Application of the theory to both halides CsGeBr3 and CsGeI3 and oxide BiFeO3 ultrathin ferroelectrics reveals two distinct scenarios. First, the films transition into a monodomain phase below the critical value of the residual depolarizing field. Above this critical value, the second scenario occurs, and the film undergoes a transition into a nanodomain phase. The two scenarios exhibit opposite responses of Curie temperature to thickness reduction. Application of a dipole pattern classifier reveals rich nanodomain phases in halide films: nanostripes, labyrinths, zig-zags, pillars, and lego domains.

Phase patterning of liquid crystal elastomers by laser-induced dynamic crosslinking.

Liquid crystal elastomers hold promise in various fields due to their reversible transition of mechanical and optical properties across distinct phases. However, the lack of local phase patterning techniques and irreversible phase programming has hindered their broad implementation. Here we introduce laser-induced dynamic crosslinking, which leverages the precision and control offered by laser technology to achieve high-resolution multilevel patterning and transmittance modulation. Incorporation of allyl sulfide groups enables adaptive liquid crystal elastomers that can be reconfigured into desired phases or complex patterns. Laser-induced dynamic crosslinking is compatible with existing processing methods and allows the generation of thermo- and strain-responsive patterns that include isotropic, polydomain and monodomain phases within a single liquid crystal elastomer film. We show temporary information encryption at body temperature, expanding the functionality of liquid crystal elastomer devices in wearable applications.

Pressure effect on the formation kinetics of ferroelectric domain structure under first order phase transitions

Within the framework of Landau–Ginzburg theory the kinetics of domain structure formation in ferroelectrics that undergo first order phase transition was investigated under the influence of hydrostatic pressure. It was established that mechanical action increases the tendency of nonequilibrium system in the formation of stable polydomain structure. Numerical analysis showed that the process of domain ordering can proceed both directly and with formation of short-living metastable polydomain phase. It was found that the incubation period of domain structure formation can be observed at the initial stage of relaxation. Using the KNO3 crystal as an example, it was shown that the time of evolution of the system to the thermodynamic equilibrium is inversely proportional to the pressure value. It was established that in KDP crystals near phase transition point (TC–T < 10 K) the hydrostatic pressure induces the destruction of ferroelectric ordering. It was shown that the value of critical pressure pcr increases with the growth of quenching temperature.

Phase diagram and pyroelectric response of polydomain epitaxial Ba0.6Sr0.4TiO3 thin films

A nonlinear thermodynamic theory is used to investigate the phase structures, polarization and pyroelectric properties of polydomain epitaxial Ba0.6Sr0.4TiO3 thin films. Polydomain a1/a2/a1/a2, ca1/ca2/ca1/ca2, aa1/aa2/aa1/aa2, r1/r2/r1/r2 phases and single domain tetragonal c, paraelectric PE phases have been found in the misfit strain-temperature phase diagram. Note that the polydomain phases are found to be more complicated than single domain phases, which also leads to the variability of pyroelectric properties. The results of pyroelectric coefficients reveal that a distinguished in-plane and out-of-plane pyroelectric response appears near the phase boundaries of a1/a2/a1/a2-PE and ca1/ca2/ca1/ca2-c, c-PE, respectively, in which the pyroelectric coefficients |pi| are larger than 0.6 μC/cm2 K, exceeding most experimental and theoretical values. It is found that the maximum in-plane and out-of-plane pyroelectric coefficients occur under the strain of 0.23% and −0.225% at room temperature, respectively. The giant pyroelectric performance of polydomain Ba0.6Sr0.4TiO3 thin films may provide potential to highly sensitive infrared detectors.

Role of depolarization in the polarization reversal in ferroelectrics

Atomistic first-principles-based simulations are used to investigate polarization reversal in ferroelectrics in both the intrinsic and extrinsic regimes in order to determine the origin of nearly an order of magnitude difference in the coercive field predicted theoretically and observed in experiments. We find that the residual depolarizing field that is routinely ignored from considerations is responsible for the drastic reduction of the coercive field. The depolarizing field stabilizes a polydomain phase which allows for counterintuitive cooperation with the applied field to achieve polarization reversal in an energy-efficient way. Contrary to the common belief that low coercive field necessitates polarization reversal via domains formation and propagation, we predict that the same fields could be achieved if the residual depolarizing field is taken into account. An efficient way to incorporate such depolarizing field in any type of atomistic simulations is proposed, which is expected to resolve the longstanding issue of overestimation of fields in simulations of ferroelectrics.

Comparative study on heterophase structures in ferroelectric solid solutions based on barium titanate

Heterophase structures are first compared for related perovskite‐type ferroelectric solid solutions that are tin‐modified barium titanate and hafnium‐modified barium titanate with compositions near the morphotropic phase boundary. The studied heterophase structures are interpreted in terms of two models wherein two polydomain phases and a single‐domain interlayer or polydomain and single‐domain phases and a polydomain interlayer coexist at the complete stress relief. The role of the non‐180° domain types and unit‐cell parameters of the coexisting phases is highlighted to show the important link between the phase contents and unit‐cell parameters near the morphotropic phase boundary. A link between the heterophase/polydomain regions and piezoelectric activity of the ferroelectric solid solutions is discussed. Results on the phase contents in the morphotropic region are consistent with experimental data on the aforementioned solid solutions based on barium titanate.

Thermal conductivity of liquid crystalline epoxy/BN filler composites having ordered network structure

BN filler was added to a liquid crystalline (LC) epoxy resin to obtain a high thermal conductive material. The LC epoxy/BN composites, which were cured at different temperatures, formed an isotropic or LC polydomain phase structure. The relationship between the network orientation containing mesogenic groups and the dispersibility of the BN filler was discussed. As a result, the thermal conductivity of the LC polydomain system was drastically enhanced even at a relatively low volume fraction of BN (30vol%), regardless of the fact that both the LC and isotropic phase systems consisted of the same resin and filler content combination. This result is due to the formation of thermal conductive paths by the BN filler by exclusion of the BN filler from the LC domain formed during the curing process in the composite having the LC polydomain matrix.

Effect of misfit strain on the electrocaloric effect of polydomain epitaxial ferroelectric thin films

The effect of misfit strain on the electrocaloric effect in polydomain epitaxial BaTiO3 thin films at room temperature is investigated using the Ginzburg—Landau—Devonshire thermodynamic theory. Numerical calculations indicate that the misfit strain has a large impact on the ferroelectric polarization states and the electrocaloric effect. Most importantly, the electrocaloric effect in the polydomain ca1/ca2/ca1/ca2 phase is much larger than that in the monodomain c phase and the other polydomain phases. Consequently, a large electrocaloric effect can be obtained by carefully controlling the misfit strain, which may provide potential applications in refrigeration devices.

Pyroelectric properties of polydomain epitaxial Pb(Zr1−x,Tix)O3thin films

The pyroelectric properties of polydomain epitaxial Pb(Zr${}_{1\ensuremath{-}x}$,Ti${}_{x}$)O${}_{3}$ thin films are investigated using a Ginzburg--Landau--Devonshire thermodynamic model. We explore the three major contributions to pyroelectric response in thin films, including intrinsic effects and previously neglected contributions such as extrinsic and secondary effects, to provide a complete picture of pyroelectric property development. The pyroelectric coefficient for epitaxial thin films is calculated as a function of strain, temperature, and composition for 0.5 \ensuremath{\leqslant} $x$ \ensuremath{\leqslant} 1.0. We find that structural transitions driven by epitaxial strain can greatly enhance the pyroelectric coefficient and that extrinsic contributions due to temperature-driven domain wall motion can significantly alter the intrinsic pyroelectric properties. Furthermore, we show that the pyroelectric coefficient at room temperature is maximized at the multicritical point between various polydomain phases and is also consistently high along the boundary between the c/a/c/a and ${a}_{1}$/${a}_{2}$/${a}_{1}$/${a}_{2}$ polydomain phases. Additionally, we have investigated the impact of epitaxial strain on pyroelectric response in polydomain states and found that the extrinsic contribution from domain walls to the pyroelectric coefficient varies depending on the sign of the strain. Finally, we examine the addition of secondary contributions to pyroelectricity that arise from thermal expansion in materials and provide insight into the effect of this contribution on the overall magnitude of response.

Monoclinic phases and stress-relief conditions in (1 − x)Pb(Mg 1/3Nb 2/3)TiO 3– xPbTiO 3 solid solutions

A comparative study on heterophase states in perovskite-type solid solutions of (1 − x)Pb(Mg 1/3Nb 2/3)TiO 3– xPbTiO 3 is carried out for compositions near the morphotropic phase boundary. The conditions for mechanical stress relief at elastic matching of phases are analysed at x = const in a wide temperature range. The heterophase states concerned with the presence of the intermediate monoclinic phase are interpreted using the domain state–interface diagrams calculated for x = 0.28, 0.32 and 0.34. It is shown that optimum volume fraction parameters of the domains in the monoclinic phase of the B type are varied in relatively wide ranges and promote complete stress relief with cubic–monoclinic phase coexistence. Two scenarios of stress relief at x = 0.32 are considered in connection with different heterophase states (either tetragonal–monoclinic of the B type or tetragonal–monoclinic of the C type) in a wide temperature range. Possibilities of elastic matching of two polydomain phases (tetragonal–monoclinic of the B type) with almost equal relative widths of the domains in these phases are shown for x = 0.34. The active role of domains of the monoclinic phases in stress relief and forming the planar unstrained interfaces is discussed.

Correlation between non-180° domain structures in (1−x)PbA1∕3Nb2∕3O3−xPbTiO3 single crystals (A=Mg or Zn) under an applied [001] electric field

This work is devoted to the study of heterophase states in (1−x)PbA1∕3Nb2∕3O3−xPbTiO3 or PAN−xPT (A=Mg or Zn) single crystals under an electric field ‖E‖[001]. The possibility of elastically matched phases in the transformational sequences of Pm3m→P4mm→Cm, Pm3m→Cm, and P4mm→Cm are considered with regards to non-180° domains and changes in lattice parameters. Systems of diagrams linking domain types with interfaces between coexisting polydomain phases in PMN–0.28PT and PZN–0.045PT crystals are given. An important role of an intermediate P4mm phase in achieving stress accommodation has been identified by analysis of lattice parameters of PMN–0.28PT, and the elastic compatibility conditions between non-180° domain structures in the P4mm and Cm phases have been determined for various heterophase states. Two scenarios of changes in the lattice parameter aT in the P4mm phase of PMN–0.28PT have first been discussed to reveal possibilities of stress accommodation in heterophase states. It has been shown that the correlation between domain structures in different heterophase states of studied crystals stems from coordinated unit-cell behavior under ‖E‖[001].

Phase coexistence in [111] electric-field-cooled 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystals

Features of phase coexistence in polydomain0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystals cooled under an applied [111] electric fieldE have been investigated. A sequence of ferroelectric phases as well as the elastic matchingbetween coexisting phases in heterophase states has been analysed for cases where theangle between the spontaneous polarization vector of each domain type and the appliedE vector remains equal in each ferroelectric phase. This analysis is based on a method thatinvolves distortion matrices of the polydomain phases and invariants of interfaces regarded asquadric surfaces separating the phases. Results are represented in a system of diagrams linkingdomain states and interfaces at first-order phase transitions observed in [111] field-cooled0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystals. A ‘fine’ structure of the domain state–interface diagrams related totetragonal–orthorhombic phase coexistence has been revealed. It has been shown thatconditions for complete stress relaxation in different heterophase states are achieved for aphase sequence of tetragonal near single-domain orthorhombic single-domain monoclinic of the B type.

Links between polydomain phases in electric-field-cooled (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 single crystals

This letter is devoted to the analysis of interconnections between non-180° domain structures of ferroelectric phases in 0.70Pb(Mg1∕3Nb2∕3)O3–0.30PbTiO3 and 0.65Pb(Mg1∕3Nb2∕3)O3–0.35PbTiO3 single crystals cooled in the electric field E‖[001] or E‖[110]. Diagrams are proposed for the description of interfaces between the polydomain phases at various volume fractions of some domain types. Examples of the elastic matching of the polydomain phases along zero net strain planes are also considered.

Intermediate monoclinic phase and elastic matching in perovskite-type solid solutions

This paper is devoted to the study of elastic matching of phases coexisting in systems of perovskite-type solid solutions close to morphotropic phase boundaries. Determined are different interfaces that separate single-domain or polydomain phases in $(1\ensuremath{-}x){\mathrm{PbZn}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}\ensuremath{-}x{\mathrm{PbTiO}}_{3}$ single crystals and ${\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ ceramic grains. These interfaces are parallel to so-called zero net strain planes. Some results of recent experimental studies of the crystal structure and electromechanical properties are analyzed in connection with the revealed simplification of the domain structure in the intermediate monoclinic phase of $(1\ensuremath{-}x){\mathrm{PbZn}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}\ensuremath{-}x{\mathrm{PbTiO}}_{3}$ single crystals. The important role of the monoclinic phase in relieving stress at the phase coexistence in both the systems is considered. Links between optimal domain volume concentrations derived from unit-cell parameters' behavior are discussed on the basis of concepts of the polarization rotation path proposed by Fu and Cohen [Nature (London) 403, 281 (2000)].

Surface effects and ferroelectric phase transitions inBaTiO3ultrathin films

We present a finite-temperature study of ferroelectric phase transitions in ${\mathrm{BaTiO}}_{3}$ ultrathin films using an atomic-level simulation approach. This is based on a shell model for ${\mathrm{BaTiO}}_{3}$ with parameters obtained from first-principles calculations. While transitions involving in-plane electric polarization are practically unperturbed by the presence of the surface, surface atomic relaxations act as a strong perturbation on the ferroelectric order perpendicular to the surface. However, a strain induced ferroelectric polydomain phase with an out-of-plane orientation of polarization is stabilized in a not short-circuited film as thin as 20 \AA{}. A reduction of the out-of-plane polarization at the film surface is observed.

Interfaces in ferroelectrics and related materials with complex domain structures

This review is devoted to studies of polydomain and/or heterophase ferroelectric crystals containing different types of interfaces, i.e. domain walls, boundaries between polydomain regions or boundaries separating single- or polydomain phases.

Molecular relaxation in a photosensitive liquid-crystalline polymeric glass former

We have measured the relaxation to equilibrium in the supercooled nematic phase upon approach to of a fragile liquid-crystalline photosensitive polymeric glass former. Perturbation is introduced in a non-conventional way by optical pumping (orientation) of the nematic polydomain phase. Relaxation back to equilibrium is followed both on the microscopic scale, by means of depolarized time-resolved Raman experiments, and on the macroscopic scale, by means of quartz crystal microgravimetry.

Domain structures in bent In-22.5 at.%Tl polydomain crystals

The In-Tl alloy system was used to quantitatively study the deformation behavior of polydomain phases. Controlled twinned microstructures were prepared. It was found that the mesoscopic angle of rotation of domain-walls upon bending varies linearly with the applied strain, and quantitatively agrees with the theoretically derived prediction.

Mechanical stresses and three-phase states in perovskite-type ferroelectrics

Abstract A crystallographic theory has been proposed that takes into account an elastic matching of the polydomain (twinned) phases and allows to predict an evolution and interchange of three phases in perovskite-type ferroelectric single crystals. A diagram connecting these phases with the possible domain structures and their reconstruction has been discussed.

Polydomains in liquid‐crystal elastomers

AbstractIn liquid‐crystal elastomers, the simultaneous presence of rubber elasticity due to the crosslinked backbone chains and of optical birefringence due to the mesogens in the side chains lead to exceptional physical properties. An elastic deformation of the network influences the order of the mesogens and, therefore, the optical properties. A theory based on a Landau‐de Gennes expansion of the free energy is proposed. In the opaque polydomain phase, the local orientation is given by a compromise between the external mechanical field and a local anchoring interaction. As the field is increased, it becomes energetically favorable for the mesogens to align parallel to the mechanical field, and a transition to a transparent monodomain structure occurs. Results for the average orientation, the stress and the chain conformation are given.