Domain Orientation Distribution Research Articles

Domain Interactions Determine the Conformational Ensemble of the Periplasmic Chaperone Sura

SurA is thought to be the most important periplasmic chaperone for outer membrane protein (OMP) biogenesis. Its structure is composed of a core region and two peptidylprolyl isomerase domains, termed P1 and P2, connected by flexible linkers. As such these three independent folding units are able to adopt a number of distinct spatial positions with respect to each other. The conformational dynamics of these domains are thought to be functionally important yet are largely unresolved. Here we address this question of the conformational ensemble using sedimentation equilibrium, small-angle neutron scattering, and folding titrations. This combination of orthogonal methods converges on a SurA population that is monomeric at physiological concentrations. The conformation that dominates this population has the P1 and core domains docked to one another, for example, "P1-closed" and the P2 domain extended in solution. We discovered that the distribution of domain orientations is defined by modest and favorable interactions between the core domain and either the P1 or the P2 domains. These two peptidylprolyl domains compete with each other for core-binding but are thermodynamically uncoupled. This arrangement implies two novel insights. Firstly, an open conformation must exist to facilitate P1 and P2 exchange on the core, indicating that the open client-binding conformation is populated at low levels even in the absence of client unfolded OMPs. Secondly, competition between P1 and P2 binding paradoxically occludes the client binding site on the core, which may serve to preserve the reservoir of binding-competent apo-SurA in the periplasm.

Domain interactions determine the conformational ensemble of the periplasmic chaperone SurA.

SurA is thought to be the most important periplasmic chaperone for outer membrane protein (OMP) biogenesis. Its structure is composed of a core region and two peptidylprolyl isomerase domains, termed P1 and P2, connected by flexible linkers. As such these three independent folding units are able to adopt a number of distinct spatial positions with respect to each other. The conformational dynamics of these domains are thought to be functionally important yet are largely unresolved. Here we address this question of the conformational ensemble using sedimentation equilibrium, small-angle neutron scattering, and folding titrations. This combination of orthogonal methods converges on a SurA population that is monomeric at physiological concentrations. The conformation that dominates this population has the P1 and core domains docked to one another, for example, "P1-closed" and the P2 domain extended in solution. We discovered that the distribution of domain orientations is defined by modest and favorable interactions between the core domain and either the P1 or the P2 domains. These two peptidylprolyl domains compete with each other for core-binding but are thermodynamically uncoupled. This arrangement implies two novel insights. Firstly, an open conformation must exist to facilitate P1 and P2 exchange on the core, indicating that the open client-binding conformation is populated at low levels even in the absence of client unfolded OMPs. Secondly, competition between P1 and P2 binding paradoxically occludes the client binding site on the core, which may serve to preserve the reservoir of binding-competent apo-SurA in the periplasm.

Micromechanical simulation of ferroelectric domain processes at crack tips

The electromechanical loading situation at cracks in ferroelectric ceramics is essentially affected by domain switching. Under high electrical and/or mechanical external fields, the state of polarization and remanent strains is substantially changed at the crack tip. These irreversible dissipative processes influence the fracture toughness of the cracked ferroelectric material. In the present paper, the micromechanical domain switching processes at the crack tip are studied by numerical simulation and compared with the in situ experimental results obtained by Jones et al. (Acta Mater 55(16):5538–5548, 2007) using X-ray diffraction analyses in synchrotron. Main attention is payed to the spatial distribution of preferred domain orientation in a mechanically loaded compact tension specimen made of a soft tetragonal lead zirconate titanate ceramics. It is found that the mechanically induced favored domain orientation distribution depends on position within the plane of the CT specimen and correlates with projected deviatoric stresses and strains. Some issues concerning shortcomings in the experimental and simulation results are raised and discussed. The outcome of this type of simulations forms the basis for more realistic fracture mechanical evaluations in future.

Reconstruction of the domain orientation distribution function of polycrystalline PZT ceramics using vector piezoresponse force microscopy

Lead zirconate titanate (PZT) is one of the prominent materials used in polycrystalline piezoelectric devices. Since the ferroelectric domain orientation is the most important parameter affecting the electromechanical performance, analyzing the domain orientation distribution is of great importance for the development and understanding of improved piezoceramic devices. Here, vector piezoresponse force microscopy (vector-PFM) has been applied in order to reconstruct the ferroelectric domain orientation distribution function of polished sections of device-ready polycrystalline lead zirconate titanate (PZT) material. A measurement procedure and a computer program based on the software Mathematica have been developed to automatically evaluate the vector-PFM data for reconstructing the domain orientation function. The method is tested on differently in-plane and out-of-plane poled PZT samples, and the results reveal the expected domain patterns and allow determination of the polarization orientation distribution function at high accuracy.

Influence of ferroelectric domain texture on the performance of multilayer piezoelectric actuators

Lead zirconate titanate (PZT)-based multilayer piezoelectric actuators (MAs) present a maximum in their piezoelectric properties when pre-stressed with a low mechanical load (ca. 50MPa) along the longitudinal axis of the actuator. In this work, we investigate this phenomenon by combining polarised Raman spectroscopy with a Reverse Monte Carlo (RMC) method in order to quantify the domain orientation distribution of PZT-based MAs, both in-situ and at the remanent state, under combined applied electric field and mechanical load. Our study shows that the performance maximum of MAs is the result of two competing effects: (i) an increasing reservoir for non-180° domain switching for increasing applied compressive pre-stress and (ii) a large activation energy for domain switching at high pre-stresses. Hence, our study uncovers structure-property relationships in piezoceramic components that could be used to finely tune the electromechanical response of actuators.

Modelling of hysteretic behavior of piezoceramic materials under electrical loading

The purpose of this study is to model the hysteretic behavior of piezoceramic materials under electrical loading. Remanent strain and remanent polarization are chosen as internal variables. A domain orientation distribution is used to describe the evolution of these variables by bridging the characteristics of microscopic domain distribution into macroscopic behaviors. This model is able to calculate electric displacement, longitudinal, and transversal strains as a function of uniaxial electrical field. Good quality of the formulation is demonstrated through comparison with experimental data of the literature. In addition, results confirm our hypothesis of isochoric deformation of piezoceramics under electrical loading.

Micromechanical estimate of the elastic properties of the coherent domains in pyrolytic carbon

On the nanoscale, the microstructure of pyrolytic carbon (PyC) is constituted by an ensemble of graphene planes, which manifest themselves as lattice fringes in high-resolution transmission electron microscope images. This microstructure can be also considered by an aggregate of so-called coherent domains consisting of stacks of graphene planes with a common unit normal vector. In order to homogenize the elastic behavior of PyC on the micro-level, image processing techniques are used to detect the coherent domains. Subsequently, the domain orientation distribution function (DODF) is modeled by means of a von Mises-Fisher distribution. The main objective of the present paper is to estimate the elastic properties of the coherent domains of the PyC microstructure. Moreover, the Hashin-Shtrikman bounds for the elastic properties can be determined by taking into account the DODF and by applying a nonlinear averaging procedure of the spatially dependent deviations of the local elastic properties. The elastic properties of the coherent domains are estimated by an inverse parameter identification of the Hashin-Shtrikman homogenization method by using effective elastic properties. The latter ones have been obtained based on an Fourier-based image processing algorithm and the orientation distribution function of the graphene planes in a recent paper (Bohlke et al. in Z Angew Math Mech, 2012).

Modelling of hysteretic behaviour of piezoceramic materials under external electrical and mechanical stress

The purpose of this study is to model the non-linear hysteretic behaviour of piezoceramic materials under an external (mechanical or electrical) stress. The model is constructed by bridging the characteristics of microscopic domain distribution into the macroscopic behaviour. Choosing the remanent strain and remanent polarisation as internal variables, a domain orientation distribution is used to describe the evolution of these variables and to develop a phenomenological model of ferroelasticity for electromechanical loading histories. This model is able to reproduce the (longitudinal and transversal) strain and electric displacement in function of uniaxial electrical and mechanical loading. This formulation is validated through a comparison with experimental data of the literature. The evolution of the elastic and piezoelectric constants under mechanical stress is successfully compared as well.

Estimate of the Domain Orientation Distribution Function and the Thermoelastic Properties of Pyrolytic Carbon Based on an Image Processing Technique

AbstractThe microstructure of Pyrolytic Carbon (PyC) can be described as an aggregate of coherent domains with different orientations. The domains exhibit an approximately a hexagonal material symmetry. In order to apply statistical homogenization schemes which predict the thermomechanical properties in terms of the microstructural characteristics, a quantitative description of PyC microstructures based on the domain orientation distribution function (DODF) is introduced in this work. The von‐Mises Fisher distribution is applied for modeling the orientation of the unit normal vectors of the graphene planes. The respective probabilty density function depends on the so‐called concentration parameter κ. The parameter κ is estimated by the set of domain orientations, which can be obtained by applying the image processing technique. This procedure facilitates the estimate of the 2nd order bounds (Hashin‐Shtrikman upper and lower bounds) based on the real microstructure. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Quantitative analysis of domain texture in polycrystalline barium titanate by polarized Raman microprobe spectroscopy

A quantitative determination of domain distribution in polycrystalline barium titanate (BaTiO3, henceforth BT) ceramics has been pursued with the aid of a microprobe polarized Raman spectrometer. The crystallographic texture and domain orientation distribution of BT ceramics, which switched upon applying stress according to ferroelasticity principles, were determined from the relative intensity of selected phonon modes, taking into consideration a theoretical analysis of the angular dependence of phonon mode intensity for the tetragonal BT phase. Furthermore, the angular dependence of Raman intensity measured in polycrystalline BT depended on the statistical distribution of domain angles in the laser microprobe, which was explicitly taken into account in this work for obtaining a quantitative analysis of domain orientation for in-plane textured BT polycrystalline materials.

Crack tip process zone domain switching in a soft lead zirconate titanate ceramic

Non-180° domain switching leads to fracture toughness enhancement in ferroelastic materials. Using a high-energy synchrotron X-ray source and a two-dimensional detector in transmission geometry, non-180° domain switching and crystallographic lattice strains were measured in situ around a crack tip in a soft tetragonal lead zirconate titanate ceramic. At K I = 0.71 MPa m 1/2 and below the initiation toughness, the process zone size, spatial distribution of preferred domain orientations, and lattice strains near the crack tip are a strong function of direction within the plane of the compact tension specimen. Deviatoric stresses and strains calculated using a finite element model and projected to the same directions measured in diffraction correlate with the measured spatial distributions and directional dependencies. Some preferred orientations remain in the crack wake after the crack has propagated; within the crack wake, the tetragonal 0 0 1 axis has a preferred orientation both perpendicular to the crack face and toward the crack front.

Neutron reflectivity investigations of EuS/PbS superlattices grown on (1 1 1) BaF 2 substrate

The existence of the pronounced ferromagnetic interlayer correlations in EuS/PbS superlattices grown in the [1 1 1] direction on BaF 2 substrate has been revealed by unpolarized neutron reflectivity measurements. This is in a stark contrast with the previous findings of antiferromagnetic interlayer coupling in a similar EuS/PbS superlattices grown in the [0 0 1] direction on KCl substrate. In order to confirm that the observed FM correlations result from interlayer exchange coupling, rather than from spurious layer magnetization alignment, the in-plane magnetic domain orientation distribution has been investigated with neutron polarization analysis.

A domain evolution model for hysteresis in piezoceramic materials

In this paper, we use a circular distribution to quantify certain domain properties and model the hysteresis behavior of piezoceramic materials. The model is constructed by bridging the characteristics of microscopic domain distribution into the macroscopic (or bulk) behavior. Contributions, other than those associated with the polarization of domains, to bulk quantities are also counted. A domain orientation distribution function is first selected and the corresponding distribution function parameters are chosen as the internal state variables. For the two-dimensional model, a von Mises-Fisher circular distribution is used. Instead of micromechanical analysis of domain motions that would involve large computation efforts, the delineation of domain evolution is simplified by considering the evolution of the domain orientation distribution, which is determined by the dynamic variations of the internal state variables. We also develop a procedure to identify the material constants introduced in the constitutive equations. The models are used to quantitatively characterize various hysteresis loops observed in piezoceramic materials.

Polar magneto-optical Kerr effect for low-symmetric ferromagnets

The polar magneto-optical Kerr effect (MOKE) for low-symmetric ferromagnetic crystals is investigated theoretically based on first-principle calculations of optical conductivities and a transfer matrix approach for the electrodynamics part of the problem. Exact average magneto-optical properties of polycrystals are described, taking into account realistic models for the distribution of domain orientations. It is shown that for low-symmetric ferromagnetic single crystals the MOKE is determined by an interplay of crystallographic birefringence and magnetic effects. Calculations for single and bi-crystal of hcp 11-20 Co and for a polycrystal of CrO_2 are performed, with results being in good agreement with experimental data.

An analytical axisymmetric model for the poling-history dependent behavior of ferroelectricceramics

The poling-history dependent behavior of ferroelectric ceramics has beeninvestigated by experimental tests. A suddenly poled ferroelectric ceramic wasfound to have significantly larger remnant polarization and strain than thecorresponding values of a gradually poled one. To explain this phenomenon, a newdomain-switching criterion for ferroelectric ceramics is proposed, in which each180° switching is dividedinto two successive 90° switchings. In a suddenly poled ceramic, the strong intergranular interaction after the first90° switching is favorable for accomplishing the second90° switching. The effects of poling-dependent effects are then taken intoaccount by evaluating different levels of energy dissipation after the first90° switching. The domain orientation distribution function (ODF) as well as the macroscopicpolarization and strain are analytically derived under cyclic electric loading. In thenon-dissipation case, the macroscopic polarization of a ferroelectric ceramic can be ideallysaturated as long as the magnitude of the applied electric field exceeds (EC is the coercive field), while in the full dissipation case, the maximum macroscopicpolarization is related to the magnitude of the applied electric field. The hysteresis loopsfor the non-dissipation case are almost identical to the corresponding loops of asuddenly poled ceramic, and the hysteresis loops for the full dissipation case arevery close to those of a gradually poled ceramic. The good agreement betweenthe analytical and experimental results indicates the validity of the proposedmodel in describing the poling-history dependent effects in ferroelectric ceramics.

Investigation of magnetization reversal in FeCoV/Ti multilayers

We report on the influence of different sputtering conditions on the structural and magnetic properties of FeCoV/Ti multilayers. A combination of magnetically soft and hard layers, separated by nonmagnetic Ti layers, is realized. A series of multilayers with varying Ti layer thicknesses is prepared at different deposition conditions compared to identical samples from a previous series in order to study the influence of preparation conditions on the magnetization reversal process. Intense Bragg peaks in the specular X-ray reflectivity indicate smooth interfaces. There is no pronounced dependence of the coercivity of individual FeCoV layers on Ti thickness. Polarized neutron reflectivity (PNR) is performed at selected positions of the hysteresis loop in order to obtain a layer resolved magnetization profile. Modelling the magnetization profile, to meet the experimental data, give a reduced magnetization parallel to the applied magnetic field. This indicates a multi-domain state of the FeCoV layers with a distribution of individual domain orientations depending on the external field.

Comparison of the Kerr effect and X-ray pole figure methods for determining crystallographic texture in PrFeB magnets

In this study, magnetic domains in Pr16Fe76B8 sintered magnets have been observed by Kerr effect and a histogram of the angular distribution of domain orientations has been used to determine the magnetic texture (〈cosΦ〉). The degree of easy-axis alignment of Pr2Fe14B matrix grains in these magnets has been also determined by X-ray pole figure analysis using the (004) reflection. The (004) pole figure measurements were carried out by the Schultz's reflection method. The (004) normalized intensity data has been fitted for a Gaussian distribution and the degree of crystal alignment, 〈cosΘ〉, has been calculated using the Stoner–Wohlfarth model. Comparison of these methods has been carried out. It has been shown that in magnets with medium and high degrees of crystallographic alignment, the pole figure values are higher than that obtained by the Kerr effect method. Conversely, in magnets with low degrees of alignment, 〈cosΘ〉 is lower than 〈cosΦ〉.

Modeling of electric field induced texture in lead zirconate titanate ceramics

Preferred domain orientation of a piezoelectric ceramic develops through domain switching under electric poling. In previous investigations the critical free energy required for domain switching has been assumed as a constant. This assumption leads to overestimation of the poling-induced texture and provides no explanation for the switching reversal in ferroelectric ceramics after the poling field is removed. In this paper, the contribution of intergranular stress to critical energy for 90° domain switching is investigated. A criterion including intrinsic threshold energy and an interaction energy, which is related to the intergranular stress and the intergranular depolarization field, is proposed. The texture evolution during poling process is simulated using a computational model starting from an initial random domain orientation distribution. The resulted domain orientation distributions under and after poling are predicted. The remanent domain switching after poling is the result of the balance between the interaction energy and intrinsic threshold energy. The final texture is much weaker than that under the electric field. Pole figures of poled Navy VI lead zirconate titanate measured by x-ray diffraction are consistent with the predicted textures.

Transformation dependence of lead zirconate titanate (PZT) as shown by piezoafm surface mapping of SOL-GEL produced pzt on various substrates.

PZT was grown on STP (Si/SiO2/Ti/Pt (Ti 5nm, Pt 100nm)), SAP (Si/Si3N4/AI/Ti/Pt (Al 100nm, Ti 10nm, Pt 15nm)) and GI (Glass/ITO(Indium Tin Oxide)). In each case the PZT underwent the same heat treatment, 200°C for 2 minutes and then 530°C for 5 minutes. The extent of perovskite formation was evaluated using Piezoresponse force microscopy (PFM). This provided information about the domain orientation and spatial distribution of ferroelectric material in the PZT film. This showed that PZT/STP underwent complete transformation to the perovskite phase. However, for the PZT/SAP and GI incomplete transformation to the perovskite occurred. A system of rosettes surrounded by an amorphous matrix developed. The size and density of the PZT rosettes on the surface was found to be substrate dependent. For Gi/PZT the density of rosettes formation is ca. 1/μm2, compared to 4/μm2 for PZT/SAP. The rosettes for the PZT on GI grow a maximum size of 2μm, which compares to 1μm for PZT on SAP. Differences in the observed growth rate and nucleation density are associated with the back electrode stability and crystal structure, effects that will be discussed in this paper.

Texture of fatty acid Langmuir films studied by means of Brewster angle reflectometry

The compression induced change of the integral reflected intensity of an arachidic acid Langmuir film at the Brewster angle — the so-called reflection isotherm — is analysed to get information about the in-plane anisotropy of the Langmuir film caused by compression and expansion cycles. Based on the matrix method of Berreman a theoretical model, connecting the shape of the reflection isotherms with the domain orientation distribution in the monofilm, is developed. Furthermore, the influence of different counter-ions on the reflection isotherms is studied. The data indicate the formation of ion-specific domain orientation distributions (textures). The reflection isotherms are sensitive to changes in the Langmuir films supramolecular structure which are not reflected by the surface pressure-area isotherms.