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Results for “Polarization transformations”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Study of the ferroelastic phase transition in the tetraethylammonium compound [N(C{sub 2}H{sub 5}){sub 4}]{sub 2}ZnBr{sub 4} by magic-angle spinning and static NMR

The ferroelastic phase transition of tetraethylammonium compound [N(C{sub 2}H{sub 5}){sub 4}]{sub 2}ZnBr{sub 4} at the phase transition temperature (T{sub C}) = 283 K was characterized by magic-angle spinning (MAS) and static nuclear magnetic resonance (NMR), and confirmed by optical polarizing spectroscopy. The structural geometry near T{sub C} was studied in terms of the chemical shifts and the spin-lattice relaxation times T{sub 1ρ} in the rotating frame for {sup 1}H MAS NMR and {sup 13}C cross-polarization (CP)/MAS NMR. The two inequivalent ethyl groups were distinguishable in the {sup 13}C NMR spectrum, and the T{sub 1ρ} results indicate that they undergo tumbling motion above T{sub C} in a coupled manner. From the {sup 14}N NMR results, the two nitrogen nuclei in the N(C{sub 2}H{sub 5}){sub 4}{sup +} ions were distinguishable above T{sub C}, and the splitting in the spectra below T{sub C} was related to the ferroelastic domains with different orientations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Room temperature multiferroic properties of Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3}–Co{sub 0.65}Zn{sub 0.35}Fe{sub 2}O{sub 4} composites

We report the crystal structure, magnetic, ferroelectric, dielectric, and magneto-dielectric properties of [Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3}]{sub (1−x)}[Co{sub 0.65}Zn{sub 0.35}Fe{sub 2}O{sub 4}]{sub x}: (x = 0.1, 0.2, 0.3, and 0.4) composites. Rietveld refinement results of X-ray diffraction patterns confirm the formation of these composites for all x values. All the composites show well-saturated ferroelectric and ferromagnetic hysteresis (multiferroic-composite behavior) at room temperature. With increase in Co{sub 0.65}Zn{sub 0.35}Fe{sub 2}O{sub 4} (CZFO) content an increase in saturation magnetization, and decrease in saturation polarization, remanent polarization, and dielectric constant are observed. The ferroelectric phase transition temperature increases with increase in CZFO content. All of the compositions undergo second-order ferroelectric phase transitions, which can be explained by Landau-Devonshire theory. The recoverable energy density (∼0.20 to 0.04 J/cm{sup 3}) and charge-curve energy density (∼0.84 to 0.11 J/cm{sup 3}) decrease with increase in the CZFO content. The room-temperature magneto-dielectric measurements provide direct evidence of magneto-electric coupling via strain at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Carrier transport in layered semiconductor (p-GaSe)-ferroelectric (KNO{sub 3}) composite nanostructures

The current-voltage characteristics and frequency dependences of the impedance of composite nanostructures fabricated on the basis of layered anisotropic semiconductor p-GaSe and ferroelectric KNO{sub 3} are studied. Multilayer nanostructures were obtained by introducing nanoscale pyramidal ferroelectric inclusions into a layered GaSe matrix. Hysteresis phenomena in current-voltage characteristics and abrupt changes in the conductance and capacitance in frequency dependences of the impedance are detected. These phenomena are associated with the collective effect of electric polarization switching in nanoscale 3D ferroelectric inclusions in the layered matrix, features of its local deformation, and polytype phase transitions in this matrix. X-ray, atomic-force microscopy, and impedance studies in a low (B < 400 mT) magnetic field show that the electrical characteristics of nanostructures are associated with the Maxwell-Wagner effect in nanostructures, the formation of quantum wells in GaSe during deformation of crystals in the region of nanoscale inclusion localization, and carrier tunneling in the structures.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Ferroelectric domain morphology and structure in Li-doped (K,Na)NbO{sub 3} ceramics

We prepared Li{sub 0.02}(K{sub 0.45}Na{sub 0.55}){sub 0.98}NbO{sub 3} (KNN) ceramics using a conventional solid-state sintering method and investigated the domain structure and morphology using a piezoresponse force microscope in these material systems. The abnormal grain consisted of nano-sized subgrains, which were an elementary unit of the domain formation, with a size of approximately 100 nm. They were self-assembled and grew along the <001>{sub o} directions. In the orthorhombic KNN ceramics, the 90 Degree-Sign domains were dominantly distributed and all wedges were 60 Degree-Sign wedges. The polarization vectors and geometrical configurations were analyzed and suggested in the banded twins. The observation of angles between (010){sub o} and (011){sub o} showed that the large grains experienced severe stress resulting in the deformation of the unit cell configuration during the phase transition. The S-walls were preferred as 120 Degree-Sign domain walls and were assigned to (1/0.27/1){sub c}.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Thickness dependent functional properties of PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}/La{sub 0.67}Sr{sub 0.33}MnO{sub 3} heterostructures

The ultra thin ferroelectric PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} (PZT) films with various thicknesses ranging from 100 (P100) to 10 (P10) nm were grown on La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/(LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSMO/LSAT) (001) substrates deposited by pulsed laser deposition technique. The x-ray diffraction patterns of the heterostructures show only (00l) (l = 1 and/or 2) reflections corresponding to the LSAT substrate, PZT, and LSMO layers. The atomic force microscopy studies show that the root mean square surface roughnesses of P100 and P10 films are 2.39 and 0.99 nm, respectively. An increase of both real (ε′) and imaginary (ε″) permittivities was observed when thickness of PZT increases from 10 nm to 100 nm. Temperature dependent ε′ presents an anomaly, related to ferromagnetic-metal to paramagnetic-insulator transition of the LSMO, in the range of 350–500 K. The dielectric anomalies and magnetic phase transition temperature shifted to the lower temperature values with decrease in the PZT films thicknesses. The values of the remanent polarization (P{sub r}) and coercive field (E{sub c}) of the heterostructures were in the range of 24–42 μC/cm{sup 2}–170–1300 kV/cm. An appreciable increase of saturated magnetization (M{sub s}) was observed with increase of PZT layer thickness. The average M{sub s} values of PZT/LSMO heterostructure were 170, 150, 100, and 45 emu/cm{sup 3} for 100, 50, 25, and 10 nm at 300 K, respectively. Enhancement in magnetization with increase in PZT thickness may be due to the interface effect between PZT/LSMO layers.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Enhanced magnetism-generated ferroelectricity in highly frustrated Fe-doped Ho{sub 2}Ti{sub 2}O{sub 7}

We present careful experiments on the ferroelectric (FE), dielectric, and magnetic behaviors of Ho{sub 2−x}Fe{sub x}Ti{sub 2}O{sub 7} with Fe{sup 3+} substitution for Ho{sup 3+}. A remarkable enhancement of polarization up to 235 μC/m{sup 2} is obtained at a low level x = 0.08, accompanied with the FE transition up to ∼80 K. The ac susceptibility under magnetic fields shows an expected saturated maximum in the real part χ′, along with an unexpected frequency-dependent peak in the imaginary part χ″, indicating unusual slow spin relaxation. The coupled correlated spin domains through dipolar interaction are argued to give rise to nonzero electric-dipole via Dzyaloshinskii-Moriya interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Multiferroic tunnel junctions and ferroelectric control of magnetic state at interface (invited)

As semiconductor devices reach ever smaller dimensions, the challenge of power dissipation and quantum effect place a serious limit on the future device scaling. Recently, a multiferroic tunnel junction (MFTJ) with a ferroelectric barrier sandwiched between two ferromagnetic electrodes has drawn enormous interest due to its potential applications not only in multi-level data storage but also in electric field controlled spintronics and nanoferronics. Here, we present our investigations on four-level resistance states, giant tunneling electroresistance (TER) due to interfacial magnetoelectric coupling, and ferroelectric control of spin polarized tunneling in MFTJs. Coexistence of large tunneling magnetoresistance and TER has been observed in manganite/(Ba, Sr)TiO{sub 3}/manganite MFTJs at low temperatures and room temperature four-resistance state devices were also obtained. To enhance the TER for potential logic operation with a magnetic memory, La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/BaTiO{sub 3}/La{sub 0.5}Ca{sub 0.5}MnO{sub 3} /La{sub 0.7}Sr{sub 0.3}MnO{sub 3} MFTJs were designed by utilizing a bilayer tunneling barrier in which BaTiO{sub 3} is ferroelectric and La{sub 0.5}Ca{sub 0.5}MnO{sub 3} is close to ferromagnetic metal to antiferromagnetic insulator phase transition. The phase transition occurs when the ferroelectric polarization is reversed, resulting in an increase of TER by two orders of magnitude. Tunneling magnetoresistance can also be controlled by the ferroelectric polarization reversal, indicating strong magnetoelectric coupling at the interface.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Surface and finite size effects impact on the phase diagrams, polar, and dielectric properties of (Sr,Bi)Ta{sub 2}O{sub 9} ferroelectric nanoparticles

In the framework of the thermodynamic approach Landau-Ginzburg-Devonshire (LGD) combined with the equations of electrostatics, we investigated the effect of polarization surface screening on finite size effects of the phase diagrams, polar, and dielectric properties of ferroelectric nanoparticles of different shapes. We obtained and analyzed the analytical results for the dependences of the ferroelectric phase transition temperature, critical size, spontaneous polarization, and thermodynamic coercive field on the shape and size of the nanoparticles. The pronounced size effect of these characteristics on the scaling parameter, the ratio of the particle characteristic size to the length of the surface screening, was revealed. Also our modeling predicts a significant impact of the flexo-chemical effect (that is a joint action of flexoelectric effect and chemical pressure) on the temperature of phase transition, polar, and dielectric properties of nanoparticles when their chemical composition deviates from the stoichiometric one. We showed on the example of the stoichiometric nanosized SrBi{sub 2}Ta{sub 2}O{sub 9} particles that except the vicinity of the critical size, where the system splitting into domains has an important role, results of analytical calculation of the spontaneous polarization have a little difference from the numerical ones. We revealed a strong impact of the flexo-chemical effect on the phase transition temperature, polar, and dielectric properties of Sr{sub y}Bi{sub 2+x}Ta{sub 2}O{sub 9} nanoparticles when the ratio Sr/Bi deviates from the stoichiometric value of 0.5 within the range from 0.35 to 0.65. From the analysis of experimental data, we derived the parameters of the theory, namely, the coefficients of expansion of the LGD functional, the contribution of flexo-chemical effect, and the length of the surface screening.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Electro-caloric effect in lead-free Sn doped BaTiO{sub 3} ceramics at room temperature and low applied fields

Structural, dielectric, ferroelectric (FE), {sup 119}Sn Mössbauer, and specific heat measurements of polycrystalline BaTi{sub 1–x}Sn{sub x}O{sub 3} (x = 0% to 15%) ceramics are reported. Phase purity and homogeneous phase formation with Sn doping is confirmed from x-ray diffraction and {sup 119}Sn Mössbauer measurements. With Sn doping, the microstructure is found to change significantly. Better ferroelectric properties at room temperature, i.e., increased remnant polarization (38% more) and very low field switchability (225% less) are observed for x = 5% sample as compared to other samples and the results are explained in terms of grain size effects. With Sn doping, merging of all the phase transitions into a single one is observed for x ≥ 10% and for x = 5%, the tetragonal to orthorhombic transition temperature is found close to room temperature. As a consequence better electro-caloric effects are observed for x = 5% sample and therefore is expected to satisfy the requirements for non-toxic, low energy (field) and room temperature based applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A comparative investigation on structure and multiferroic properties of bismuth ferrite thin films by multielement co-doping

Highlights: • Multielement (Tb, Cr and Mn) co-doped BiFeO{sub 3} films were fabricated by CSD method. • Multielement co-doping induces a structural transition. • It is found effective to stabilize the valence of Fe ions at +3 by the strategy. • The co-doping at A/B-sites gives rise to the superior multiferroic properties. - Abstract: (Tb, Cr and Mn) multielement co-doped BiFeO{sub 3} (BTFCMO) thin films were prepared by the chemical solution deposition method on fluorine doped tin oxide (FTO) substrates. X-ray diffraction, Rietveld refinement and Raman analyses revealed that a phase transition from rhombohedral to triclinic structure occurs in the multielement co-doped BiFeO{sub 3} films. It is found that the doping is conducive to stabilizing the valence of Fe ions and reducing leakage current. In addition, the highly enhanced ferroelectric properties with a huge remanent polarization (2P{sub r}) of 239.6 μC/cm{sup 2} and a low coercive field (2E{sub c}) of 615.6 kV/cm are ascribed to the well film texture, the structure transition and the reduced leakage current by the co-doping. Moreover, the structure transition is the dominant factor resulting in the significant enhancement observed in magnetization (M{sub s} ∼ 10.5 emu/cm{sup 3}), owing to the collapse of the space-modulated spin structure. In this contribution, these results demonstrate that the multielement co-doping is in favor of the enhanced multiferroic properties of the BFO films for possible multifunctional applications.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Magnetostructural phase transition in electroless-plated Ni nanoarrays

Ni nanoarrays were synthesized by electroless-plating and shaped by an anodic aluminum oxide template. The as-plated arrays exhibited superparamagnetic (SM) ordering resulting from nanocrystalline microstructure. Ferromagnetic (FM) ordering was found to be restored as the arrays' crystallinity was enhanced upon post-annealing. The microstructure (crystallinity) and the FM ordering are strongly coupled, revealing a magneto-structural correlation for the arrays. The magnetostructural properties of the arrays can be controlled by post-annealing, where the magnetization is proportional to the annealing temperature. The electroless-plated arrays synthesized in this work display magnetic anisotropy not found in electroplated ones. This is likely attributed to the nature of the clusterlike microstructure, whose cluster-boundaries may confine the FM rotation within the cluster. The spin-polarization was probed by x-ray magnetic circular dichroism while the arrays underwent the SM{yields}FM phase transition. The sum-rules results reveal that the total magnetization of the arrays is dominated by spin moment (m{sub spin}). The change in m{sub spin} is responsible for the SM{yields}FM phase transition upon annealing, as well as for the loss of magnetization upon temperature increase that we observed macroscopically.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Investigation of electrical behavior and dielectric properties in polycristalline Pr0.8Sr0.2MnO3 manganite perovskite

Highlights: • Transport properties of Pr{sub 0.8}Sr{sub 0.2}MnO{sub 3} are investigated in a large range of temperature (80–500 K) and frequency (40–10{sup 7} Hz). • DC measurements show two conduction mechanisms at low and high temperature. • The complex impedance shows that our structure obeys at Cole-Cole model. • Dielectric results reveal a dielectric transition which is well fitted by Curie-Weiss law. • AC conductivity is described by Jonscher power law. The NSPT and Drude models are used to describe the conduction mechanism. - Abstract: The electrical and dielectric properties of Pr{sub 0.8}Sr{sub 0.2}MnO{sub 3} perovskite prepared by the solid-state method were investigated. The complex impedance results showed the contribution of grain and grain boundaries in the conduction mechanism. The dielectric data have confirmed the presence of interfacial polarization in the structure. Moreover, a dielectric transition fitted by Curie-Weiss law was observed. Besides, the observed relaxation diffuse phase transition is attributed to a strong heterogeneity introduced by the substitution of Pr by Sr ions. DC electrical measurements indicate that the structure exhibits a semiconductor behavior and the conductivity is governed by hopping process. The AC conductivity measurements show a clear semiconductor-metallic transition at high temperatures. The AC conductivity data can be divided into two parts, the first of which is a semiconductor one, described by the NSPT model, at low temperatures and the second is a metallic regime, fitted by the classical Drude model, at high temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Ferroelectric and dielectric properties of ferrite-ferroelectric ceramic composites

Particulate composites of ferrite and ferroelectric phases with xNiFe{sub 2}O{sub 4} (NF) and (1 - x)Pb{sub 0.988}(Zr{sub 0.52}Ti{sub 0.48}){sub 0.976}Nb{sub 0.024}O{sub 3} (where x = 2, 10, 20, 30, 50, 70, and 100 wt. %) were prepared in situ by sol-gel method. The presence of a diphase composition was confirmed by X-ray diffraction while the microstructure of the composites was studied by scanning electron microscopy revealing a good mixing of the two phases and a good densification of the bulk ceramics. The dielectric permittivity shows usual dielectric dispersion behavior with increasing frequency due to Maxwell-Wagner interfacial polarization. AC conductivity measurements made in frequency range 1 Hz-1 MHz suggest that the conduction process is due to mixed polaron hopping. The effect of NF phase concentration on the P-E and M-H hysteresis behavior and dielectric properties of the composites was investigated. At low NF concentration a sharp ferro-paraelectric transition peak can be observed at around 360 Degree-Sign C while for higher NF concentrations a trend to a diffuse phase transition occurs. All the composite samples exhibit typical ferromagnetic hysteresis loops, indicating the presence of ordered magnetic structure.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Formation of snowflake domains during fast cooling of lithium tantalate crystals

Formation of the original dendrite snowflake-shape domains during fast cooling after heating above phase transition temperature by pulse laser irradiation was revealed in congruent lithium tantalate crystals. The effect was attributed to polarization reversal under the action of spatially nonuniform pyroelectric field. Two stages of the domain shape evolution at the surface were separated: (1) growth of circular domains by sideways motion of the domain walls and (2) backswitching leading to formation of the snowflake domains. The simulated spatial distribution of the pyroelectric field in regular two-dimensional structure was used for an explanation of the obtained results. The backswitching process in the surface layer has been attributed to change of the sign of the pyroelectric field at the domain wall. The snowflake domain shape is caused by the formation of isolated nanodomain fingers and hampering of their merging.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Domain configuration changes under electric field-induced antiferroelectric-ferroelectric phase transitions in NaNbO{sub 3}-based ceramics

We recently developed a feasible crystal chemistry strategy to stabilize the antiferroelectricity in NaNbO{sub 3} through a chemical substitution to decrease the tolerance factor and increase the average electronegativity of the system [Shimizu et al., Dalton Trans. 44, 10763 (2015) and Guo et al., J. Appl. Phys. 117, 214103 (2015)]. Two novel lead-free antiferroelectric (AFE) solid solutions, (1-x)NaNbO{sub 3}-xCaZrO{sub 3} and (1-x)NaNbO{sub 3}-xSrZrO{sub 3}, have been found to exhibit the double polarization hysteresis typical of a reversible AFE ↔ ferroelectric (FE) phase transition. In this study, as demonstrated by (1-x)NaNbO{sub 3}-xCaZrO{sub 3} system, the influence of chemical modification and electrical poling on the AFE/FE phase stability was investigated, primarily focusing on the microstructural and crystallographic evolutions. Together with the macroscopic polarization hysteresis measurements, a well-demonstrated structure-property relationship was presented. It was found that the CaZrO{sub 3} substitution into NaNbO{sub 3} can effectively destabilize the FE Q phase and correspondingly lead to a spontaneous reverting to AFE P phase. In contrast to the reversible AFE ↔ FE phase transition, the domain morphology evolution exhibits irreversible nature with a growing process of the orientational domains after applying electric field. Moreover, a multiple-zone axes electron diffraction map of P and Q phases has been summarized and is believed to be an efficient diagram to determine the AFE/FE nature of the NaNbO{sub 3}-based systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} ceramics

The phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} lead-free ceramics were investigated systematically. The loss tangent of poled sample shows a broad peak when heating to about 80 °C, i.e., depolarization temperature T{sub d}. The polarization-electric field hysteresis loops at different temperature exhibit the feature of ferroelectric (FE)- antiferroelectric (AFE) phase transition and the co-existence of FE and AFE phase. The pyroelectric coefficients curve confirms its diffusion behaviors. The initial hysteresis loop and switching current curves under T{sub d} indicate the co-existence of FE and AFE phase. The domain morphology of transmission electron microscopy supports the co-existence of FE and AFE phase. Our work not only exhibit that the FE and AFE phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} ceramics but also they may be helpful for further investigation on lead-free ceramics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Dynamical mean-field theory and weakly non-linear analysis for the phase separation of active Brownian particles

Recently, we have derived an effective Cahn-Hilliard equation for the phase separation dynamics of active Brownian particles by performing a weakly non-linear analysis of the effective hydrodynamic equations for density and polarization [Speck et al., Phys. Rev. Lett. 112, 218304 (2014)]. Here, we develop and explore this strategy in more detail and show explicitly how to get to such a large-scale, mean-field description starting from the microscopic dynamics. The effective free energy emerging from this approach has the form of a conventional Ginzburg-Landau function. On the coarsest scale, our results thus agree with the mapping of active phase separation onto that of passive fluids with attractive interactions through a global effective free energy (motility-induced phase transition). Particular attention is paid to the square-gradient term necessary for the phase separation kinetics. We finally discuss results from numerical simulations corroborating the analytical results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Strain tunable ferroelectric and dielectric properties of BaZrO{sub 3}

The crucial role of epitaxial (in-plane) strain on the structural, electronic, energetic, ferroelectric, and dielectric properties of BaZrO{sub 3} (BZO) is investigated using density-functional theory calculations. We demonstrate that the BZO crystal subjected to a critical compressive (or tensile) strain exhibits non-trivial spontaneous polarization that is higher than that of well-known ferroelectrics BaTiO{sub 3}, while the BZO crystal is essentially paraelectric in the absence of strain. The electronic structure and Born-effective-charge analyses elucidate that the strain-induced paraelectric-to-ferroelectric transition is driven by the orbital hybridization of d-p electrons between zirconium and oxygen. Through the strain-induced paraelectric-to-ferroelectric phase transition, the dielectric response of BZO is significantly enhanced by the in-plane strain. The tensile strain increases the in-plane dielectric constant by a factor of seven with respect to that without the strain, while the compression tends to enhance the out-of-plane dielectric response. Therefore, strain engineering makes BZO an important electromechanical material due to the diversity in ferroelectric and dielectric properties.

36 MATERIALS SCIENCE↗