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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Heteroanionic Ruddlesden-Popper ferroelectrics from anion order and octahedral tilts

We describe a strategy to design ferroelectric heteroanionic materials based on the coupling of anion order and octahedral tilts in n = 1 Ruddlesden-Popper structures, which allows noncentrosymmetric and polar compounds to arise from centrosymmetric anion-ordered structures. Here we investigate the relative phase stabilities of the polymorphs of Sr 2 ScO 3 F and Ca 2 ScO 3 F derived from this coupling using electronic structure calculations. We find that large degrees of octahedral tilting can stabilize different anion orders derived from assembly of [ScO 5 F] 8– octahedra. To further understand the link between octahedral tilting and anion order, we quantitatively separate the contributions of electrostatics and covalent interactions to the stability of tilts. We find that the tilts are driven primarily by covalent interactions and that local out-of-plane polar displacements, induced from the anion order, further stabilize the octahedral tilts through the pseudo-Jahn-Teller effect.

36 MATERIALS SCIENCE↗
DOE OSTI2022

On the Feasibility of 1T Ferroelectric FET Memory Array

To fully exploit the ferroelectric field effect transistor (FeFET) as compact embedded nonvolatile memory for various computing and storage applications, it is desirable to use a single FeFET (1T) as a unit cell and arrange the cells into an array. However, many write mechanisms for an 1T FeFET array reported in the literature are yet to be validated experimentally. In this work, we performed a comprehensive experimental characterization on the write operations in an 1T- NOR and 1T- AND array using n-channel bulk FeFETs. We discovered that: 1) the source/drain contact can only supply minority carriers (i.e., electrons) to the channel for polarization screening during the low- V TH state programming; 2) the body contact can not only supply majority carriers (i.e., holes) for efficient high- V TH state write, but also depletion charge for low- V TH state programming, though with lower efficiency; and 3) during the low/high- V TH programming, only the path that can supply negative/positive screening charges, respectively, need to respond, which necessitates the application of proper write biases on the corresponding terminal. Based on the understanding of these write mechanisms, we show the importance of localized body contact or column-wise body contact for the successful high- V TH state programming. We also show that the previously proposed C- AND write scheme fails to program the FeFET to the low- V TH state for our devices. Finally, we propose several write schemes for both 1T- AND and 1T- NOR arrays for various scenarios providing insights for choosing the appropriate write scheme, which will facilitate the adoption of 1T FeFET memory arrays for emerging applications.

FeFET↗
DOE OSTI2016

Integrating Nano-patterned Ferromagnetic and Ferroelectric Thin Films for Electrically Tunable RF Applications

Tunable radio frequency (RF) components are pivotal elements in frequency-agile and multifunctional systems. However, there is a technical barrier to achieve miniaturized fully electrically tunable RF components. This paper provides and demonstrates the efficacy of a first unique design methodology in developing fully electrically tunable RF components by integrating ferromagnetic (e.g., Permalloy) and ferroelectric (e.g., Lead Zirconate Titanate: PZT) thin films patterns. Permalloy thin film has been patterned in nanometer scale to improve its ferromagnetic resonance frequency (FMR) for RF applications. Tunable inductors are developed with the utilization of different thickness of Permalloy thin film, which show over 50% increment in inductance and over 4% in tunability with DC current. More tunability can be achieved with multiple layers of Permalloy thin film and optimized thickness. A fully electrically tunable slow wave RF transmission line with simultaneously variable inductance and capacitance density has been implemented and thoroughly investigated for the first time. Measured results show that a fixed phase shift of 90° can be achieved from 1.5 GHz to 1.85 GHz continuously by applying external DC current from 0 to 200 mA and external DC voltage from 0 to 15 Volts, respectively.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Single-Event Effects in the Peripheral Circuitry of a Commercial Ferroelectric Random Access Memory

This paper identifies the failure modes of a commercial 130-nm ferroelectric random access memory. The devices were irradiated with heavy-ion and pulsed focused X-ray beams. Various failure modes are observed, which generate characteristic error patterns, affecting isolated bits, words, groups of pages, and sometimes entire regions of the memory array. Furthermore, the underlying mechanisms are discussed.

42 ENGINEERING↗
DOE OSTI2023

Polarity effects on wake–up behavior of Al 0.94 B 0.06 N ferroelectrics

Wurtzite ferroelectric materials are promising candidates for energy-efficient memory technologies, particularly for applications requiring high operating temperatures. Asymmetric wake-up behaviors, in which the polarization reversal depends both on polarity and cycle number for the first few dozen cycles, must be better understood for reliable device operation. Here, the detailed analysis of the asymmetric wake-up behavior of thin film Al 0.94 B 0.06 N was performed combining time-resolved switching measurements with Rayleigh analysis, piezoelectric measurements, and etching experiments of progressively switched samples. Furthermore, the analysis shows that the gradual opening of the polarization hysteresis loops associated with wake-up is driven by a gradual increase in the domain-wall density and/or domain-wall mobility with electric field cycle to the polarity opposite to the growth polarity. The insights of this discovery will help to guide interface and polarity design in the eventual deployment of reliable devices based on these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

On the polarization dynamics in the presence of flexoelectricity and morphotropic phase boundary in ferroelectrics

It is shown that anomalous piezoelectric properties of epitaxial nanostructures arise on the morphotropic phase boundary (MPB) due to the strong flexoelectric effect on dislocation walls. The MPB (typical of many materials) exhibits a coexistence of various phases and partition of these phases to minimum sizes. This minimum size l{sub c} (nanoscale) is found using the dislocation theory; it coincides with the distance between individual dislocations in dislocation walls, which is much larger than the Burgers vector b, regardless of the type of crystalline material. The flexoelectric coefficients f are estimated taking into account dimensional relations and experimental data on the rotations of ferroelectric nanodomains in multiferroics. These estimates coincide with classical values. The critical value l{sub c} ~ 10b specifies the measured dependence on the dielectric susceptibility χ{sub e}, f ~ χ{sub e}{sup 1/2}. The quantity χ{sub e} depends on the frequency of the ac electric field applied to a sample and on the dislocation density. The Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}/Ni{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramic composite shows typical frequency dispersion of χ{sub e} in a wide frequency range. The frequency dependence of flexoelecric coefficients is shown to reproduce the frequency dependence of permittivity at high frequencies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structure of Relaxor Ferroelectric (1 – 2х)BiScO{sub 3} · хPbTiO{sub 3} · хPbMg{sub 0.33}Nb{sub 0.67}O{sub 3} with х = 0.42 in the Polarized and Depolarized States

An X-ray diffraction study of ceramic samples of relaxor ferroelectric (1 – 2х)BiScO{sub 3} · хPbTiO{sub 3} · хPbMg{sub 0.33}Nb{sub 0.67}O{sub 3} with х = 0.42 in the polarized and depolarized states has been performed. It is established by Rietveld method that in both cases samples contain two perovskite-like phases, which are solid solutions. One of them has cubic symmetry. The second phase is characterized by the polar tetragonal sp. gr. P4mm in the polarized state and the monoclinic noncentrosymmetric sp. gr. Cm in the depolarized state.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Theory of multinonlinear media and its application to the soliton processes in ferrite–ferroelectric structures

A theory is developed to describe the wave processes that occur in waveguide media having several types of nonlinearity, specifically, multinonlinear media. It is shown that the nonlinear Schrödinger equation can be used to describe the general wave process that occurs in such media. The competition between the electric wave nonlinearity and the magnetic wave nonlinearity in a layered multinonlinear ferrite–ferroelectric structure is found to change a total repulsive nonlinearity into a total attractive nonlinearity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Electrooptical effect in the plasmon structure glass–In{sub 2}O{sub 3}: Sn–ferroelectric–Al with a subwavelength grating

The spectral features of the electrooptical effect, in which an applied voltage changes the refractive index of a ferroelectric copolymer, are studied. Three nanostructures are investigated: two nanostructures play an auxiliary role, and the basic structure consists of a glass substrate, a transparent ITO (In{sub 2}O{sub 3}: Sn) layer, active copolymer layer, and an Al layer with a nanograting. This grating with a period of 400 nm meets the conditions of excitation of plasmon resonances. The light transmission coefficients of all structures are analyzed in the spectral range 400–900 nm. The transmission spectra have two characteristic plasmon dips, one of which is related to the copolymer–ITO interface and the other, to the copolymer–Al interface. The aluminum and ITO layers play the role of electrodes, which supply voltage pulses (from 0 to 15 V) to the copolymer layer. When studying the electrooptical effect, we detected spectral shifts in plasmon resonance bands when the amplitudes of both positive and negative voltage pulses (quadratic effect) increase. These shifts change the effective refractive indices (n{sub eff}) of the structural elements, reaching the minimum negative increment Δ{sub eff} =–0.06.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Short-Range Order in Amorphous and Crystalline Ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2}

The microstructures of amorphous and polycrystalline ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO{sub 2} and ZrO{sub 2}. After rapid thermal annealing, the mixed Hf{sub 0.5}Zr{sub 0.5}O{sub 2} oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands are formed in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO{sub 2} and ZrO{sub 2}. The presence of the HfO{sub 2} and ZrO{sub 2} phases in the Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films is also detected by ellipsometry.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the Electret Effect in Polymer–Ferroelectric Piezoceramic Composites with Various Values of the Electronegativity of the Polymer Matrix and Piezophase Cations

The influence of the electronegativity of phases, which is controlled by composite crystallization under the conditions of the effect of the electric discharge and covalence of piezophase cations, on the formation mechanism of the stable electret effect is determined. The specific features of the formation of the electret effect in composites based on polyolefins (HDPE, PP), fluorine-containing polymers (F42), and ferroelectric piezoelectric ceramics of the family of lead zirconate–titanate (Pb(Zr,Ti)O{sub 3}) crystallized under conditions of the effect of electric discharge plasma, are revealed. A physical model of electret composites taking into account the role of homocharges and heterocharges formed in a composite by its dispersion with piezoceramic particles of various structures—rhombohedral, tetragonal, and heterogeneous—is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optical second harmonic generation and its photoinduced dynamics in ferroelectric semiconductor Sn{sub 2}P{sub 2}S{sub 6}

By means of optical pump–probe technique, the ultrafast dynamics of nonlinear optical response of the ferroelectric semiconductor Sn{sub 2}P{sub 2}S{sub 6} crystal excited with a femtosecond laser pulse has been investigated. It has been shown that, under the action of femtosecond pulses, change in optical second harmonic generation occurs in the sample, which can be due to screening of existing electric polarization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Specific features of the ferroelectric state in two-layer barium strontium titanate-based heterostructures

The structural properties of one- and two-layer heterostructures based on the barium–strontium titanate of various compositions deposited by the Frank–Van der Merve on a magnesium oxide substrate have been studied. The heterostructures have been prepared by the rf sputtering of the stoichiometric ceramic targets in a Plazma 50 SE deposition system. The principal difference of this method of deposition from known analogs is that the growth of single-crystal films occurs from a disperse oxide phase formed in the plasma of a high-current rf discharge during the ceramic target sputtering at the cluster level. The peculiarities of the manifestation of the ferroelectric state in the two-layer heterostructures when changing the sequence order of the films with various compositions of barium–strontium titanate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Phase Transitions of KIO{sub 3} Ferroelectrics in Al{sub 2}O{sub 3}-Based Nanoporous Matrices

Temperature dependences of the linear permittivity ε' and the third harmonic amplitude γ{sub 3ω} of composites prepared by introducing ferroelectrics KIO{sub 3} into matrices of porous aluminum oxide Al{sub 2}O{sub 3} with pore sizes of 240 nm were studied. It is found that the IV → III and III → II structural transition temperatures of potassium iodide in Al{sub 2}O{sub 3} pores decrease by 5 K and 24 K, respectively, with respect to bulk KIO{sub 3}. The measurements of the dielectric properties do not reveal V → IV and II → I phase transitions in the composite samples.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Phase Diagrams of Solid Solutions of Relaxor Ferroelectrics from the Dielectric Spectroscopy Data

The dielectric spectra of Pb({sub 1–z})Ba{sub z}(Mg{sub 1/3}Nb{sub 2/3}){sub m}(Zn{sub 1/3}Nb{sub 2/3}){sub y}(Ni{sub 1/3}Nb{sub 2/3}){sub n}Ti{sub x}O{sub 3} (x = 0.25–0.4, y = 0.1130–0.0842, m = 0.4844–0.1298, n = 0.1266–0.4726, z = 0–0.15) ceramics with substitution in both A and B crystallographic positions of the perovskite structure are studied. The system demonstrates a transition from the relaxor state to the normal ferroelectric state in both cases: when the concentration of lead titanate grows and the concentration of barium is reduced. On the basis of experimental results, the x–T and z–T phase diagrams are plotted. Despite different crystal chemical reasons of the relaxor state emergence in the investigated solid solutions, their diagrams demonstrate an evident similarity. We have revealed the disappearance of the temperature hysteresis at the transition to the relaxor state in both cases, which has allowed us to make an assumption of the existence of tricritical points on the corresponding diagrams.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Potential Images of Ferroelectric Domain Structures Formed by Electron Beam in Lithium Niobate Crystals

Ferroelectric domain structures formed by an electron beam in lithium niobate crystals are studied using low-voltage SEM microscopy. The structures are formed in crystals with different conductivity, including samples with high-resistance congruent composition (CLN) and samples with conductivity increased by reductive annealing (RLN). The potential nature of the contrast of the domain structures observed in the secondary electron mode depending on the conductivity of the samples and the direction of spontaneous polarization of the domains is analyzed. It is assumed that the domain contrast in CLN crystals is associated with long-lived charges localized near domain walls and in the irradiated areas. The recorded domain structures in the CLN crystals are visualized on polar and nonpolar cuts. In the RLN crystals with improved conductivity compared to CLN, the potential contrast of the periodic domain structures is found only on the polar cuts, where vector P{sub s} of the domains is perpendicular to the irradiated surface. This contrast is likely because the field of the spontaneous electric polarization charges influences the secondary electrons.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Photoinduced modification of optical properties of ferroelectric PZT thin films

This study investigates ultrafast photoinduced changes in optical properties of ferroelectrics (PZT) on femtosecond to nanosecond timescales, using broadband transient reflectivity studies. Surprisingly, spectral features were observed below the bandgap, which could not be attributed to ground state bleaching, excited state absorption, and/or stimulated emission. A model based on probe energy independent changes in refractive index and extinction coefficient showed good agreement with experimental results. Three relaxation processes were phenomenologically considered for the temporal evolution. Laser-induced heating was ruled out as the cause of short timescale behavior and photorefractive effect was suggested as a potential mechanism for changes in the optical properties.

36 MATERIALS SCIENCE↗