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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Direct observation of polarization-induced two-dimensional electron/hole gases at ferroelectric-insulator interface

Abstract Two-dimensional electron gas or hole gas (2DEG or 2DHG) and their functionalities at artificial heterostructure interfaces have attracted extensive attention in recent years. Many theoretical calculations and recent experimental studies have shown the formation of alternating 2DEG and 2DHG at ferroelectric/insulator interfaces, such as BiFeO 3 /TbScO 3 , depending on the different polarization states. However, a direct observation based on the local charge distribution at the BiFeO 3 /TbScO 3 interface has yet to be explored. Herein we demonstrate the direct observation of 2DHG and 2DEG at BiFeO 3 /TbScO 3 interface using four-dimensional scanning transmission electron microscopy and Bader charge analysis. The results show that the measured charge state of each Fe/O columns at the interface undergoes a significant increase/reduction for the polarization state pointing away/toward the interface, indicating the existence of 2DHG/2DEG. This method opens up a path of directly observing charge at atomic scale and provides new insights into the design of future electronic nanodevices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Super-resolution and signal separation in contact Kelvin probe force microscopy of electrochemically active ferroelectric materials

In this work, imaging mechanisms in contact Kelvin probe force microscopy (cKPFM) are explored via information theory-based methods. Gaussian processes are used to achieve super-resolution in the cKPFM signal, effectively extrapolating across the spatial and parameter space. Tensor factorization is applied to reduce the multidimensional signal to the tensor convolution of the scalar functions that show a clear trending behavior with the imaging parameters. These methods establish a workflow for the analysis of the multidimensional datasets that can then be related to the relevant physical mechanisms. We also provide an interactive Google Colab notebook that goes through all the analyses discussed in the paper.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Operando single crystal neutron diffraction reveals insight into the field response mechanisms in the hydrogen-bonded KH 2 PO 4 ferroelectric

The mechanism that facilitates polarization reorientation in KH 2 PO 4 (KDP) was investigated using operando single-crystal neutron diffraction. Diffraction data were measured from a KDP single crystal during the application of alternating electric fields and were then binned into 40 increments to enable field-dependent single-crystal structure refinements. The field-dependent structures are compared with an as-grown crystal to determine how the lattice and atomic sites evolve in response to the applied electric fields. These analyses provide evidence that the reorientation of the macroscopic polarization is facilitated through a cooperative change in hydrogen bonding, which results in the reversal of the spontaneous dipole. In addition, a decrease in secondary extinction near the coercive field indicates that the inversion of the macroscopic polarization is achieved through the nucleation and subsequent growth of new domains.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multi-objective Bayesian optimization of ferroelectric materials with interfacial control for memory and energy storage applications

Optimization of materials’ performance for specific applications often requires balancing multiple aspects of materials’ functionality. Even for the cases where a generative physical model of material behavior is known and reliable, this often requires search over multidimensional function space to identify low-dimensional manifold corresponding to the required Pareto front. In this work, we introduce the multi-objective Bayesian optimization (MOBO) workflow for the ferroelectric/antiferroelectric performance optimization for memory and energy storage applications based on the numerical solution of the Ginzburg–Landau equation with electrochemical or semiconducting boundary conditions. MOBO is a low computational cost optimization tool for expensive multi-objective functions, where we update posterior surrogate Gaussian process models from prior evaluations and then select future evaluations from maximizing an acquisition function. Using the parameters for a prototype bulk antiferroelectric (PbZrO 3 ), we first develop a physics-driven decision tree of target functions from the loop structures. We further develop a physics-driven MOBO architecture to explore multidimensional parameter space and build Pareto-frontiers by maximizing two target functions jointly—energy storage and loss. This approach allows for rapid initial materials and device parameter selection for a given application and can be further expanded toward the active experiment setting. The associated notebooks provide both the tutorial on MOBO and allow us to reproduce the reported analyses and apply them to other systems (https://github.com/arpanbiswas52/MOBO_AFI_Supplements).

36 MATERIALS SCIENCE↗
DOE OSTI2024

In situ temperature synthesis and characterization of ferroelectric PZN-4.5PT nanoparticles’ thin films using synchrotron light source

Despite the excellent properties of Pb(Zn 1/3 Nb 2/3 )O 3 -4.5PbTiO 3 (PZN-4.5PT) single crystals, the greatest difficulty for their application on electronic devices is to make them to thin layers related to the difficulty to make them as ceramic materials. In this paper, we use the combined USAXS/SAXS/WAXS instrument at 9ID beamline at APS-ANL for in situ characterization of PZN-4.5PT inorganic perovskite nanoparticles thin films deposited on nanotextured silicon to understand the phase transitions and determine the observed microcrystals' structure. Here, the sample was annealed from ambient to 1000°C. The results revealed structure changes in the nanoparticles' thin films which could be explained by the new phase that can be assigned to the Pb 3 (PO 4 )2-based component. The peak at 31° indicates the presence of the rhombohedral phase perovskites assigned to the nanoparticles. WAXS characterization permitted to identification of many transitions during thermal annealing like dehydration or dihydroxylation of phosphorus gel -OH bonds and internal water.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Flexoinduced ferroelectricity in low-dimensional transition metal dichalcogenides

We developed a Landau-type theory for the description of polar phenomena in low-dimensional transition metal dichalcogenides (TMDs), specifically exploring the flexoelectric origin of the polarization induced by a spontaneous bending and by inversion symmetry breaking due to the interactions with substrate. We consider the appearance of the spontaneous out-of-plane polarization due to the flexoelectric coupling with the strain gradient of the spontaneous surface rippling and surface-induced piezoelectricity. Additionally, performed calculations proved that the out-of-plane spontaneous polarization, originating from the flexoelectric effect in a rippled TMD, is bistable and reversible by a nonuniform electric field. In contrast, the spontaneous polarization induced by a misfit strain and symmetry-sensitive surface-induced piezoelectric coupling, cannot be reversed by an external electric field. Special attention is paid to the spectral analysis of the linear dielectric susceptibility and gain factor, which enhancement is critically important for the observation of the polar phenomena in low-dimensional TMDs by the surface-enhanced vibrational spectroscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Unraveling Hidden Order and Dynamics in a Heterogeneous Ferroelectric System Using Machine Learning

We uploaded two batches of datasets: Batch-a) Equilibrium dynamics at a constant temperature at zero electric-field, with one trajectory each for 4-different defect structures (i.e. SETs 1 to 4). Each trajectory has a time-step of 0.25 fs, and is run for 7775000 time-steps, with snapshots written out every 4 time-steps (i.e. every 1fs); and Batch-b) Non-Equilibrium dynamics at a constant temperature with the same 0.25 fs time-step, but data dumped every 500 times-steps (i.e. every 125fs) for each of the SETs. The total trajectory of each defect structure (i.e. each SETs 1 to 4) is 2800000 time-steps (5600 snapshots), with stepping of electric-field by 0.01 V/Ã…, after every 100,000 time-steps (i.e. every 200 snapshots), from E=0 to E=0.05 V/Ã… to E = -0.05 V/Ã… to E=0.05 V/Ã….

36 MATERIALS SCIENCE↗
DOE OSTI2024

Using interfaces to: create strongly-coupled magnetic-ferroelectrics

Starting at the level of electrons and atoms our long-term goal is to rationally design complex oxide heterostructures and interface-materials with targeted emergent behaviors. This is not a matter of simply optimizing material parameters, but rather begins with understanding a mechanism to control the interplay between the diverse microscopic degrees of freedom prevalent in complex oxides in order to create targeted macroscopic phenomena and ends with the design of new material realizations. These realizations are in turn created with atomic-layer precision, structurally assessed to see that they are the intended realization, and finally their relevant properties are measured. During this program we have developed the scientific ideas necessary to apply this materials-by-design paradigm to the creation of materials offering electrical control of magnetism. At the heart of our approach lies a partnership between theory, synthesis, and characterization. These are the areas of expertise of the three co-PIs, who have worked closely together since their arrival at Cornell. During this project bold ideas on where to put the atoms to provide electrical control of magnetism were met with the latest methods of synthesis science and electron microscopy in an attempt create targeted new multiferroics. Our work applying this materials-by-design methodology to multiferroics has enjoyed multiple successes. The Co-PIs have invented new mechanisms for multiferroics, which provide strong coupling between polarization and magnetism, and reduced them to practice. Specifically, we pioneered multiferroics based on spin-phonon coupling, rotation-driven multiferroicity, and novel geometric multiferroics. Importantly, the latter two of these mechanisms enable the deterministic switching of magnetism by an applied electric field, which is key to the application of multiferroics to future device technologies. Most recently, we performed detailed theoretical analysis on a system involving the combination of magnetoelectric and colossal magnetoresistance behaviors and predict that electrical control of a metal-insulator transition is possible in appropriately strained SmBaMn2O6. The research enabled by this grant led to 63 publications in leading refereed journals including Nature, Nature Materials, Physical Review Letters, and Advanced Materials demonstrating a materials-by-design paradigm to the creation of materials offering electrical control of magnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Vertical and Lateral Etch Survey of Ferroelectric AlN/Al 1-x Sc x N in Aqueous KOH Solutions

Due to their favorable electromechanical properties, such as high sound velocity, low dielectric permittivity and high electromechanical coupling, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al 1-x Sc x N) thin films have achieved widespread application in radio frequency (RF) acoustic devices. The resistance to etching at high scandium alloying, however, has inhibited the realization of devices able to exploit the highest electromechanical coupling coefficients. In this work, we investigated the vertical and lateral etch rates of sputtered AlN and Al 1-x Sc x N with Sc concentration x ranging from 0 to 0.42 in aqueous potassium hydroxide (KOH). Etch rates and the sidewall angles were reported at different temperatures and KOH concentrations. We found that the trends of the etch rate were unanimous: while the vertical etch rate decreases with increasing Sc alloying, the lateral etch rate exhibits a V-shaped transition with a minimum etch rate at x = 0.125. By performing an etch on an 800 nm thick Al 0.875 Sc 0.125 N film with 10 wt% KOH at 65 °C for 20 min, a vertical sidewall was formed by exploiting the ratio of the {$10\overline{11}$ planes and {$1\overline{1}00$ planes etch rates. This method does not require preliminary processing and is potentially beneficial for the fabrication of lamb wave resonators (LWRs) or other microelectromechanical systems (MEMS) structures, laser mirrors and Ultraviolet Light-Emitting Diodes (UV-LEDs). It was demonstrated that the sidewall angle tracks the trajectory that follows the {$\overline{1}2\overline{12}$ of the hexagonal crystal structure when different c/a ratios were considered for elevated Sc alloying levels, which may be used as a convenient tool for structure/composition analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗