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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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DOE OSTI2015

Raman Vibrations, Domain Structures, and Photovoltaic Effects in A‐Site La‐Modified BiFeO 3 Multiferroic Ceramics

Micro‐Raman spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy ( TEM ), oxygen vacancies, synchrotron X‐ray absorption spectroscopy, magnetizations, optical band gaps, and photovoltaic ( PV ) effects have been studied in (Bi 1− x La x )FeO 3 ( BFO 100 x L) ceramics for x = 0.0, 0.05, 0.10, and 0.15. XRD , Raman spectra, and TEM confirm a rhombohedral R 3 c symmetry with the tilted FeO 6 oxygen octahedra in all compounds. The low‐frequency Raman vibrations become broader and shift toward higher frequency as La 3+ increases. Fe K‐edge synchrotron X‐ray absorptions reveal that Fe 3+ valence and Fe–O–Fe bond angle are not modified by the La 3+ substitution. All compounds exhibit a linear antiferromagnetic feature. Optical transmission reveals band gaps in the range of 2.22–2.24 eV. The heterostructures of indium tin oxide ( ITO ) film/(Bi 1− x La x )FeO 3 ceramics/Au film show a p – n junction‐like I – V characteristic behavior. The maximal PV power conversion efficiency can reach 0.19% in ITO / BFO 15L/Au under illumination of λ = 405 nm. A junction‐like theoretical model can reasonably describe open‐circuit voltage and short‐circuit current as a function of illumination intensity.

Tu, Chi‐Shun↗
DOE OSTI2020

Structure and Dynamics of Domains in Ferroelectric Nanostructures – Phase-Field Modeling (Final Technical Report)

Domain pattern formation is one of the most common phenomena in nature and is a topic of immense interest in many fields ranging from materials science and physics to chemistry and biology. This DOE sponsored research project explored the basic science concerning the thermodynamic stability of mesoscale polarization domain patterns and their temporal evolution mechanisms during formation and subsequent switching in ferroelectric nanostructures and heterostructures. The project employed the computational phase-field method in combination of microelasticity and electrostatic theories. The research was carried out in close collaboration with a number of experimental groups who used High Resolution Transmission Electron Microscopy (HRTEM), in situ TEM with Scanning Probe Microscopy (SPM), or Piezoresponse Force Microscopy (PFM) to characterize the domain structures and dynamics of ferroelectric thin films and heterostructures and who grow high-quality ferroelectric and multiferroic thin films using advanced growth techniques such as Molecular Beam Epitaxy (MBE), Pulsed Laser Deposition (PLLD), and sputtering. The research efforts of the project help establish the phase-field method as the most powerful method for understanding and predicting domain structures in ferroelectric thin films and nanostructures. The findings of the project led to the basic understanding of stability and switching mechanisms of ferroelectric domains under different mechanical boundary conditions and under either homogeneous capacitor configurations or local fields using metallic probes as electrodes and the emergence of charged domain walls during domain switching. The project predicted the spatial length scales, temperature ranges, and electromechanical conditions for different polar states in heterostructures and guided the discovery of both transient and stable novel polarization states containing vortex lattices in oxide superlattices. The project resulted in 134 journal publications and 6 PhD theses with all the PhD graduates currently working in either academia or industry within the United States. The basic understanding on the stability of mesoscale polar states and pattern evolution achieved by the project improved our ability to control and engineer properties of ferroelectric thin films and heterostructures for potential applications in nanoscale electronic devices.

36 MATERIALS SCIENCE↗