Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session Y04: Dielectric & Ferroic Oxides -- Understanding Vacancies and DopantsFocus
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Sponsoring Units: DMP DCOMP Chair: Donald Evans Room: BCEC 107C |
Friday, March 8, 2019 11:15AM - 11:27AM |
Y04.00001: WITHDRAWN ABSTRACT
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Friday, March 8, 2019 11:27AM - 11:39AM |
Y04.00002: Ferromagnetic Resonance in BTO-BFO Films Grown on LSMO Giti Khodaparast, Han-Byul Kang, Benjamin Madon, Min Gyu Kang, Brenden A Magill, Deepam Maurya, Shashank Priya, Henri-Jean M DROUHIN, Jean-Eric Wegrowe, Marcos Alves We synthesized epitaxial BTO-BFO films grown on LSMO with decreased leakage and improved multiferroic properties. This work provides new direction for ferromagnetic resonance studies in high quality BTO-BFO films. We observed small Gilbert damping ( α=0.004) and the absence of large inhomogeneous broadening, in a film with 80 nm thickness of BTO-BFO on LSMO (110). Magnetic insulators, such as BTO-BFO are potentially excellent candidates for pure spin current without the existence of charge current.This new materials system can provid opportunities for spin transfer in multifunctional materials where controlling magnetization or spin current, is crucial toward for developing nanoscale spin-based memory and devices. |
Friday, March 8, 2019 11:39AM - 12:15PM |
Y04.00003: Oxygen exchange kinetics in perovskite oxides: Effects of elastic strain, dislocations, and surfaces Invited Speaker: Bilge Yildiz Interfaces between dissimilar oxides are attracting significant interest for their potential role in accelerating charge transport and surface reaction kinetics. If well understood and controlled, they can provide a new way to enable high-performance solid-oxide fuel cells, separation membranes as well as fast switching memristive devices. For example, recent studies have demonstrated that cobaltite hetero-interfaces exhibit orders of magnitude faster oxygen reduction kinetics compared with either single phase. The interfacial strain fields and electronic interactions between the two phases as well as the effect of these interactions on the surface chemistry are the likely mediators behind such an unprecedented enhancement. The underlying mechanisms must be understood quantitatively, so that we can go beyond isolated and empirically found interface or surface structures to rationally designing dissimilar oxide interfaces with superior properties. In this talk, I will present our findings on how elastic strains, dislocations, and surface chemistry affect the defect chemistry and the charge transport/transfer kinetics, by using atomistic computations and model experiments using thin films. These recent results are encouraging for an improved understanding of oxide hetero-interfaces and surfaces at elevated temperatures, and could enable the discovery of new interfaces with fast oxygen transport and oxygen reduction kinetics. |
Friday, March 8, 2019 12:15PM - 12:27PM |
Y04.00004: Optical spectroscopic study on the oxygen vacancy formation in SrTiO3 single crystals Yunsang Lee, Junhwi Lim, Sang Don Bu We investigated the changes in the emission characteristics of SrTiO3 (STO) single crystals under control of oxygen vacancies by using gamma-ray irradiation. The photoluminescence spectroscopy is useful in probing oxygen vacancies, since the intensity of the visible emission is nearly proportional to the amount of oxygen vacancies. The STO samples were prepared in the directions of (100), (110) and (111). The unirradiated samples were found to show visible emissions near 500 nm, indicating they should have initially had some oxygen vacancies. With the gamma-ray irradiation increasing up to 100 kGy, the visible emission was found to increase for all three directions of STO samples. Interestingly, the variation in emission was dependent on the surface orientation of the STO: the intensity variation was greatest in the (111) sample. We discussed our results in relation to the surface energy of the STO. |
Friday, March 8, 2019 12:27PM - 12:39PM |
Y04.00005: Prediction and Direct Observation of Apical Oxygen Vacancies in YBCO Steven Hartman, Bernat Mundet Bolos, Jaume Gazquez, Rohan Mishra Prior study of the high-temperature superconductor YBa2Cu3O7-x (YBCO) has revealed the fundamental role of oxygen vacancies in controlling the material’s superconductivity. At low oxygenation (x > 0.5), the vacancies are ordered in the CuO chains, and nearly all studies of the vacancies in YBCO, even for high oxygenation (x » 0) have focused on the chain vacancy for this reason. However, optimally doped YBCO (x = 0.06) has relatively few vacancies, and these do not form ordered patterns, which are easy to detect using diffraction techniques. In this work, we use first-principles calculations and scanning transmission electron microscopy (STEM) to investigate vacancy formation in optimally doped YBCO. Our calculations show that at optimal doping, vacancy formation at the apical site is equally favorable to chain vacancy formation. To confirm this prediction, we use the atomic resolution of STEM to provide direct observation of these apical vacancies under certain experimental conditions. We also characterize the effects of apical vacancies on YBCO’s electronic properties, using the calculated density of electronic states and experimental electron energy loss spectroscopy. |
Friday, March 8, 2019 12:39PM - 12:51PM |
Y04.00006: Coexistence of polar displacements and conduction in doped ferroelectrics: an ab initio comparative study Chengliang Xia, Yue Chen, Hanghui Chen Degenerately doped ferroelectrics may create an approximate polar metallic phase. We use first-principle calculations to investigate n-doped LiNbO3-type oxides (LiNbO3 as the prototype) and compare to perovskite oxides (BaTiO3 as the prototype). In rigid-band approximation, substantial polar displacements in n-doped LiNbO3 persist even at 0.3e/f.u., while that in n-doped BaTiO3 quickly get suppressed and completely vanish at 0.1e/f.u. Supercell calculations which use oxygen vacancies as electron donors support results from rigid-band approximation and provide more detailed charge distribution. We find that in n-doped LiNbO3, conduction electrons are not as uniformly distributed as in n-doped BaTiO3. Insulating and conducting Nb sites coexist but substantial cation displacements are observed throughout n-doped LiNbO3. Our work shows that polar distortions and conduction can coexist in a wide range of electron concentration in n-doped LiNbO3, which is a practical approach to create an approximate polar metallic phase. Our results also show that Li displacements are not solely induced by Nb-O displacements, which may shed light on the origin of ferroelectricity in LiNbO3. |
(Author Not Attending)
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Y04.00007: Proton-transfer Ferroelectricity of Trans-Unitcell Ion-Displacement and Multiferroic Soliton in Sodium and Potassium Hydroxides Menghao Wu We show first-principles evidence of robust proton-transfer ferroelectricity with considerable polarization in sodium and potassium hydroxides, which are ready for commercial scale production. Moreover, even a small amount of proton vacancies can completely change the mode of proton-transfer from intra-unitcell to trans-unitcell, giving rise to a hitherto unreported type of multiferroic soliton with “mobile” magnetism and a tremendous polarization that can be two orders of magnitude higher compared with most perovskite ferroelectrics. Their vertical polarizations of thin-film are robust against depolarizing field, rendering various designs of 2D ferroelectric field-transistors with non-destructive readout and ultra-high on/off ratio via sensing the switchable metallic/insulating state. |
Friday, March 8, 2019 1:03PM - 1:15PM |
Y04.00008: Imaging current filaments created by the metal-insulator transition in vanadium dioxide Mark Field, Christopher Hillman, Philip Stupar, Euan Ramsay, James Vickers Vanadium dioxide (VO2) undergoes a reversible metal-insulator transition at 67 °C, changing from a semiconductor at low temperatures to a metal at high temperatures. The crystal structure changes from monoclinic to rutile and this structural change is sufficient to modify the bandstructure. Current biasing a thin film of VO2 shows high resistivity Ohmic behavior at low currents, and at higher currents the resistance suddenly drops as the Joule heating is sufficient to trigger the metal - insulator transition. At this point the heating decreases allowing sections of the material to revert to a semiconductor, concentrating the current within a metallic filament. At intermediate currents the metallic filament forms but the low resistance path does not dissipate enough heat to maintain it, and thermal oscillations are observed where the filament repeatedly forms and collapses. In this work we image a metallic filament within a current biased thin film VO2 sample using a laser scanning microscope. We observe the evolution of the filament in time when the device is oscillating, following the formation and collapse of the filament, and measure the time scales for each process. |
Friday, March 8, 2019 1:15PM - 1:27PM |
Y04.00009: Magnetism of BiFeO3 Nanoparticles across its ferroelectric phase transition Alexander Cardona, Edwin RAMOS, Alex Hojem, Andreas Reiber, Ivan Schuller, Juan Ramirez Multiferroics exhibit simultaneous magnetic and ferroelectric ordering. The archetypical multiferroic material, BiFeO3(BFO), has attracted much attention since it has both, high ferroelectric Curie temperature (1103 K) and, high antiferromagnetic Néel temperature (643 K) in bulk. Here we explore a new route of magnetic control via nano-structuration in the form of nanoparticles (NPs). We fabricated BFO NPs by the sol-gel method with different particle sizes. We have found that their magnetic properties at room temperature and down to 2K change drastically by varying the NP size. Here we present magnetometry studies at high temperature up to the ferroelectric phase transition crossing the antiferromagnetic ordering temperature. These measurements were contrasted with XRD at high temperature to map the structural phase transition associate to the ferroelectric distortion. Our results suggest that NP size also modifies the ferroelectric and antiferromagnetic transition, allowing for a full control of the multiferroic ordering. |
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