Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P26: Insulators: Ferroelectrics and Applications |
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Sponsoring Units: DCMP DMP FIAP Chair: Mina Yoon, Oak Ridge National Laboratory Room: 325 |
Wednesday, March 16, 2016 2:30PM - 2:42PM |
P26.00001: Relative stability of ferroelectric and antiferroelectric states in (Na$_{\mathrm{0,5}}$Bi$_{\mathrm{0,5}})$TiO$_{\mathrm{3}}$-based solid solutions V. Sobolev, V. M. Ishchuk, L. G. Gusakova, N. G. Kisel, D. V. Kuzenko, N. A. Spiridonov Influence of the B-site ion substitutions on the of relative stability of the antiferroelectric and ferroelectric phases in [(Na$_{\mathrm{0.5}}$Bi$_{\mathrm{0.5}})_{\mathrm{0.80}}$Bà$_{\mathrm{0.20}}$](Ti$_{\mathrm{1-x}}$B$_{\mathrm{x}})$O$_{\mathrm{3}}$ (NBT-BT) solid solutions has been investigated. Zirconium and tin ions along with (In$_{\mathrm{0.5}}$Nb$_{\mathrm{0.5}})$, (Fe$_{\mathrm{0.5}}$Nb$_{\mathrm{0.5}})$, and (Al$_{\mathrm{0.5}}$V$_{\mathrm{0.5}})$ ion complexes have been used for substitutions. It is found that an increase of content of the substituting ion results in a near linear variation in the size of the crystal lattice unit cell. The relative stability of the antiferroelectric and ferroelectric phases changes according to the variation of the tolerance factor of solid solution which in turn varies with the change of solid solution composition cause by substitutions. Obtained results demonstrate a predominant influence of the size of substituting ions on the relative stability of the antiferroelectric and ferroelectric states in (Na$_{\mathrm{0.5}}$Bi$_{\mathrm{0.5}})$TiO$_{\mathrm{3}}$-based solid solutions. Our results open a new option for raising the temperature of the ferroelectric to antiferroelectric phase transition NBT-BT compounds. [Preview Abstract] |
Wednesday, March 16, 2016 2:42PM - 2:54PM |
P26.00002: Visible light absorption in La, Cr co-doped SrTiO$_{\mathrm{3}}$ and BaTiO$_{\mathrm{3}}$ for ferroelectric photovoltaics Ryan Comes, Martin McBriarty, Phuong-Vu Ong, Steve Heald, Gerard Carroll, Daniel Gamelin, Keren Freedy, Sergey Smolin, Jason Baxter, Tiffany Kaspar, Mark Bowden, Peter Sushko, Scott Chambers Ferroelectric materials offer intriguing possibilities as photovoltaic materials, as their built-in electric field is ideal for separation of optically-excited electron-hole pairs without the need for a p-n junction. However, the majority of ferroelectrics suffer from a wide optical band gap outside the visible range. By co-doping La and Cr into epitaxial SrTiO$_{\mathrm{3}}$ and BaTiO$_{\mathrm{3}}$ (SLTCO/BLTCO) thin films, we show that absorption in the visible light regime can be achieved with a band gap of \textasciitilde 2.3 eV while preserving ideal stoichiometry. Through x-ray photoelectron spectroscopy, spectroscopic ellipsometry, photoconductivity and ultrafast pump-probe transient reflectance measurements, we show that visible light excitation of Cr 3d valence electrons into the Ti 3d conduction band produces optical carriers. Using piezoresponse force microscopy and polarized x-ray absorption fine structure measurements, we measure the ferroelectric polarization of the doped BLTCO films. These results are compared to density functional theory models to understand the optical and structural properties of the materials. [Preview Abstract] |
Wednesday, March 16, 2016 2:54PM - 3:06PM |
P26.00003: ABSTRACT WITHDRAWN |
Wednesday, March 16, 2016 3:06PM - 3:18PM |
P26.00004: Strain effect on the visible emission in ferroelectric nanotubes: template and wall-thickness effect Yunsang Lee, SangDon Bu, JinKyu Han We investigated the strain effect on temperature-dependent photoluminescence property in the clamped (with template) and free-standing (without template) PbTiO$_{\mathrm{3}}$ (PTO) nanotubes. The wall-thickness of nanotubes was varied from 25 to 80 nm with the outer diameter fixed to 420 nm. While all nanotubes show sizable green/yellow emission, the temperature dependent shift of the emission energy is significantly suppressed in the clamped PTO nanotubes, which is attributed to the lattice strain driven by the template clamping. This clamping effect is more significant for thinner nanotubes. Even in the free-standing PTO nanotubes the temperature-dependence of emission is affected by the wall-thickness. The similar behavior is identified in the Pb(Zr,Ti)O$_{\mathrm{3}}$ nanotubes. Our finding is the clear manifestation of the template and geometrical shape effect on the optical property of the nanotubes. [Preview Abstract] |
Wednesday, March 16, 2016 3:18PM - 3:30PM |
P26.00005: Negative Refractive Index Materials for Optical Range of Spectrum Vladimir Sobolev, Valerii Ishchuk A new method of manufacturing of negative refractive index media is presented. It is demonstrated that one can use of the controlled decomposition of solid solutions of oxides with perovskite crystal\textbf{ }structure in the state of coexisting domains of the antiferroelectric and ferroelectric phases for manufacturing of such materials. The lead zirconate titanate based solid solutions are considered as an example of substances suitable for creation of such materials. Manufactured composites constitute a dielectric antiferroelectric matrix with a structure of conducting interphase boundaries separating domains of the ferroelectric and antiferroelectric phases. The electric conductivity of the interphase boundaries occurs as a result of the local decomposition of the solid solutions in the vicinity of these boundaries. The decomposition process and consequently the conductivity of the interphase boundaries can be controlled by means of external influences. [Preview Abstract] |
Wednesday, March 16, 2016 3:30PM - 3:42PM |
P26.00006: Incommensurate lattice modulations in Potassium Vanadate Bryan Chakoumakos, Arnab Banerjee, Lumsden Mark, Huibo Cao, Jong-Woo Kim, Christina Hoffman, Xiaoping Wang Potassium Vanadate (K$_{\mathrm{2}}$V$_{\mathrm{3}}$O$_{\mathrm{8}})$ is an S $=$ \textonehalf 2D square lattice antiferromagnet that shows spin reorientation indicating a strong coupling between the magnetism and its dielectric properties with a promise of rich physics that promises multiferroicity. These tangible physical properties are strongly tied through a spin-lattice coupling to the underlying lattice and superlattice behavior. It has a superlattice (SL) onsetting below T$_{\mathrm{c}}=$115 K with an approximate [3 x 3 x 2] modulation. Here we present our recent experiments at TOPAZ beamline at SNS which for the first time proves conclusively that the lattice modulations are incommensurate, with an in-plane Q of 0.315. We will also show our attempts to refine the data using JANA which requires a redefinition of the lattice, as well as the temperature and Q dependence of the superlattice modulation measured using neutrons at HFIR and synchrotron x-rays at APS. Our results are not only relevant for the ongoing search of multifunctional behavior in K$_{\mathrm{2}}$V$_{\mathrm{3}}$O$_{\mathrm{8\thinspace }}$but also generally for the superlattice modulations observed in a large family of fresnoites. [Preview Abstract] |
Wednesday, March 16, 2016 3:42PM - 3:54PM |
P26.00007: Properties of Transition Metal Doped Alumina Erik Nykwest, Krista Limmer, Ray Brennan, Victoria Blair, Rampi Ramprasad Crystallographic texture can have profound effects on the properties of a material. One method of texturing is through the application of an external magnetic field during processing. While this method works with highly magnetic systems, doping is required to couple non-magnetic systems with the external field. Experiments have shown that low concentrations of rare earth (RE) dopants in alumina powders have enabled this kind of texturing. The magnetic properties of RE elements are directly related to their f orbital, which can have as many as 7 unpaired electrons. Since d-block elements can have as many as 5 unpaired electrons the effects of substitutional doping of 3d transition metals (TM) for Al in alpha (stable) and theta (metastable) alumina on the local structure and magnetic properties, in addition to the energetic cost, have been calculated by performing first-principles calculations based on density functional theory. This study has led to the development of general guidelines for the magnetic moment distribution at and around the dopant atom, and the dependence of this distribution on the dopant atom type and its coordination environment. It is anticipated that these findings can aid in the selection of suitable dopants help to guide parallel experimental efforts. [Preview Abstract] |
Wednesday, March 16, 2016 3:54PM - 4:06PM |
P26.00008: Incursion of water and Cu ions into porous low dielectric constant (LKD) thin films and interconnects resulting in damage, time dependent dielectric breakdown (TDDB) and decreased lifetime and reliability. Robert Laibowitz, Archana Raja, Thomas Shaw, Eric Liniger, Stephan Cohen Porous dielectrics, their interfaces and related processing details provide many opportunities for water and Cu incursion. The Cu typically starts as part of the electrode and needs a liner to keep it away from the dielectric. As scaling continues thinner liners and imperfections in the in the liner layer can expose the CU to the LKD. This will lead to TDDD with greatly reduced lifetimes. Water exposure can come from processing or through defects in the passivation layer. Most studies of these breakdown effects have been accomplished using accelerated DC measurements in which the sample is destroyed. Dielectric relaxation provides a new set of measurements at low fields, low temperatures and reusable samples. In this way we have observed the presence of both physisorbed and chemisorbed water, determined their activation energy of motion and removal of the water by various annealing protocols. Initial measurements of Cu incursion have also been made. Preliminary measurement of samples containing Cu and water and processing damage show reduced reliability. We also have begun studies to determine the minimum liner thickness. . [Preview Abstract] |
Wednesday, March 16, 2016 4:06PM - 4:18PM |
P26.00009: Strong Red Luminescent Twin ZnO Nanorods for Nano-thermometry and Phonon Tunnel Device Application Avanendra Singh, Kartik Senapati, Karunakar Nanda, Biswarup Satpati, Pratap Sahoo Two segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorphous layer have been successfully synthesized using aqueous growth technique. The amorphous layer between the crystalline ZnO sections is tunable with growth parameters and confirmed by transmission electron microscopy. The confocal photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different temperature shows stable and intense red emission with comparably weak UV emission. Red emission from the twin NRs are the consequence of surface defect and structural imperfections of lattice disorder. The disappearance of asymmetry in UV emission after 293K indicates the weak exciton-phonon coupling at higher temperature while the coupling is stronger at lower temperatures. An indirect analysis from phonon bands of PL shows that the amorphous layer acts as a phonon barrier beyond certain thickness. Such crystalline-amorphous-crystalline architecture may be suitable for fundamental studies of the phonon tunneling in nanostructure. We also show that the individual NRs can be used for sensing and mapping of temperature in a wide range of 80-373 K with an accuracy of 0.1K with good sensitivity. These NRs may have suitable application for non-contact nano-thermometry. [Preview Abstract] |
Wednesday, March 16, 2016 4:18PM - 4:30PM |
P26.00010: Analysis of metastable ultrasmall titanium oxide clusters using a hybrid global search algorithm and first-principles approach Eric Inclan, Jack Lassester, David Geohegan, Mina Yoon Research in TiO$_{\mathrm{2}}$ materials is highly relevant to energy and device applications, however, precise control of their morphologies and characterization are still a grand challenge in the field. We developed and applied a hybrid optimization algorithm to explore configuration spaces of energetically metastable TiO$_{\mathrm{2}}$. Our approach was to minimize the total energy of TiO$_{\mathrm{2\thinspace }}$clusters in order to identify the energy landscape of plausible (TiO$_{\mathrm{2}})_{\mathrm{n}}$ (n $=$ 1-100). The hybrid algorithm retained good agreement with a regression on structures published in literature up to n $=$ 25. Using first-principles density functional theory, we analyze basic properties of the hybrid-algorithm generated TiO$_{\mathrm{2\thinspace }}$nanoparticles. Our results show the expected convergence to bulk material characteristics as the cluster size increases in that the band gap varies with respect to the size of the nanocluster. The nanoclusters trended toward compact, low surface area structures that share characteristics of the bulk, namely octahedral microstructures as the nanoclusters increased in size. Our study helps in better identifying and characterizing experimentally observed structures. [Preview Abstract] |
Wednesday, March 16, 2016 4:30PM - 4:42PM |
P26.00011: Low energy THz excitations in distorted perovskites under strong magnetic fields and low temperature. N. E. Massa, K. Holldack, V. Ta Phuoc, R. Sopracase, L. del Campo, D. De Sousa Meneses, P. Echegut, J.A. Alonso We report on the magnetic field evolution of distinctive absorption bands in several zero field cooled polycrystalline RMO$_{\mathrm{3}}$ (R$=$ Pr, Nd, Sm, Er, Tm, Lu; M$=$ Cr, Mn, Fe. Ni) at low temperatures. Measurements below 120 cm$^{\mathrm{-1}}$ were done in an 11 T magnet combined with a Bruker IFS125-HR interferometer at the THz beamline of the BESSY II storage ring. At the reordering spin temperature, the spectra of ErCrO$_{\mathrm{3}}$ show an Er-Kramers doublet at \textasciitilde 55 cm$^{\mathrm{-1}}$ following a second order continuous reorientation. It suggests strong anisotropic Er$^{\mathrm{3+}}$-Cr$^{\mathrm{3+\thinspace }}$magnetic exchange interactions. The band strength of its triplet excited states decreases upon increasing the magnetic field. Non-Kramers Pr in PrCrO$_{\mathrm{3}}$ implies a magnetic field induced quasi-doublet system. Spin wave modes AF and F are also tentatively assigned. In ErFeO$_{\mathrm{3}}$, the spin reordering of the canted transition metal, and the Er$^{\mathrm{3+}}$ exchange, is monitored emerging above 80 K. Temperature dependent multiplet transitions centered at 50 cm$^{\mathrm{-1}}$ and 110 cm$^{\mathrm{-1}}$ appear as asymmetric field dependent broad lines. The absence of activity at \textasciitilde 4 K in SmCrO$_{\mathrm{3}}$, shared by SmMO$_{\mathrm{3\thinspace }}$(M$=$Fe, Ni), is consequence of near Cr-canted-Rare-Earth-opposite moment compensation juxtaposed to random micrograin orientation. We will also comment on observed only in ErNiO$_{\mathrm{3}}$ field dependent Er transitions and band profiles. [Preview Abstract] |
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