Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session W24: Focus Session: Dielectric, Ferroelectric, and Piezoelectric Oxides -- Bulk Ferroelectrics II |
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Sponsoring Units: DMP Chair: Serge Nakhmanson, Argonne National Laboratory Room: D133-D134 |
Thursday, March 18, 2010 11:15AM - 11:27AM |
W24.00001: Strain-induced Ferroelectricity in Ruddlesden-Popper Sr(n+1)Ti(n)O(3n+1) Phases N. Orloff, C. Lee, C. Fennie, X. X. Xi, I. Takeuchi, J. C. Booth, D. G. Schlom We performed broadband in-plane dielectric measurements of thin-film Sr(n+1)Ti(n)O(3n+1)(n = 2, 3, 4, 5, 6) Ruddlesden-Popper homologous series as a function of temperature and bias field. The effect of strain on these materials is interesting, because SrTiO3, the n =~$\infty $ series member, exhibits ferroelectricity at room temperature when strained on~DyScO3 substrates. Here, we explore the effect of strain on the dielectric properties of~Sr(n+1)Ti(n)O(3n+1)(n = 2, 3, 4, 5, 6) thin-films on~LSAT, DyScO3 and GdScO3. [Preview Abstract] |
Thursday, March 18, 2010 11:27AM - 11:39AM |
W24.00002: The Optical Bandgap of Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ (\textit{n}=1$\sim $5, 10) Ruddlesden-Popper Phases Chehui Lee, Nikolas Podraza, Xiaoxing Xi, Darrell Schlom The Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ Ruddlesden-Popper homologous series is of particular interest because its n=$\infty $ member SrTiO$_{3}$ exhibits such a wide range of properties including high dielectric constant, tunable dielectric constant, and superconductivity. In this study we explore the optical bandgaps of the Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ ($n$=1$\sim $5, 10) Ruddlesden-Popper phases. This is the first time that a phase-pure $n$=10 Ruddlesden-Popper phase has ever been made. Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ ($n$=1$\sim $5, 10) thin films were grown on (001) LSAT substrates by reactive molecular-beam epitaxy. (001) LSAT substrates provide good lattice match ($<$ 1{\%} mismatch) to the entire Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ series. For the $n$=10 sample, we also deposited it on (001) SrTiO$_{3}$ substrates. SrTiO$_{3}$ substrates provides nearly strain-free growth for the $n$=10 phase. The optical properties of the thin films were studied using \textit{ex situ} spectroscopic ellipsometry. We measured the indirect bandgap of the Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ ($n$=1$\sim $5, 10) Ruddlesden-Popper phases on LSAT and their values decrease monotonically from 3.48 eV ($n$=1) to 3.14 eV ($n=\infty )$ with increasing $n$. The bandgaps of the Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ ($n$=1$\sim $5, 10) Ruddlesden-Popper phases fall between the high bandgap SrO ($n$=0) and SrTiO$_{3}$ ($n=\infty )$ end members of the series. [Preview Abstract] |
Thursday, March 18, 2010 11:39AM - 11:51AM |
W24.00003: Electric field-induced structural transition in rare-earth substituted BiFeO$_3$ from first principles Lucia Palova, Daisuke Kan, Ichiro Takeuchi, Karin M. Rabe Using first principles calculations for BiFeO$_3$, we have identified an orthorhombic Pnma phase, lying only 14 meV per formula unit above the rhombohedral R3c ground state structure, as a low-energy alternative structure. We have constructed a model for the energy landscape in which rare-earth substitution on the Bi site favors the orthorhombic structure, so that it becomes the equilibrium phase about a critical rare-earth concentration (x=0.14 for Sm), resulting in the experimentally-observed morphotropic phase boundary (S. Fujino et al., APL 92, 202904 (2008)). For concentrations slightly above the critical concentration, we interpret the observed antiferroelectric-like double hysteresis loops as being produced by an electric-field-induced transition from the nonpolar orthorhombic phase back to the polar rhombohedral phase. By including the electric-field coupling through a linear $P\cdot E$ term in the energy, we have computed the magnitude and concentration dependence of the critical electric field and estimated the enhancement of the piezoelectric coefficient at the phase boundary, obtaining good agreement with the values obtained from experiment. [Preview Abstract] |
Thursday, March 18, 2010 11:51AM - 12:03PM |
W24.00004: First Principle Based Computation of Pyroelectricity in LiNbO3 Q. Peng, R.E. Cohen Pyroelectricity is of current interest since the discovery of particle acceleration of aqueous ions from changes in temperature at pyroelectric surfaces sufficient to generate hard X-rays[1] as well as neutrons via fusion[2]. We computed the pyroelectric coefficients in LiNbO3 from molecular dynamic simulation with DLPOLY using a shell model potential fitted to Density Functional Theory computations results. The potential was constructed by fitting energies and forces, as well as phonon frequencies and eigenvectors, Born effective charges, and dielectric constants computed from density functional perturbation theory using ABINT. The secondary pyroelectric effect is computed from density functional theory. The spontaneous polarizations were calculated using the Berry phase method. The coefficient of thermal expansivity, elastic moduli, elastic compliances, piezoelectric stress constants and piezoelectric strain constants are computed by linear response and lattice dynamics computations. [1] J. D. Brownridge and S. Raboy, Journal of Applied Physics 86, 640 (1999). [2] B. Naranjo, J. Gimzewski, and S. Putterman, Nature 434, 1115 (2005). [Preview Abstract] |
Thursday, March 18, 2010 12:03PM - 12:15PM |
W24.00005: ABSTRACT WITHDRAWN |
Thursday, March 18, 2010 12:15PM - 12:27PM |
W24.00006: Numerical quantification of the vibronic broadening of the SrTiO$_3$ Ti L-edge spectrum Keith Gilmore, Eric Shirley Calculations of x-ray absorption spectra are typically limited to obtaining the positions and intensities of spectral features, while simply adding broadening artificially to match experimental results. However, spectral widths hold valuable information on the coupling of the notional excited electronic state with the environment. The $2p^{5}3d^{1}$ excited state of the Ti$^{4+}$ ion in SrTiO$_{3}$ experiences Jahn-Teller coupling to e$_{\rm g}$ distortions of the oxygen cage. Such coupling broadens the electronic transition by involving a variable number of e$_{\rm g}$ phonons. We quantify this broadening effect by solving a model Hamiltonian, taking parameters for the Hamiltonian from first-principles calculations. Comparison of numerical and experimental results indicates that this vibronic coupling accounts for the majority of the broadening observed for the L$_3$-edge, but only a minority of the L$_2$-edge spectral width. [Preview Abstract] |
Thursday, March 18, 2010 12:27PM - 12:39PM |
W24.00007: Anisotropic Optical Behavior of Ferroelectric Bismuth Titanate: A Comparison of Experiment and Theory Amritendu Roy, Rajendra Prasad, Sushil Auluck, Ashish Garg Optical properties of bismuth titanate (Bi4Ti3O12 or BiT) are of technological interest as its band gap lies in the visible region. Here we compare the results of theoretical and experimental studies conducted on pure bismuth titanate single crystals. Highly oriented BiT single crystals were synthesized using flux growth method. Spectroscopic ellipsometry measurements were made between 300 to 800 nm for different sample orientations. To obtain the absorption coefficient near the band edge, optical transmission measurements were also made. The refractive index data was fitted to a two-term Sellmeier formula. We also calculated the optical constants for both ferroelectric and paraelectric phases of bismuth titanate using density functional theory as implemented in the Vienna ab-initio simulation package (VASP) in conjunction with projector augmented wave method (PAW). Our calculations show the anisotropy of the optical properties for the electric field parallel and perpendicular to the c-axis of the crystal. Our calculations are in good agreement with the experimental data. [Preview Abstract] |
Thursday, March 18, 2010 12:39PM - 12:51PM |
W24.00008: Dielectric properties of the $Ba Ti O_3 - Bi (Zn_{\frac{1}{2}} Ti_{\frac{1}{2}}) 0_3$ solid solution from density-functional theory Dennis Jackson, David Roundy Using density functional theory combined with the modern theory of polarization, we predict dielectric properties of $Ba Ti O_3$ and $Bi (Zn_{\frac{1}{2}} Ti_{\frac{1}{2}}) 0_3$ in solid solution. In particular, we study the effects of disorder on the system in the presence of a homogeneous finite electric field. We consider all unique configurations of the solid solution in a given supercell, computing the polarization resulting from a given applied field. This provides a statistical ensemble from which we predict the finite-temperature dielectric response. We will discuss the implications for uniform bulk solids and within polar nano-regions of a non-uniform solid. [Preview Abstract] |
Thursday, March 18, 2010 12:51PM - 1:03PM |
W24.00009: Band structure of SrTiO3 with structural phase transition by using ARPES Young Jun Chang, Aaron Bostwick, Yong Su Kim, Karsten Horn, Eli Rotenberg SrTiO3 has been widely investigated for its promising properties in the forms of bulk crystals and thin films. Since Mattheiss predicted the conduction band structure of SrTiO3 with the threefold degenerate Ti 3d bands and its change along the cubic-to-tetragonal phase transition in 1972, there have been many of experimental and theoretical efforts. However, direct measurement of the conduction band structure along the phase transition is not yet achieved. In this talk we present the conduction band structure of SrTiO3 (001) with its temperature dependence by using synchrotron based angle-resolved photoemission spectroscopy (ARPES) measurements. We discuss the shape of the conduction bands and many-body effects. [Preview Abstract] |
Thursday, March 18, 2010 1:03PM - 1:15PM |
W24.00010: Neutron Scattering Study of Single Crystal PZT Daniel Phelan, Peter Gehring, Zuo-Guang Ye, Xifa Long Single crystal specimens of the technologically important ferroelectric material Pb(Zr$_{1-x}$Ti$_{x})$O$_{3}$, or PZT, have only recently been grown for the first time at Simon Fraser University$.$ We have characterized the transition temperatures, thermal expansion, and crystal structure of a PZT single crystal between 10 K and 670 K using neutron scattering methods. This crystal, which has a composition (x$\sim $0.46) that lies close to the morphotropic phase boundary (MPB), exhibits a surprisingly large thermal expansion ($\sim $ 10$^{-3}$ 1/K) that changes sign near 545 K, and a rhombohedral crystal structure at 30 K. In addition we observe an enormous relief of extinction beginning around 650 K, which was observed through the temperature dependence of the (200) Bragg peak. Neutron inelastic measurements are planned as are measurements under an applied electric field. This work was supported by the U. S. Office of Naval Research (Grant No. N00014-1-06-0166). All neutron measurements were performed at the NIST Center for Neutron Research. [Preview Abstract] |
Thursday, March 18, 2010 1:15PM - 1:27PM |
W24.00011: Room Temperature Monoclinic Phase in BaTiO$_{3}$ Single Crystals Sava Denev, Amit Kumar, Andrew Barnes, Eftihia Vlahos, Gabriella Shepard, Venkatraman Gopalan BaTiO$_{3}$ is a well studied ferroelectric material for the last half century. It is well known to show phase transitions to tetragonal, orthorhombic and rhombohedral phases upon cooling. Yet, some old and some recent studies have argued that all these phases co-exist with a second phase with monoclinic distortion. Using optical second harmonic generation (SHG) at room temperature we directly present evidence for such monoclininc phase co-existing with tetragonal phase at room temperature. We observe domains with the expected tetragonal symmetry exhibiting 90$^\circ$ and 180$^\circ$ domain walls. However, at points of higher stress at the tips of the interpenetrating tetragonal domains we observe a well pronounced metastable ``staircase pattern'' with a micron-scale fine structure. Polarization studies show that this phase can be explained only by monoclinic symmetry. This phase is very sensitive to external perturbations such as temperature and fields, hence stabilizing this phase at room temperature could lead to large properties' tunability. [Preview Abstract] |
Thursday, March 18, 2010 1:27PM - 1:39PM |
W24.00012: Surface electronic structure of positively and negatively poled single crystal lithium niobate after surface processes Yang Sun, Woochul Yang, Gary Hembree, Robert Nemanich This study focuses on the surface electronic structure of positive and negative domains of single crystals of lithium niobate. The surface is prepared by solvents cleaning, plasma and annealing process. Positively and negatively poled lithium niobate is cleaned by organic solvents followed by remote plasma exposure. XPS and PEEM are employed to characterize the change of the electronic structure. XPS show the O 1s and Nb 3d peaks shifted to higher binding energy after the plasma. Subsequent annealing to 200C results in the peaks at the initial binding energy. Also, PEEM images of polarity patterned surfaces display contrast between the domains that varies with the different surface treatments. After O-plasma exposure the negative domain is brighter than positive domain in the PEEM image. However, the domain contrast disappears and the overall emission intensity is reduced after annealing at 200C. These results indicate that the photo threshold of the domains is different after the surface treatments. Our results are discussed in terms of modification of the surface electronic structures by band bending and screening. [Preview Abstract] |
Thursday, March 18, 2010 1:39PM - 1:51PM |
W24.00013: Effect of Stoichiometry and Absorption on Self-Pumped Two-Beam Coupling Gain and Photovoltaic Fields in LiNbO$_{3}$:Fe Hans Banerjee, Gary Cook, Partha Banerjee, Sergey Basun, Jennifer Carns, Barry Wechsler, Michael Scripsick, Dean Evans The variation of self-pumped two-beam coupling gain in LiNbO$_3$:Fe crystals is investigated, using a CW Verdi 532 nm laser, as a function of absorption coefficients, $\alpha $, and stoichiometry. The 81 crystals tested contain either 0.02{\%} or 0.05{\%} Fe concentrations and are either stoichiometric, intermediate, congruent, or Li deficient. These compositions include a range of $\alpha $ varying between 0.1 and 16 cm$^{-1}$. Experimental coupling efficiency results exhibit a dependence on both composition and $\alpha $; these parameters influence the photovoltaic field, which plays a large role in coupling efficiencies. Experimental results are compared with a mathematical model using a focused geometry, and values for the photovoltaic fields as a function of composition are extracted. [Preview Abstract] |
Thursday, March 18, 2010 1:51PM - 2:03PM |
W24.00014: Photovoltaic effect in Ferroelectric Materials Rajesh K. Katiyar, Neeraj Panwar, G. Morell, Ram S. Katiyar Photovoltaic effect in ferroelectric materials is of much interest due to the anomalously large open circuit photovoltages when illuminated. It is concluded that this unprecedented high value of photovoltaic effect is due to the presence of non-centrosymmetry in the ferroelectric materials which gives rise to electron excitation, relaxation, and scattering processes. The photovoltaic efficiencies are, however, limited due to small current densities and the large band gap values of the ferroelectric materials. We have synthesized thin films of BiFeO$_{3}$ (a low band gap material $\sim $2.67eV) and ferroelectric material SrBi$_{2}$Ta$_{2}$O$_{9}$(SBT) on silicon substrates with ITO as the bottom electrode. The band gap of the SBT has been decreased by incorporating metallic particles Ag, Pt. in the ferroelectric matrix. The results will be presented. [Preview Abstract] |
Thursday, March 18, 2010 2:03PM - 2:15PM |
W24.00015: X-Ray diffraction analysis of B-site diploe-like substitutions in Barium Titanate Thomas Mion, Steven Tidrow An investigation of phase transitions in dipole like B-site substituted perovskites is reported. Several doped Barium Titanite materials were examined over a temperature range of 173 k to1200 K. Their structural changes were examined by X-Ray diffraction as a function of temperature. Several phase transitions of the doped Barium Titanate have noted and characterized. This material is based upon work supported by, or in part by, the U.S. Army Research Laboratory and the U.S. Army Research Office under contract/grant number W911NF-08-1-0353. [Preview Abstract] |
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