Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session T33: Focus Session: Dielectric, Ferroelectric, and Piezoelectric Oxides: Pb-based and novel materials |
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Sponsoring Units: DMP DCOMP Chair: Xiaoqing Pan, University of Michigan Room: C143/149 |
Wednesday, March 23, 2011 2:30PM - 3:06PM |
T33.00001: Origin of diffuse scattering in relaxor ferroelectrics Invited Speaker: High-pressure and variable temperature single crystal synchrotron X-ray measurements combined with first-principles based molecular dynamics simulations study diffuse scattering in the relaxor ferroelectric system PSN (PbSc1/2Nb1/2O3). Constant temperature experiments show pressure induced transition to the relaxor phase at different temperatures characterized by butterfly and rod shaped diffuse scattering around the {\{}h00{\}} and {\{}hh0{\}} Bragg spots, respectively. The simulations [1] reproduce the observed diffuse scattering features as well as their pressure-temperature behavior, and show that they arise from polarization correlations between chemically-ordered regions, which in previous simulations were shown to behave as polar nanoregions. Simulations also exhibit radial diffuse scattering (elongated towards and away from Q=(000)), that persists even in the paraelectric phase, consistent with previous neutron experiments on (PbMg1/3Nb2/3O3) (PMN). DFPT calculations to elucidate origin of Raman peaks in the relaxor phase will also be presented. \\[4pt] [1] P. Ganesh, E. Cockayne, M. Ahart, R. E. Cohen, B. Burton, Russell J. Hemley, Yang Ren, Wange Yang and Z.-G. Ye, Phys. Rev. B \textbf{81}, 144102 (2010) [Preview Abstract] |
Wednesday, March 23, 2011 3:06PM - 3:18PM |
T33.00002: Linear dichroism dependence on ferroelectric polarization Srinivas Polisetty, Jinling Zhou, Mikel Holcomb, Andreas Scholl, Lane W. Martin X-ray absorption spectroscopy (XAS) and photoemission electron microscopy (PEEM) have been used to determine the magnetic properties of magnetoelectrics, possessing both ferroelectric and magnetic order; however, the additional sensitivity to the ferroelectricity in these films complicates the analysis. Nevertheless, an exclusive knowledge of ferroelectric order is important due to its vital role in manipulating magnetic properties of the magnetoelectrics. To shed light on ferroelectric order and polarization near surface region, we employed mainly PEEM and XAS on ferroelectric PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$ (PZT) film deposited on LaAlO$_{3}$ substrate. Both out-of-plane and in-plane ferroelectric contributions at Ti $L_{3,2}$ and O-absorption edges have been measured over multiple poled regions on the sample to test various potential mechanisms causing this ferroelectric dichroism, such as surface charge. The ferroelectric order in PZT determined to be systematically evolving as a function of incident x-ray polarization for different rotated angles of the sample revealing a similar angular dependence to that of magnetic samples, allowing a formula for linear dichroism in complex ferroelectrics. This development allows this dynamic approach to be used to study the effect of ferroelectricity on interface coupling in a various materials. [Preview Abstract] |
Wednesday, March 23, 2011 3:18PM - 3:30PM |
T33.00003: Second harmonic generation and high pressure ferroelectricity in PbTiO$_{3 }$(II) Muhtar Ahart, Alexander F. Goncharov, Maddury Somayazulu, Russell J. Hemley We employed the Raman scattering, x-ray diffraction, and second harmonic generation (SHG) experiments to investigate the behavior of PbTiO$_{3}$ under pressure up to 100 GPa at 300 K. The experimental results reveal that lead titanate undergoes a second order phase transition from a tetragonal to a cubic at 12 GPa and continuously to a non-cubic structure at 30 GPa. The integral intensity of SHG in the material decreases monotonically with pressure below 12 GPa, and does not depend on pressure above 12 GPa. The results provide no-evidence for high pressure ferroelectricity in PbTiO$_{3}$ at high pressure and room temperature. [Preview Abstract] |
Wednesday, March 23, 2011 3:30PM - 3:42PM |
T33.00004: First-principles study to identify heterostructures of (Pb, Sr)TiO$_{3}$ with enhanced ferroelectric polarisation Zhe Liu A first-principle cluster expansion method is employed to study the ferroelectric (FE) polarisation properties of Pb$_{x}$Sr$_{1-x}$TiO$_{3}$ perovskite oxide grown on SrTiO$_{3}$ (001)-substrate. Our results indicate that some heterostructures can significantly enhance polarisation in comparison with the (001) superlattice and the random alloy structures. At $x=0.5$, an (110) A/B mono-layer superlattice is identified as the structure with the most enhanced polarisation, and at $x=0.25$, the optimal structure is determined to be a body-centred superstructure. Detailed structural analysis reveals the atomic configurational patterns in the (001) plane that benefit the off-centering of Pb and Sr cations. Explanation is provided in terms of dipole interactions. Our results should apply to other multicomponent FE perovskites as well and they could have a significant impact in the design of FE materials. [Preview Abstract] |
Wednesday, March 23, 2011 3:42PM - 3:54PM |
T33.00005: Interatomic force constants and effective Hamiltonians for structural phase transitions Anil Kumar, Karin M. Rabe Expansion of the total energy of a crystal around a high-symmetry reference structure provides information about material properties including the phonon dispersion, responses to applied fields, magnetostructural coupling, and structural transitions. For complex oxides, parameterization of the structural energetics by real-space interatomic force constants (IFCs) provides a computationally convenient and physically transparent way of analyzing these properties. By projection into a subspace containing the relevant degrees of freedom, one can construct an effective Hamiltonian to study properties that are not readily accessible with DFT based calculations, including properties at finite temperature or long length scales. It is well known that first-principles density-functional-theory (DFT) based-calculations can be systematically used to determine real-space IFCs of materials; this is part of several first-principles packages including ABINIT and Quantum Espresso. Here, we discuss a simple and efficient approach for construction of first-principles effective Hamiltonians which uses this computational capability to generate and compute the quadratic inter-cell parameters in a single step. We illustrate the method through the application to systems for which effective Hamiltonians have previously been constructed, and show how this approach facilitates the construction of effective Hamiltonians for new classes of crystal structures. [Preview Abstract] |
Wednesday, March 23, 2011 3:54PM - 4:06PM |
T33.00006: All-atom effective models for first-principles simulations of the temperature-dependent behavior of complex ferroelectric oxides Jorge Iniguez, Jacek C. Wojdel, Patrick Hermet, Philippe Ghosez, Zeila Zanolli Since its introduction in the 90's, the first-principles effective-Hamiltonian method has been successfully used to simulate temperature-driven phenomena in increasingly complex ferroelectrics, from classic compound BaTiO$_3$ to multiferroic BiFeO$_3$. Currently, the emergence of nano-structured materials -- e.g., in the form of ultra-thin films or short-period superlattices -- poses new challenges to the simulations, and the development of predictive models seems to require a reconsideration of the traditional approach. Of particular interest are cases in which novel interfacial effects determine the behavior, as in the PbTiO$_3$-SrTiO$_3$ superlattices of Bousquet {\sl et al}. [Nature {\bf 452}, 7188 (2008)]. In such situations a large number of structural distortions may become active, and it may be difficult to decide which ones need to be included in the model. In order to tackle these difficulties, we are extending the first-principles effective-Hamiltonian method so as to retain a full atomistic description of the material, thus removing the so-called {\em local mode} approximation. I will describe our new approach and show preliminary results for PbTiO$_3$. [Preview Abstract] |
Wednesday, March 23, 2011 4:06PM - 4:18PM |
T33.00007: Prediction of a Low Band Gap Oxide Ferroelectric David Singh, Bo Xu, Valentino R. Cooper, Yuan Ping Feng We report a first principles study of Bi$_6$Ti$_4$O$_{17}$ which is an alternate stacking of ferroelectric Bi$_4$Ti$_3$O$_{12}$ (BiT). We the standard PBE GGA functional for the structure and polarization and a recently developed functional that yields accurate band gaps for the electronic structure. We find that this compound is ferroelectric although with a reduced polarization relative to BiT. Importantly, calculations of the electronic structure yield a band gap of approximately 1.4 eV. Therefore, we predict that this stacking is a low band gap oxide ferroelectric. [Preview Abstract] |
Wednesday, March 23, 2011 4:18PM - 4:30PM |
T33.00008: Band Gap Engineering via Local Environment in Complex Oxides Tingting Qi, Ilya Grinberg, Andrew Rappe We describe how the electronic structure energy level of the recently-developed highly polar tetragonal perovskite oxides, most prominently Bi(Zn,Ti)O$_3$, can be dramatically changed by a simple rearrangement of the $B$-cation. Using LDA+Hubbard $U$, we determine the impact of $B$-site cation ordering, lattice strain, cation identity, and oxygen octahedral cage tilts on the valence and conduction bands. We find that a combination of ultra-high tetragonality and a careful choice of $B$-cations can lead to changes of 1-2 eV in the band gap for the same composition, through a change in the $B$-cation ordering alone. We also find that a layered $B$-cation ordering exhibits high-mobility 2D hole gas (2DHG) behavior. The lower band gaps of the layered $B$-cation ordering makes these materials suitable for photovoltaic and photocatalytic applications, due to their good match with the solar spectrum. Our analysis of the crystal structure and the valence and conduction bands shows that these unusual effects can be explained in the framework of crystal field theory and underscores the crucial role that ultra-high tetragonality plays in making the band gap sensitive to the $B$-cation ordering. [Preview Abstract] |
Wednesday, March 23, 2011 4:30PM - 4:42PM |
T33.00009: Modeling the Frequency Dependence of the Complex In-plane Permittivity of Strained Ruddlesden-Popper Series Sr(n+1)Ti(n)O(3n+1) (n = 2, 3, 4, 5, 6) Phases on DyScO3 and GdScO3 N.D. Orloff, C.-H. Lee, M.D. Biegalski, Ichiro Takeuchi, D.G. Schlom, J.C. Booth We explore the in-plane complex relative permittivity as a function of frequency of epitaxial thin-films of the Ruddlesden-Popper series Srn+1TinO3n+1 (n = 2, 3, 4, 5, 6) grown on the rare-earth scandate substrates DyScO3 and GdScO3, which correspond to biaxial tensile strain of approximately 1.1{\%} and 1.7{\%}, respectively. The thin films are 50 nm on DyScO3 and 25 nm thick on GdScO3, to ensure uniform strain throughout the film. We characterize the thin films with a set of optimally designed coplanar waveguides from 45 MHz to 40 GHz and with a set of interdigitated electrodes of varying active lengths from 10 Hz to 100 MHz. We then extract the in-plane complex permittivity from 10 Hz to 40 GHz for these thin films. We report the dependence of the Curie temperature, tunability, and loss tangent on series number and strain at 1 MHz. We also present a frequency-dependent model and the corresponding fit parameters for these thin films as a function of temperature. The model assumes a distribution of domains below the Curie temperature and high frequency relaxation that we attribute to the lowest-order phonon [Preview Abstract] |
Wednesday, March 23, 2011 4:42PM - 4:54PM |
T33.00010: Study of Temperature-Graded Ferroelectrics Using First-Principle-Based Approaches Qingteng Zhang, Inna Ponomareva Temperature-graded ferroelectrics have attracted a lot of attention in the recent years owing to their many remarkable properties. Here we develop a microscopic approach based on first-principles effective Hamiltonian to simulate temperature-graded ferroelectrics. Accuracy of such approach is confirmed by comparing our computational results for (Ba$_{0.75}$Sr$_{0.25}$)TiO$_3$ alloy with available experimental data. Our computations further reveal: 1) strong anisotropy in polarization response: the polarization offset along the temperature gradient is an order of magnitude smaller than in the perpendicular direction; 2) coexistence of different phases (including low-symmetry phases) in chemically homogeneous regions; 3) rotation of polarization in response to temperature gradient in the unclamped samples. These findings could potentially lead to many novel applications such as energy converters, thermally tunable devices and efficient photovoltaics [1].\\[4pt] [1] Q. Zhang {\it et al}, Phys. Rev. Lett. {\bf 105}, 147602 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 4:54PM - 5:06PM |
T33.00011: Ferroelectric polarizations of Pb(Zr$_{0.5}$Ti$_{0.5}$)O$_3$ nanotube array R. Adhikari, Huaxiang Fu Ferroelectric polarization and structural properties are determined for the Pb(Zr$_{0.5}$Ti$_{0.5}$)O$_3$ (PZT) nanotube array embedded in matrix materials of different polarizability, by means of first-principles derived effective Hamiltonian and finite-temperature Monte Carlo simulations. The polarizability of the matrix is controlled by the on-site $\kappa_2$ quantity. We found three drastically different structural phases in PZT nanotubes, depending on the polarizability of the matrix. Microscopic insight for these structural phases will be revealed. [Preview Abstract] |
Wednesday, March 23, 2011 5:06PM - 5:18PM |
T33.00012: Raman scattering studies of the pressure- and temperature-dependent phases of the orbital ordering material KCuF$_{3}$ Shi Yuan, S. Lance Cooper We present a study of the temperature- and pressure-dependence of the prototypical orbital ordering system KCuF$_{3}$ using Raman scattering. Temperature-dependent measurements offer evidence for structural instabilities in KCuF$_{3}$ at temperatures well below the putative 800K orbital ordering temperature; this evidence includes the observation of anomalous softening of several phonon modes between 50K and 300K and an E$_{g}$ phonon mode splitting below 50K. The latter indicates a tetragonal-to-orthorhombic structural transition near 50K just preceding the 3D magnetic ordering temperature at T$_{N} \quad \approx $ 40K. Low-temperature, pressure-dependent Raman studies of KCuF$_{3}$ are also reported to clarify the pressure dependence of the low temperature structural phases in this material. [Preview Abstract] |
Wednesday, March 23, 2011 5:18PM - 5:30PM |
T33.00013: Unusually strong Stark effect in electronic ferroelectric Er$_{1-x}$Yb$_{x}$Fe$_{2}$O$_{4}$ Jimin Zhao, Rui Wang, Huanxin Yang, Jianqi Li Strong Stark splitting, which is nearly independent of the R-ions replacement, has been observed through the photoluminescence investigation of electronic ferroelectric Er$_{1-x}$Yb$_{x}$Fe$_{2}$O$_{4 }$(x=0, 0.8, 0.9, and 0.95). Initially multiple radiative decay channels have been investigated, especially the visible transition $^{4}F_{9/2}\to ^{4}I_{15/2}$, of which a quenching effect has been observed. A series of small non-Raman peaks have been observed superimposed on a broadband photoluminescence spectrum, of which we tentatively assign Stark splitting to be the cause. The splitting of the $^{4}F_{9/2}$ and $^{4}I_{15/2}$ levels is found to be 54 meV and 66 meV, respectively. This unusually large Stark splitting at visible range indicates the existence of strong local field originated from the W-layer in the charge-frustrated ErFe$_{2}$O$_{4}$. [Preview Abstract] |
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