Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V37a: Dielectric and Ferroelectric Oxides VIIFocus
|
Hide Abstracts |
Sponsoring Units: DMP Chair: Joshua Young, Northwestern University Room: 383 |
Thursday, March 16, 2017 2:30PM - 3:06PM |
V37a.00001: Ferroionic states: coupling between surface electrochemical and bulk ferroelectric functionalities on the nanoscale. Invited Speaker: Sergei Kalinin Ferroelectricity on the nanoscale has remained a subject of much fascination in condensed matter physics for the last several decades. It is well-recognized that stability of the ferroelectric state necessitates effective polarization screening, and hence screening mechanism and screening charge dynamics become strongly coupled to ferroelectric phase stability and domain behavior. Previously, the role of the screening charge in macroscopic ferroelectrics was observed in phenomena such as potential retention above Curie temperature, back switching of ferroelectric domains, and chaos and intermittency during domain switching. In the last several years, multiple reports claiming ferroelectricity in ultrathin ferroelectrics based on formation of remanent polarization states, local hysteresis loops, and pressure induced switching were made. However, similar phenomena were reported for traditionally non-ferroelectric materials, creating significant level of uncertainty in the field. We pose that in the nanoscale systems, the ferroelectric state is fundamentally inseparable from electrochemical state of the surface, leading to emergence of coupled electrochemical-ferroelectric states. I will present the results of experimental and theoretical work exploring the basic mechanisms of emergence of these coupled states including the basic theory and phase-field formulation for domain evolution. I further discuss the thermodynamics and thickness evolution of this state, and demonstrate the experimental pathway to establish its presence based on spectroscopic version of piezoresponse force microscopy. Finally, the role of chemical screening on domain dynamics is explored using phase-field modelling. This analysis reconciles multiple prior studies, and set forward the predictive pathways for new generations of ferroelectric devices and applications. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V37a.00002: The Origin of Uni-axial Negative Thermal Expansion in a Layered Perovskite Chris Ablitt, Sarah Craddock, Mark Senn, Arash Mostofi, Nicholas Bristowe Using first-principles calculations within the quasi-harmonic approximation (QHA), we explain the origin of experimentally observed uni-axial negative thermal expansion (NTE) in a layered perovskite: the Ruddlesden--Popper (RP) oxide Ca$_2$MnO$_4$, which has anti-ferromagnetic ordering at low temperatures and is closely related to Ca$_3$Mn$_2$O$_7$, which exhibits hybrid improper ferroelectricity and uni-axial NTE in competing phases. Dynamic tilts of MnO$_6$ octahedra, common in many complex oxides, drive the expansion of the $a$ axis and contraction of the $c$ axis of the tetragonal NTE phase. We find that ferroelastic RP phases with a frozen octahedral rotation are unusually compliant to particular combinations of strains along different axes. The atomic mechanism responsible is characteristic of the perovskite/rock-salt interfaces present in the RP structure. We show that the contribution from this anisotropic elasticity must be taken into account in order to accurately predict NTE over the temperature range observed in experiment. A similar compliance to cooperative strains is found in other systems with uni-axial NTE. The development of this mechanistic understanding of NTE in complex oxides may pave the way for designing tunable multifunctional materials. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V37a.00003: Pinched hysteresis loop in defect-free ferroelectric materials Bin Xu, Charles Paillard, Laurent Bellaiche, Brahim Dkhil In addition to the single polarization-{\it versus}-electric field hysteresis loop that is characteristic of ferroelectrics and the double hysteresis loop that is known to occur in antiferroelectrics, a third kind of polarization-{\it versus}-electric field function has been reported in several systems. This third kind is commonly termed the ``pinched'' loop due to its unusual shape, and is typically believed to originate from the pinning of domain walls interacting with defects. Here, using an atomistic effective Hamiltonian scheme, we demonstrate that such belief has to be broadened since our simulations also yield pinched loops in defect-free ferroelectric materials, as a result of the occurrence of intermediate modulated phases exhibiting an inhomogeneous dipolar pattern leading to the coexistence of both ferroelectric and antiferroelectric orders [1]. [1] B. Xu \textit{et al.} Phys. Rev. B \textbf{94}, 140101(R) (2016) [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V37a.00004: Domain walls and ferroelectric reversal in corundum derivatives Meng Ye, David Vanderbilt Domain walls are the topological defects that mediate polarization reversal in ferroelectrics, and they may exhibit quite different geometric and electronic structures compared to the bulk. Therefore, a detailed atomic-scale understanding of the static and dynamic properties of domain walls is of pressing interest. In this work, we use first-principles methods to study the structures of $180^{\circ}$ domain walls, both in their relaxed state and along the ferroelectric reversal pathway, in ferroelectrics belonging to the family of corundum derivatives. Our calculations predict their orientation, formation energy, and migration energy, and also identify important couplings between polarization, magnetization, and chirality at the domain walls. Finally, we point out a strong empirical correlation between the height of the domain-wall mediated polarization reversal barrier and the local bonding environment of the mobile $A$ cations as measured by bond valence sums. Our results thus provide both theoretical and empirical guidance to further search for ferroelectric candidates in materials of the corundum derivative family. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V37a.00005: Systematic study of the electronic structure of a doped Mott insulator P Ganesh, J Balachandran, Y Luo, H Shin, A Benali, P.R.C Kent, O Heinonen Controlled manipulation of electronic properties of Mott insulators through doping is an important step towards realizing Mottronics. However, describing the electronic-structure of correlated electronic materials, such as doped Mott insulators, is challenging using conventional density functional theory (DFT) methods. A wide range of methods to correct for this deficiency in DFT has been recently proposed, such as SIC-DFT, DFT$+$U, hybrid-DFT etc. In this talk we will explore the sensitivity of these different methods, in describing the electronic-structure of K-doped NiO, and compare our predictions from these methods with those obtained from a more accurate many-body method, such as quantum monte-carlo (QMC), which accurately describes such correlated electron systems. We will address questions such as: Where are the holes located in K-doped NiO? How localized are they? How does the localization depend on the doping concentration, and affect the conductivity of the material? We will also contrast our results to Li-doped NiO, which has been experimentally studied before. Answers to these questions have serious ramifications to our ability to describe electronic phase transitions in doped solids where strong electron correlations dictate the underlying physics of the material. * This work was supported by the U.S. Department of~Energy, Office of Science, Basic Energy Sciences, Computational Materials Sciences Program. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V37a.00006: A flip-chip test set for complex permittivity measurement of thin-films up to 110 GHz Nathan Orloff, Chris Long, James Booth Complex permittivity measurement can be used to understand underlying physics in complex material systems and to identify potential industrial applications. With the development of new dielectrics sparked by materials-by-design, it has become increasingly important to develop a standardized complex permittivity metrology to test and measure materials. Test of new materials often requires the fabrication of electrodes on the material-under-test. For high frequency, coplanar waveguides are commonly used to measure the complex permittivity, while interdigitated capacitors are used at low frequency. Since many new dielectrics are gown on chips, the size of the material-under-test limits the design of electrodes, the number of devices, and the fabrication techniques. This limits the measurement accuracy and impedes materials discovery. Here, we develop a flip-chip technique for measuring the complex permittivity to 110 GHz. This flip-chip technique uses electrodes fabricated on a 75 mm wafer, a lithographically defined polymer stand-off to control the measurement sensitivity, and a test fixture to hold the material-under-test in place. Successful implementation of this flip-chip approach will allow for the rapid, nondestructive characterization of new materials without the need for chip-based fabrication. [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V37a.00007: Potential Hybrid Improper Ferroelectricity in the Oxyfluoride KNaNbOF$_5$ Jaye Harada, Nenian Charles, Juan Nino, Kenneth Poeppelmeier, James Rondinelli We assess whether the observed displacive transition between a low temperature polar and high temperature centrosymmetric phase of the oxyfluoride KNaNbOF$_{5}$ is proper or improper using a combination of materials theory and experimentation. Although the transition appears to occur at a single critical temperature, crystallographic mode analyses shows that two lattice modes are required to produce the structure of the low-symmetry phase; these facts together suggest an improper character requiring further investigation. First, we experimentally verify the order of the transition using dielectric measurements and differential scanning calorimetry. Then, using density functional theory calculations and phenomenological Landau theory, we determine the relevance of permitted trilinear multimode interactions on the stability of the observed grounds state and the suppression of potential intermediate phases. Based on these simulations, we also discuss the potential for experimental switching of the ferroelectric polarization. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V37a.00008: Structure and Electronic Dependencies on Anion Order in Oxyfluoride Elpasolites Nenian Charles, James Rondinelli Complex oxyfluoride compounds are an emerging class of materials that aim to combine the advantageous properties of oxides and fluorides. Moreover, the ensuing order of the oxide and fluoride anions provides an additional knob to tune properties. However, there remains no complete set of design rules for realizing and controlling anion order in metal oxyfluorides. Here, we investigate the anion site order dependence on cation chemistry in the elpasolite double perovskite oxyfluoride family using group theoretical techniques and density functional theory (DFT) calculations. We enumerate hundreds of anion ordered structural variants with $A_2BM$O$_x$F$_{6-x}$ ($x$ = 1, 2, 3) stoichiometry and develop a classification scheme based on characteristic symmetry adapted mode distortions exhibited within the family of compounds. Using DFT calculations we show that changing the $d$ orbital filling of the $M$ cation can modulate the relative stability among structural variants. Our results advance the understanding of anion order in oxyfluoride compounds and we anticipate that it will guide the synthetic stabilization of new oxyfluorides elpasolites. [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V37a.00009: Directing and harnessing anion order in YBaFe2O5F oxyfluoride perovskites Steven Hartman, Arashdeep Thind, Rohan Mishra Anion ordering in mixed-anion transition metal perovskites, such as oxyfluorides, offers a new route to control their properties and achieve novel functionalities. However, O/F ordering is limited by entropy in oxyfluorides synthesized through traditional solid-state techniques, which require high temperatures. Here, using total energies and activation barriers from first-principles density functional theory calculations, we show that it is possible to achieve O/F order using topochemical fluorination of oxide perovskites having ordered oxygen vacancies. We use YBaFe$_{2}$O$_{5}$ as a representative compound, which has oxygen vacancies that are ordered in the Y-layers. We find that fluorination is most favorable at the oxygen vacancy site in the Y-layers, which leads to polar building units with finite dipole moment due to alternating layers of BaO and YF about the FeO$_{2}$ layers. We will discuss these findings along with the predicted electronic and magnetic properties of YBaFe$_{2}$O$_{5}$ with O/F order. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V37a.00010: Abstract Withdrawn
|
Thursday, March 16, 2017 4:54PM - 5:06PM |
V37a.00011: Efficient Computation of Spontaneous Polarization Using Wannier Center Displacements John Bonini, Oscar Paz, David Vanderbilt, Karin Rabe A widely-used approach to computing the spontaneous polarization of a crystalline ferroelectric is to calculate the Berry-phase polarization for structures along a deformation path between the centrosymmetric and polar structures and use continuity of the polarization to resolve the ambiguity arising from the fact that the polarization of a bulk crystal is only defined modulo a lattice. In this work we formulate an alternative symmetry-based method to obtain the spontaneous polarization {\it using only one self-consistent calculation} by inferring the displacements of Wannier centers between oppositely polarized states. This method gives the same result as the first, while avoiding the inefficiency involved in construction of a deformation path and computation for multiple hypothetical structures. We present applications to a wide variety of ferroelectric structures. In addition, we will discuss how this formulation provides a natural framework for the physics of the switching polarization in more exotic cases, such as charge-ordered ferroelectrics. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V37a.00012: First-principles theory of improper ferroelastic walls Massimiliano Stengel, Andrea Schiaffino Domain walls in ferroic materials are characterized by unique structural and electronic properties that markedly depart from those of the homogeneous crystalline phase. These often enable new functionalities that are forbidden by symmetry in the bulk and are of interest for applications, e.g., in nanoelectronics. Ferroelastic twin walls, in particular, have received considerable attention in the past few years, as they are characterized by a net dipole moment even if the parent material is nonpolar. Several models have been proposed to rationalize this observation, ranging from flexoelectricity to improper ferroelectricity, but a fundamental theory of the effect is still missing. In this talk I will first give a brief overview of the technical and conceptual challenges that one has to face when approaching this problem from the perspective of microscopic electronic-structure theory. Next, by using ferroelastic twins in SrTiO$_3$ as a testcase, I will show how these challenges can be successfully overcome, leading to a physically consistent, quantitatively predictive description of domain wall-induced polarity. Finally, I will discuss practical examples where a twin wall structure can break macroscopic inversion symmetry, and thereby yield a nonvanishing electrical polarization. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700