Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A21: Focus Session: New Ferroelectrics and Ferroelectric Mechanisms |
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Sponsoring Units: DMP Chair: Eric Bousquet, Universite de Liege Room: 323 |
Monday, March 18, 2013 8:00AM - 8:12AM |
A21.00001: Effects of Manganese Addition on Ferroelectric Properties of BaTiO$_3$ : Ab initio Study Ivan Naumov, R.E. Cohen As it is well known, Mn is intensively used to improve the electromechanical properties of perovskite oxides like BaTiO$_{3}$, PbTiO$_{3}$ or PbZr$_{\mathrm{x}}$T$_{\mathrm{1-x}}$O$_{3}$. Despite the interest in Mn as a dopant, it is currently poorly understood from the fundamental point of view. Here, we present the results of our ab initio study aimed to elucidate the role of Mn defects and associated with them vacancies on the electronic, atomic and ferroelectric properties of BaTiO$_{3}$. Namely, we discuss the equilibrium geometry and electronic properties of the Mn ions occupying A or B sites and their valence or oxidation states in the presence or absence of an compensated oxygen vacancy. A special attention is given to the formation of dipole moments \textbf{P}$_{\mathrm{d}}$ associated with the dopants and to the interaction between \textbf{P}$_{\mathrm{d}}$ and spontaneous polarization \textbf{P}$_{\mathrm{s}}$. This work is supported by the US Office of Naval Research. [Preview Abstract] |
Monday, March 18, 2013 8:12AM - 8:24AM |
A21.00002: Understanding the role of A-site and B-site cations on piezoelectric instability in lead--free (1-x) BaTiO$_3$ -- xA(Cu$_{1/3}$Nb$_{2/3})$O$_3$ (A $=$ Sr, Ca, Ba) solid solutions Deepam Maurya, Yuan Zhou, Shashank Priya This study provides fundamental understanding of the enhanced piezoelectric instability in lead-free piezoelectric (1-x) BaTiO$_3$-xA(Cu$_{1/3}$Nb$_{2/3})$O$_3$(A: Sr, Ba and Ca and x $=$ 0.0-0.03) solid solutions. These compositions were found to exhibit large longitudinal piezoelectric constant ($d_{33})$ of $\sim$330 pC/N and electromechanical planar coupling constant (\textit{kp}) $\sim$ 46{\%} at room temperature. The X-ray diffraction coupled with atomic pair distribution functions (\textit{PDF})s indicated increase in local polarization. Raman scattering and electron paramagnetic resonance (EPR) analysis revealed that substitutions on A and B-site both substantially perturbed the local octahedral dynamics and resulted in localized nano polar regions with lower symmetry. The presence of nano domains and local structural distortions smears the Curie peak resulting in diffuse order-disorder type phase transitions. The effect of these distortions on the variations in physical property was modeled and analyzed within the context of nanodomains and phase transitions. *spriya@vt.edu [Preview Abstract] |
Monday, March 18, 2013 8:24AM - 8:36AM |
A21.00003: First-principles-based modeling of epitaxial-strain-induced ferroelectricity in CaTiO$_3$ Qibin Zhou, Karin Rabe Epitaxial strain can be used to induce phase transitions from the bulk phase to non-bulk phases in thin films and superlattices. In CaTiO$_3$, it has been previously shown that tensile epitaxial strain induces a transition from the nonpolar bulk orthorhombic phase to a ferroelectric phase. In this study, our first-principles computations revealed that compressive strain also induces ferroelectric phases, one of which has unexpected in-plane polarization. To construct a parametrized energy function that reproduces the properties of CaTiO$_3$ for epitaxial strain over a wide range, I developed an approach in which the parameters in a symmetry expansion are determined by a combination of curve-fitting and constraints to computed first-principles results. This energy function allows the analysis of the competition between the oxygen-octahedron-rotation distortion and the polar mode. The use of this function in modeling the structures and properties of superlattices containing CaTiO$_3$, and in constructing effective Hamiltonian for large scale studies, will be discussed. [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 9:12AM |
A21.00004: Proper, improper and hybrid improper ferroelectricity in oxide perovkites and related compounds Invited Speaker: Philippe Ghosez Ferroelectricity in oxide perovskites and related compounds has been a topic of intensive research for more than 60 years. Recently, the coupling of the ferroelectric mode with other structural distortions has attracted an increasing interest since it offers promising and still widely unexplored possibilities to couple ferroelectricity with other functional properties and even to produce unusual phenomena. In this context, the trilinear coupling between ferroelectric and oxygen rotational modes in naturally occuring and artificial layered perovskites appeared as a practical way to produce unusual dielectric properties or achieve enhanced magneto-electric coupling. Here, I will first briefly reintroduce the concepts of proper, improper and hybrid improper ferroelectricity, highlighting how to rationalize better the concept of improper ferroelectricity. I will contrast the intrinsic behavior of these three classes of compounds in ferroelectric capacitors. Taking then the prototypical example of BiFeO3/LaFeO3 superlattices, I will illustrate how hybrid improper ferroelectricity and trilinear mode coupling is a promising route to potentially achieve electric switching of the magnetization. Finally, considering the case of PbTiO3/SrTiO3 superlattices, I will discuss how to access from first-principles the phase-transition sequence and finite temperature properties of complex systems combining various structural instabilities, which still remains a challenging issue. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:24AM |
A21.00005: Nanoscale design routes to polar oxides Joshua Young, James Rondinelli Many useful material properties, such as ferroelectricity, arise because of inversion symmetry breaking in a material's ground state. Understanding how to purposefully lift spacial parity operations is critical to engineering compounds with `acentric' properties. Using first-principles density functional calculations, we describe the crystal-chemistry criteria necessary to design artificial nanoscale oxides that display spontaneous polarizations using non-polar metal-oxygen polyhedra. By controlling the flavor of A-site cation ordering in AA$^\prime$B$_2$O$_6$ perovskites, we show that spontaneous electric polarizations comparable in magnitude to conventional ferroelectrics are attainable. We conclude by explaining how the criteria can be extended to other material classes to realize polar oxides by design. [Preview Abstract] |
Monday, March 18, 2013 9:24AM - 9:36AM |
A21.00006: Turning ABO$_3$ antiferroelectrics into ferroelectrics: Design rules for practical rotation-driven ferroelectricity in double perovskites and Ruddlesden-Popper compounds Andrew T. Mulder, Nicole A. Benedek, James M. Rondinelli, Craig J. Fennie The discovery of octahedral rotation-induced ferroelectricity has provided a new avenue to realize novel materials to explore the interplay of the electrical polarization and correlated phenomena such as magnetism. Design rules recently established suggest ferroelectricity will exist in layered AA$^{'}$B$_2$O$_6$ perovskites when at least one of the ABO$_3$ constituents forms in the nonpolar Pnma structure. As the majority of perovskites form in Pnma, these rules are widely accessible to many chemistries and therefore have the potential to lead to new classes of multifunctional materials. This recent advance however does not directly address the question of whether or not this polar state is a functional ferroelectric or simply a pyroelectric. In this talk we derive from first principles a chemically and physically intuitive model, based only on the properties of the ABO$_3$ constituents, to guide the realization of both large polarizations and small ferroelectric switching barriers. We show how this model follows from a complex interplay of octahedral rotations, antiferroelectric lattice distortions inherent in every Pnma material, and A-site cation ordering. Finally we demonstrate its applicability not only to the double perovskites but also to Ruddlesden-Popper compounds. [Preview Abstract] |
Monday, March 18, 2013 9:36AM - 9:48AM |
A21.00007: First-principles calculations of epitaxially strained PbZrO$_3$: Coexistence of antiferroelectricity and ferroelectricity Sebastian E. Reyes-Lillo, Karin M. Rabe The antiferroelectric (AFE) - ferroelectric (FE) field-induced transition has important applications in energy-storage capacitors and piezoelectric devices. PbZrO$_3$ is the best known AFE material. Polycrystalline and single crystals PbZrO$_3$ posses a stable AFE ground state below 505 K. In thin films, experimental results show coexistence of antiferroelectricity and ferroelectricity at room and low temperatures. First-principles calculations of epitaxially strained PbZrO$_3$ are carried out to give further evidence of this coexistence and to study the polarization switching path. The space groups of the AFE and FE structures are identified together with their important structural and electrical features. [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:24AM |
A21.00008: New classes of piezoelectrics, ferroelectrics, and antiferroelectrics by first-principles high-throughput materials design Invited Speaker: Joseph Bennett Functional materials, such as piezoelectrics, ferroelectrics, and antiferroelectrics, exhibit large changes with applied fields and stresses. This behavior enables their incorporation into a wide variety of devices in technological fields such as energy conversion/storage and information processing/storage. Discovery of functional materials with improved performance or even new types of responses is thus not only a scientific challenge, but can have major impacts on society. In this talk I will review our efforts to uncover new families of functional materials using a combined crystallographic database/high-throughput first-principles approach. I will describe our work on the design and discovery of thousands of new functional materials, specifically the LiAlSi family as piezoelectrics, the LiGaGe family as ferroelectrics, and the MgSrSi family as antiferroelectrics. [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 10:36AM |
A21.00009: Prediction of ferroelectric order in PbCrO$_3$ Martin Schlipf, Marjana Le\v{z}ai\'{c} In this contribution, we employ density-functional theory (DFT) to analyze the properties of PbCrO$_3$. Experimental observations indicate that PbCrO$_3$ exhibits a semiconducting ground state and crystallizes in a perfect cubic perovskite structure. However, symmetry considerations show that these two properties conflict with each other and as a consequence prior DFT calculations obtained a metallic ground state. Investigating tiltings and Jahn-Teller distortions of the oxygen octahedra with a DFT+$U$ approach, we find a semiconducting ground state in which a polar shift of the ions is energetically favorable. Depending on the size of the Hubbard $U$ parameter, we obtain either a structure with a $P4bm$ or one with a $P4_2mc$ space group. In the $P4bm$ structure, the mechanism driving the polar displacement is analogous to PbVO$_3$. The $P4_2mc$ structure is characterized by a displacive ferroelectic order caused by empty $sp$ orbitals. [Preview Abstract] |
Monday, March 18, 2013 10:36AM - 10:48AM |
A21.00010: Why isn't CsSnF$_3$ ferroelectric? Eva H. Smith, Nicole A. Benedek, Craig J. Fennie Complex fluorides are an interesting class of materials to explore for new ferroelectrics and multiferroics. The elucidation of design rules for new ferroelectric fluorides is challenging because polar fluorides tend to form in structures with a large number of atoms in the unit cell and the ferroelectricity is almost always of the geometric type. In this talk we will discuss our recent attempt to rationally design new polar fluorides from first principles. By exploring the relative stability of the subgroups of the perovskite manifold (using the phonons of the 5-atom cubic structure as a guide), we reveal the origin of ferroelectricity in R3c CsPbF$_3$, the only known polar ABF$_3$ compound. Comparison with CsSrF$_3$, which has a similar tolerance factor but no lone pair cation, reveals that the interplay between lone-pair localization and rotations stabilizes the rotation pattern most compatible with ferroelectricity, $i.e.$, a$^-$a$^-$a$^-$, rather than the more common a$^-$a$^-$c$^+$. Next we replace Pb$^{2+}$ with another lone pair cation, Sn$^{2+}$. Within a perovskite manifold of states CsSnF$_3$ is ferroelectric, yet synthesis of this compound by our experimental collaborators shows that not only isn't it ferroelectric, it isn't even a perovskite. Why? [Preview Abstract] |
Monday, March 18, 2013 10:48AM - 11:00AM |
A21.00011: Why are there so few perovskite ferroelectrics? Nicole Benedek, Craig Fennie Nearly all cubic ABO$_3$ perovskites are unstable to energy-lowering structural distortions, the most common being those that give rise to ferroelectricity (usually an off-centering of the B-site cation) and tilts or rotations of the BO$_6$ octahedra. Whereas there are many perovskites that are either ferroelectric or have rotated octahedra, there are very few perovskites that are both ferroelectric and have rotated octahedra. This observation has lead to the widespread assumption that rotations suppress ferroelectricity and vice versa. Using first-principles density functional theory calculations, in combination with crystal chemistry and symmetry principles, we show that rotations do not always suppress ferroelectricity. In fact, the most fertile place to search for new ferroelectrics may be the place that has thus far been considered the least likely to contain them: materials that are expected to have large rotations. We will show why and how ferroelectricity is suppressed in the most common space group adopted by perovskites (Pnma) and explain how we can use this knowledge to design new ferroelectrics and functional materials. [Preview Abstract] |
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