Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F09: Dielectric and Ferroic Oxides - New MaterialsFocus
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Sponsoring Units: DMP Chair: Wei Ren, Shanghai University Room: LACC 301A |
Tuesday, March 6, 2018 11:15AM - 11:51AM |
F09.00001: Improper Ferroelectricity in Stuffed Aluminate Sodalites for Pyroelectric Energy Harvesting Invited Speaker: Hiroki Taniguchi Pyroelectric materials can generate electric energy from temporal variation of temperature. Since the pyroelectric energy harvesting is complementary to thermoelectric one that converts spatial temperature gradient to the electric energy, their combination may boost efficient reuse of waste heat. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F09.00002: Structure and Properties Impacting Ferroelectricity in Sn2P2S6 Sizhan Liu, Han Zhang, Sanjit Ghose, Dean Evans, Roger Lalancette, Trevor Tyson Sn2P2S6 samples prepare under various conditions including chemical vapor transport and the Bridgman method exhibit marked variations in optical and dielectric properties. To understand the origin of these changes, detailed measurements of the thermal properties by specific heat methods are combined with structural measurements on multiple length scales. We link critical temperature-dependent structural changes with enhanced electronic properties. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F09.00003: DFT Density Errors in Vanadium Dioxide Analyzed by Quantum Monte Carlo Ilkka Kylänpää, Janakiraman Balachandran, Panchapakesan Ganesh, Olle Heinonen, Paul Kent, Jaron Krogel Correlated materials such as VO2 are a challenge for current generation density functionals to model accurately. We use diffusion Monte Carlo to provide benchmark total energies and spin densities in VO2 which are fundamental to an accurate description of phase stability and magnetism. We evaluate local, semi-local, meta-GGA, hybrid, and Hubbard-corrected functionals against these benchmarks similar to Medvedev et al. [Science 355, 49 (2017)]. We also find that the best energetic description of the structural phases does not correspond to the most accurate density. However, we do find that an accurate spin density relates to a correct energetic ordering of magnetic states in VO2, though local, semilocal, and meta-GGA functionals partially demagnetize the V sites. The SCAN functional stands out as retaining a near balance of magnetization across the M1-R transition while correctly identifying the ground state crystal structure. In addition to ranking current density functionals, our reference energies and densities serve as important benchmarks for future functional development. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F09.00004: Intrinsic Origin of Enhancement of Ferroelectricity in SnTe Thin Films Kai Liu, Jinlian Lu, Silvia Picozzi, Laurent Bellaiche, Hongjun Xiang Understanding the ferroelectricity in thin films is a fundamental issue for several decades. Previous studies show that ferroelectricity is usually suppressed in a thin film: as the film becomes thinner, ferroelectric transition temperature (Tc) and ferroelectric polarization will decrease. Interestingly and surprisingly, a recent experiment showed that atomic-thick SnTe films have a higher Tc than bulk SnTe. Here, we perform first-principles calculations to investigate the intrinsic origin of such an unusual behavior. We find that the energy barrier for the polarization switching in SnTe thin-films are higher than that in bulk SnTe, and 5-UC SnTe thin-film has the largest energy barrier. This unusual phenomenal is attributed to the interplay between hybridization interactions which are essential for stabilizing ferroelectricity and Pauli repulsions that can suppress ferroelectricity: The increase of barrier with thinner film thickness is due to the fact that the surface Sn atom has weaker Pauli repulsions and thus a smaller force constant than the inner Sn atoms; The decrease of barrier from 5-UC to 1-UC arise from the fact that the HIs decrease with the decrement of film thickness for very thin films. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F09.00005: Investigation of the local polarization switching behavior in La-doped HfO2 structures Pratyush Buragohain, Tony Schenk, Uwe Schroeder, Alexei Gruverman The discovery of ferroelectricity in hafnium oxide (HfO2) based thin films is a promising step towards the realization of ferroelectric based memory devices due to their inherent advantages over conventional perovskite materials, especially their compatibility with existing CMOS technology. Although several studies have reported the integral behavior of the capacitors, an in-depth investigation of the local ferroelectric characteristics has not yet been performed. Here, we will discuss the wake-up behavior and the polarization switching dynamics in ultrathin La-doped HfO2 capacitors investigated by means of Piezoresponse Force Microscopy (PFM). Evolution of the domain structure as a function of the applied voltage confirmed that de-pinning of domains is responsible for the increase in polarization upon field cycling. Step-by-step switching of the polarization coupled with PFM imaging revealed that the domains grow from grain boundaries or pinned domains, if present, following the nucleation limited switching (NLS) model. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F09.00006: Octahedral Rotations Driven by Anion Order in Ruddlesden-Popper Oxyfluorides Jaye Harada, James Rondinelli Although most inorganic heteoranioinc materials exhibit locally polar MO6-mFm polyhedra with ordered ligands, the factors which govern the long-range orientational of these units and their connectivity into three-dimensional structures remains to be quantitatively assessed. Here we use density functional theory calculations and symmetry analyses to study the influence of covalent bonding and long-range and short-range electrostatic interactions on the cooperative structural distortions found in n=1 Ruddlesden-Popper type oxyfluorides. We show that the sense and magnitude of the octahedral rotations in these compounds depend on the ordering of oxide and fluoride ions on the anion sublattice and can be controlled through cation chemistry. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F09.00007: Diffusion Monte Carlo study of defects in Hafnia Raghuveer Chimata, Hyeondeok Shin, Anouar Benali, Olle Heinonen Recent years have seen an increased interest in understanding the electronic properties of Hafnia (HfO2) for its industrial applications in optical coating, high-k dielectrics, as well as potential applications in resistive random access memories (RRAMs). A fundamental problem affecting HfO2 transistors performance is the leakage current near the gate dielectric. This is understood to be related to defects, such as oxygen vacancies, in hafnia. Oxygen vacancies are also understood to profoundly affect resistive switching characteristics of hafnia. In order to elucidate the role of defects, we used Density Functional Theory (DFT) and Diffusion Monte Carlo (DMC) to study the energetics of vacancy/defect creation in cubic hafnia and their effect on the band structure gap of the material. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F09.00008: Structure of A3B2O7 Improper Ferroelectrics Trevor Tyson, Sizhan Liu, Han Zhang, Sanjit Ghose, Jaewook Kim, Sang-Wook Cheong The nature of the onset of ferroelectricity in improper ferroelectric layered A3B2O7 perovskites is being investigated theoretically. To place constraints on the theoretical work, detailed structural measurements are required. In this work we report experimental results from multiple probes of the structure on different length scales and compare them to theoretical predictions. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F09.00009: Use of Equivalent Metamaterial Parameters in Finite Element Models of Macro-scale Metamaterial Dragoslav Grbovic, Fabio Alves, Richard Mattish Experimentally measured reflectance and transmittance are used to obtain effective permittivity, permeability and conductivity for a planar microwave metamaterial. These parameters are then used in a finite element models of macro-scale metamaterial objects, where the metamaterial is represented as a homogeneous layer with frequency-dependent permittivity, permeability and conductivity. We demonstrate good agreement between reflectance and absorbance of metamaterial structure and those obtained from modeling homogenized, macro-scale metamaterials. We further demonstrate use of the method for geometrically scaled, oddly-shaped macroscopic objects. This method significantly reduces computation requirements and enables modeling of metamaterial-made, large area objects without modeling their actual intricate metamaterial structure. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F09.00010: Quantum Monte Carlo Study of Electronic and Structural properties of Hafnia Polymorphs Hyeondeok Shin, Emily Crabb, Anouar Benali, Olle Heinonen We have used Diffusion Monte Carlo (DMC) to study the structural and electronic properties of HfO2 polymorphs. Hafnia has received a great deal of attention due to its wide range of application in industrial devices, such as optical coating, high-k dielectrics, and resistive random access memory (RRAM). Through X-ray diffraction measurement, three different polymorphs of hafnia were reported at low pressure, however, their electronic and structural properties are still not well understood because standard Density Functional Theory (DFT) approaches do not work well, and there is a scarcity of experimental data. Based on recent success using DMC in providing accurate electronic properties for zirconia polymorphs[1] (electronic structure similar to hafnia), we investigated detailed electronic properties of the cubic, tetragonal, and monoclinic phase of hafnia. In addition to DMC, we benchmarked DFT using various hybrid exchange-correlation functionals and used the best results to go beyond what DMC allows in terms of band structures and projected densities of state. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F09.00011: Phase stability and optical properties of Y-doped HfO2 from first principles Yubo Qi, Karin Rabe Hafnia (HfO2), as a high-k material in its tetragonal and cubic phases, has long been recognized as valuable in complementary metal-oxide-semiconductor applications. The discovery of ferroelectricity in HfO2 thin films, with a Pbc21 orthorhombic phase, has been the subject of much recent theoretical and experimental research. One path to stabilizing the ferroelectric phase is through the incorporation of various dopants. Here, we use first-principles methods to explore how Y doping, both with and without associated oxygen vacancies, affects the stability of various candidate HfO2 structures. In addition, we investigate the effects of the dopants and vacancies on the electronic structure and optical properties, which are key to making connections with experimental results and are highly relevant to the possible incorporation of ferroelectric HfO2 into a variety of devices. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F09.00012: Structural Symmetry of LuFe2O4 Sizhan Liu, Han Zhang, Sanjit Ghose, Thomas Emge, Sang-Wook Cheong, Yu-Sheng Chen, Roger Lalancette, Trevor Tyson The LuFe2O4 system has been studied intensively as a novel material with charge ordered driven ferroelectricity. The structural symmetry is critical to understanding the properties of this material. High resolution single crystal XRD and PDF measurements are being used to determine the long range and local structure. A discussion of discussion of the average structure on different length scales will be given. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F09.00013: Infrared Spectroscopy of (In,Nb) co-doped TiO2 David Crandles, Susan Yee The infrared reflectance of ceramic samples of TiO2 and 5 and 10 percent (In,Nb) co-doped TiO2 has been measured between 50 and 8000 cm-1 for various temperatures between 4 and 300 K. Kramers Kronig derived optical conductivity spectra reveal four defect related modes at frequencies that are close to the Raman frequencies of rutile. Co-doping produces a significant loss in the partial spectral weight between 75 and 350 cm-1 which is the spectral range associated with the lowest frequency transverse optical mode (the mode that softens significantly with decreasing temperature). The loss in spectral weight is of the same order of magnitude as the mid-infrared spectral weight observed in transmission measurements of reduced rutile and which has previously been identified with small polaron absorption. |
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