Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F02: Dielectric & Ferroic Oxides -- Structure, Phase Stability, and Competition IFocus
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Sponsoring Units: DMP DCOMP Chair: Jason Hoffman Room: BCEC 107A |
Tuesday, March 5, 2019 11:15AM - 11:51AM |
F02.00001: Diffuse scattering and the local structure of relaxors Invited Speaker: Daniel Phelan Anomalous dielectric and electromechanical properties make relaxor ferroelectrics fundamentally and technologically appealing. We have used three dimensional diffuse scattering measurements (x-ray and neutron) to investigating several classes of relaxor ferroelectrics, including pseudo-cubic Pb-based perovskites and uniaxial tungsten bronze systems. We discuss the different components that are observed in these measurements and how they relate to the physics and material properties of these systems. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F02.00002: Effects of Substrate Orientations on Phase Stability of Epitaxial HfO2 Thin Films Shi Liu, Brendan Hanrahan The discovery of ferroelectricity in both pure and doped HfO2 thin films have revitalized the interest in using ferroelectrics for nanoscale device applications. Previous studies on epitaxial strain engineering of ferroelectricity have mostly focused on thin films grown on (001)-oriented substrates. There is increasing interest in applying biaxial strain along other crystallographic planes such as (101) and (111) by growing thin films on substrates of different cuts. In this work, we focus on the effects of film orientations on the phase stability of HfO2 thin films. We start by examining the ideal transition barriers between different phases of HfO2 with first-principles methods. We find that the three phases, P21/c, Pca21 , and Pbca are separated by relatively large barriers. We calculate the energetics of different polymorphs of hafnia with epitaxial constraints imposed on the {100}, {110}, and {111} planes. Our calculations suggest that the two orthorhombic phases can become the ground state in (111)-oriented thin films. This work suggests the possibility to better stabilize the ferroelectric phase in HfO2 thin films through substrate orientation engineering. |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F02.00003: Competing phases of HfO2 in applied electric field: A first principles insight Yubo Qi, Karin Rabe The recent discovery of ferroelectricity in doped HfO2 thin films has generated intense experimental and theoretical interest, with a particular focus on the precise nature of the HfO2 ferroelectric phase and the factors promoting the observation of ferroelectric switching. In this talk, I present first principles results and analysis to demonstrate how phases of HfO2 evolve under applied electric field as a function of field magnitude and direction. In particularly, the symmetry breaking of yttrium dopants is shown to open new reaction pathways for structural transformation, leading to an electric-field-driven transition from a metastable nonpolar tetragonal phase to the polar ferroelectric orthorhombic phase. The implications of the results for interpreting recent experimental observations will be discussed. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F02.00004: Unconventional Stability of Subloop Behavior for Neuromorphic Computing in a Ferroelectric HfO2 KyoungJun Lee, Seung Chul Chae Recent discovery of ferroelectricity in HfO2 film has attracted not only as a conventional non-volatile memory application but as a neuromorphic analogue device. Multiple intermediate state in ferroelectric switching is one of good candidate for neuromorphic application. Though ferroelectric HfO2 have CMOS compatibility and ferroelectricity in thin film thickness, due to its large coercive field which can induce uncertainty in multi-level switching process, multilevel switching process research is needed. |
Tuesday, March 5, 2019 12:27PM - 1:03PM |
F02.00005: Pyroelectric Energy Conversion with Relaxor Ferroelectric Thin Films Invited Speaker: Lane Martin The need for efficient energy utilization is driving research into ways to harvest ubiquitous waste heat. Here, we explore pyroelectric energy conversion (PEC) from low-grade thermal sources that exploits strong field- and temperature-induced polarization susceptibilities in the relaxor ferroelectric 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (PMN-PT). Relaxors have attracted considerable attention due to their intriguing dielectric and piezoelectric properties including high reversible strains and high-temperature operation, but there has been only minimal study of their electrothermal effects. Here, we develop a comprehensive picture of the relationship between epitaxial strain, structure, properties, and local polar order in relaxor thin films. We will discuss how high-quality, coherently-strained films of PMN-PT provide new understanding of structure and properties1 which opens doors for new applications. In particular, we explore how the electric-field-driven enhancement of the pyroelectric response (−550 μC m−2 K−1) and suppression of the dielectric response (by 72%) yield substantial figures of merit for PEC. Field- and temperature-dependent pyroelectric measurements highlight the role of polarization rotation and field-induced polarization in mediating these effects. Solid-state, thin-film devices that convert low-grade heat into electrical energy are demonstrated using pyroelectric Ericsson cycles, and optimized to yield maximum energy density, power density, and efficiency of 1.06 J cm−3, 526 W cm−3 and 19% of Carnot, respectively; the highest values reported to date and equivalent to a thermoelectric with an effective ZT ≈ 1.16 for a temperature change of 10 K.2 We will also explore the potential for electrocaloric effects and routes to enhance the energy conversion potential of materials. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F02.00006: Electrode material effect on the switching behavior of ferroelectric HfO2-based thin films Pratyush Buragohain, Adam Erickson, Claudia Richter, Pamenas Kariuki, Monica Materano, Tony Schenk, Haidong Lu, Uwe Schroeder, Alexei Gruverman Application of HfO2-based films to ferroelectric memory and logic devices has generated considerable interest as they allow overcoming significant problems associated with poor compatibility of perovskite ferroelectrics with CMOS processing. However, detailed studies of such application-relevant properties as imprint and polarization switching dynamics with respect to the electrode material and processing condition are still sparse in literature. Here, we use a combination of Piezoresponse Force Microscopy (PFM) and pulse switching techniques to analyze the time- and field-dependent evolution of the domain structure in Hf0.5Zr0.5O2 and La:HfO2 thin film capacitors with oxygen rich/deficient electrodes. Switching spectroscopy-PFM (SS-PFM) maps revealed the electrode-dependent spatial variations in the local potential landscape, which strongly affect the domain switching kinetics. It is shown that stronger oxidation reduces the internal imprint bias while also leading to an increase in the remanent polarization. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F02.00007: ABSTRACT WITHDRAWN
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Tuesday, March 5, 2019 1:27PM - 1:39PM |
F02.00008: Probing short-range polar order in PZN-xPT and PMN-xPT relaxor ferroelectrics with neutron scattering Zhijun Xu, Guangyong Xu, Peter M Gehring, Chris Stock, Fei Li, Shujun Zhang, Z. -G. Ye We have performed neutron scattering measurements on single crystal PZN-xPT and PMN-xPT samples. One of the key issues in these materials is the role of polar nano-regions (PNR), how the short-range orders coexist with long-range polar order and influence the bulk property. With diffuse scattering measurements carried out under external field along different directions, we were able to monitor how the dominant part of the diffuse scattering of "butterfly diffuse" that extends along <110> directions change with field. We observe an anormal suppression of diffuse scattering in Tetragonal phase near 400K and recover in Rhombohedral phase. We also investigate acoustic phonon, which are also affectted in the same narrow temperature range. Our results suggest that the polar nano-regions are robust local orders that are locked in within the surrounding polar environment below Tc, and also strongly interact with acoustic phonon modes that induces instability in these systems. |
Tuesday, March 5, 2019 1:39PM - 2:15PM |
F02.00009: New approaches to understanding the ferroic properties of perovskite oxide solid solutions Invited Speaker: Andrew Rappe The dielectric properties of ferroelectric materials are a key driver of smart materials applications. In this talk, two key aspects of anomalous dielectric enhancement will be analyzed: domain walls and relaxor ferroelectrics. A comprehensive theoretical viewpoint will be sketched that unifies these aspects, based on multi-scale materials modeling. |
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