Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session D02: Ferroelectrics and Relaxors |
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Sponsoring Units: DMP Chair: Mahmoud Asmar, Kennesaw State University Room: L100B |
Monday, March 4, 2024 3:00PM - 3:12PM |
D02.00001: Investigating Ferroelectricity in bulk Tellurium doped Tin Sulfide (SnSTe) Bamidele O Onipede, Hui Cai, Matthew E Metcalf Under strain gradients, polarization could spontaneously develop locally around the source of the strain. Since other piezoelectric coefficients contribute to out-of-plane deflections, the departure from perfect flatness of bulk crystals could lead to the presence of non-zero out-of-plane polarization. The insertion of larger atomic radius tellurium into ferroelectric bulk tin sulfide (SnS) is expected to add local strain gradients within the host crystal in addition to breaking the centrosymmetry of the bulk SnS. By using bottom-up synthesis method of chemical vapour deposition (CVD), we successfully synthesize in this work bulk tellurium doped SnS. Analysis has been done via optical microscopy, atomic force microscopy, piezoresponse force microscopy, Raman spectroscopy and X-Ray photoelectron spectroscopy with a confirmation of successful synthesis of the Te doped alloy. Ideal synthesis parameters in our CVD setup has been identified via systematic limit testing of the parameters. We show in this work the result of our work towards the observation of piezoelectric coupling in the bulk phase of materials which is critical in technological applications where minimal thickness is not necessary. |
Monday, March 4, 2024 3:12PM - 3:24PM |
D02.00002: Phonon decoupling in oxides Yeongrok Jin, Jaekwang Lee Brownmillerite has emerged as a promising candidate for innovative ferroelectric applications, and it can be obtained by topotactically reducing the perovskite structure. Due to the distinct alignment of oxygen vacancy channels, unusual properties manifest, including ferroelectricity. Theoretically, BO4 tetrahedral distortion could induce inversion symmetry breaking within the crystal structure, and both ionic displacement and rotation of the FeO4 tetrahedra can be combined in brownmillerite SrFeO2.5 (SFO) and CaFeO2.5 (CFO), revealing a unique one-dimensional collective distortion. In these intriguing brownmillerite structures, phonons exhibit unique behaviors that have not yet been fully explored. This study investigates the decoupling of phonon modes associated with oxygen-octahedra from those with oxygen-tetrahedra in brownmillerite oxides. We find that such localized oxygen-tetrahedral phonons enable site-selective control of the unit cell-wide domain. By combining simple 2D modelling and density functional theory (DFT) calculations, we have uncovered the underlying mechanism responsible for phonon decoupling. Our findings demonstrate that specific structural characteristics within the brownmillerite framework lead to the independent vibration of oxygen-octahedra and oxygen-tetrahedra. In this presentation, we will detail our results regarding 2D modeling, phonon band structure, and the implications for ferroelectricity in brownmillerite oxides. |
Monday, March 4, 2024 3:24PM - 3:36PM |
D02.00003: Tuning ferroelectricity in BaTiO3 freestanding membranes via novel strain states: Insights from first-principles calculations Md Kamal Hossain, Elizabeth A Nowadnick Advancements in materials synthesis techniques have enabled the fabrication of perovskite oxide materials in the form of freestanding membranes. Recent research has shown that these ferroelectric oxide membranes exhibit faster switching times and reduced switching energies compared to their substrate-constrained thin-film counterparts. However, the underlying mechanisms and strategies for optimizing these properties remain largely unexplored. In addition, freestanding membranes present new opportunities for the design and utilization of novel strain states, whereby strains of distinct amplitudes may be applied along different crystallographic axes. In this work, we employ density functional theory calculations to investigate the properties of prototypical ferroelectric perovskite BaTiO3 under applied strain states of various symmetries, considering strains along one (uniaxial) or two (biaxial) axes of varying relative amplitudes. We find that these distinct applied strain states lead to diverse strain-induced polar phase sequences in BaTiO3 and track the computed spontaneous polarizations as a function of strain. Additionally, we explore how to design strain states to facilitate lower ferroelectric switching barriers. These results advance our understanding of strain-mediated tuning of ferroelectric oxide membranes, which may find application in next-generation low-power electronic devices. |
Monday, March 4, 2024 3:36PM - 3:48PM |
D02.00004: Deep Potential Molecular Dynamics Study of PMN Relaxor Ferroelectricity Kehan Cai, Pinchen Xie, Roberto Car We investigate the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) crystal through all-atom molecular dynamics simulations, employing a neural-network potential energy model (Deep Potential) trained on density functional theory (DFT) data with the SCAN approximation. With consistent DFT data on maximally localized Wannier functions, another neural network model (Deep Wannier) is trained to predict the bulk polarization of PMN. The static and frequency-dependent susceptibility of PMN predicted by our models are found to qualitatively agree with experiments. |
Monday, March 4, 2024 3:48PM - 4:00PM |
D02.00005: Electrocaloric Performance of High-Entropy Oxides from First Principles Tara Karimzadeh Sabet, Ismaila Dabo The electrocaloric effect holds significant promise for advancing sustainable solid-state refrigeration technologies. High-entropy oxides [1] are potentially advantageous due to the thermal stability of their polar phases. In this work, we evaluate the phase stability and electrocaloric performance of the high-entropy perovskite (Na,Bi,Sr,Ba,Ca)TiO3. A pivotal parameter in evaluating electrocaloric performance is the dependence of adiabatic electrocaloric temperature change as a function of temperature, which is intricately linked to the change of polarization with respect to temperature under a constant electric field [2]. To predict this parameter, we developed models for the temperature-dependent polarization P(T) of high-entropy oxides taking into account chemical disorder and local distortions. We systematically assess the efficiency and accuracy of the proposed models for mapping the temperature-dependent free energy landscape across high-entropy oxide compositions. |
Monday, March 4, 2024 4:00PM - 4:12PM |
D02.00006: Electric field dependent thermal conductivity on relaxor ferroelectric PMN-PT Delaram Rashadfar, Brandi L Wooten, Joseph P Heremans Polarization caloritronics is an emerging field dedicated to investigating thermal fluctuations within the polarization of ferroelectrics, which Bauer et al. [1] labels "ferrons." Wooten et al. [2] measure the electric field dependencies of the thermal conductivity (k), diffusivity (D) and longitudinal acoustic sound velocity (v_LA) of ferroelectric Pb(Zr,Ti)O3 (PZT), identify ferrons in this material to include acoustic phonons and explain the results quantitatively and without adjustable parameters in terms of the piezoelectric coefficients (d33 and d31), which strain-mixes optical and acoustic modes, and the Grüneisen parameter (γ). Here, we measure k, v_LA and d31 of a ferroelectric relaxor, Pb[Mg1/3Nb2/3]O3 - PbTiO3 (PMN-PT) and confirm the validity of the theory, again without adjustable parameters. The effects of field E on PMN-PT are of opposite polarity and an order of magnitude larger than on PZT. Furthermore, k-measurements revealed a significant alteration in behavior as the electric field was cycled more than ten times through the field-induced crystallographic phase transitions of PMN-PT: the effects changed sign again. An experimental investigation of d31 values for both a pristine and a cycled sample shows that it is this parameter that changes, and that the theory holds. |
Monday, March 4, 2024 4:12PM - 4:24PM |
D02.00007: Dynamics of the electrocaloric effect: high-resolution measurements on microsecond timescales Jan A Fischer, Joerg Rudolph, Daniel Haegele The electrocaloric effect (ECE) in ferroelectrics is a promising candidate for improved cooling technologies and small cooling devices. While direct and reliable measurements of the reversible adiabatic temperature change ΔT as a caloric key parameter are already challenging, an access to the full dynamics ΔT(t) of the ECE and the correlation with the ferroelectric properties are highly desirable for a more fundamental understanding of the ECE. |
Monday, March 4, 2024 4:24PM - 4:36PM |
D02.00008: Understanding Switching in Hexagonal Ferroelectrics by Combining Large-scale Reactive MD and Experiments Abhijeet S Dhakane, Alireza Sepehrinezhad, Kyle P Kelly, Adri C.T. van Duin, Ganesh Panchapakesan The recent discovery of multi-functional properties such as ferroelectricity in the hexagonal nitride and oxide materials has generated renewed interest in them, due to their compatibility with existing CMOS integration. These materials have high durability, large band gaps and possess tunable optical and piezoelectric properties by doping. Yet, the origin of ferroelectricity, and its switching mechanism under electric-fields remain unclear, making it difficult to design improved hexagonal ferroelectrics that can switch at lower coercive fields to enable low-power microelectronic devices. We have performed large-scale simulations (> 60K atoms) of field-induced switching of wurtzite-ZnO using reactive force-fields and analyzed the trajectory along the hysteresis loop using novel data analytics to unravel the switching mechanism. In this talk, we will present the atomistic switching mechanism, extract relevant energy-barriers for switching and additional insights from our analysis, and compare with available experiments to validate our findings. |
Monday, March 4, 2024 4:36PM - 4:48PM |
D02.00009: Abstract Withdrawn
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Monday, March 4, 2024 4:48PM - 5:00PM |
D02.00010: Strain fluctuations unlock ferroelectricity in wurtzites Steven M Baksa, Simon Gelin, Seda Oturak, Susan E Trolier-Mckinstry, Jon-Paul Maria, Andrew M Rappe, Ismaila Dabo Ferroelectrics are of interest for non-volatile data storage due to their reorientable, crystallographically defined polarization states, yet efforts to integrate perovskites into ultrathin memories have been frustrated by film-thickness scaling constraints, limiting ferroelectric switching under low voltage. Wurtzites [1], including magnesium-substituted zinc oxide [(Zn,Mg)O] [2], have recently been shown to exhibit scalable ferroelectricity. While first-principles calculations suggest that a biaxial tension of a few percent promotes ferroelectricity in wurtzites [3,4], biaxial strains are found to not exceed 0.3% in (Zn,Mg)O at the solubility limit of Mg in bulk ZnO. In this work, we explain the observations of ferroelectricity in (Zn,Mg)O by examining the influence of Mg substitution on interatomic bonding and ferroelectric switching. We demonstrate that large strain fluctuations emerge locally around Zn and Mg cations in (Zn,Mg)O, causing a reduction of up to 45% in the local coercive fields via sequential polarization reversal. This work opens up an avenue to develop scalable ferroelectrics for ultrathin microelectronics. |
Monday, March 4, 2024 5:00PM - 5:12PM |
D02.00011: Hafnia is a proper ferroelectric Aldo Raeliarijaona, Ronald E Cohen The nature of ferroelectricity in hafnia is still unclear as some studies consider hafnia as an improper ferroelectric[1][2], whereas some experimental evidence and density functional theory calculations suggest otherwise[3][4]. We clarify and demonstrate that ferroelectricity in hafnia is indeed proper. Using symmetry analysis, DFT for structural optimization, and density functional perturbation theory we investigate the dynamical stability of the structures derived from fluorite cubic. We examine the group-subgroup relations between relevant hafnia phases and demonstrate that, upon adequately choosing the parent structure, all polar hafnia phases — Pca21, Pmn21, R3m and R3— result from the distortion of single, unstable polar mode of the parent structure as they all exhibit double-well potential that are relatively shallow. [1] H.-J. Lee et al., Science 369, 1343 (2020)
[2] F. Delodovici, P. Barone, and S. Picozzi, Phys. Rev. Mater. 5, 064405 (2021).
[3] H. Arramberri and J. Íñiguez, arXiv:2302.00688.
[4] U.Schroeder et al., Advanced Electronic Materials 8, 2200265 (2022).
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Monday, March 4, 2024 5:12PM - 5:24PM |
D02.00012: Phase modulation of Hf0.5Zr0.5O2/La0.7Sr0.3MnO3 heterostructure by growth orientation mediated strain engineering ARNAB DE, SEUNG GYO JEONG, Jin Young Oh, Seong Bin Bae, Hojin Lee, Taekjib Choi, Sang Mo Yang, Young hoon Kim, Young Min Kim, Woo Seok Choi Robust ferroelectric properties in HfO2 based ultrathin films have the potential to revolutionize nonvolatile memories applications in nanoscale devices. However, to fully exploit the potential of ferroelectric HfO2-based thin films, we must address fundamental questions regarding the origin of ferroelectricity and develop strategies for controlled implementation. The stability of the polar orthorhombic phase responsible for the robust polarization is believed to be influenced by various extrinsic factors, including finite-size effects, surface/interface effects of small grains, compressive stress, dopants, and oxygen vacancies. In this study, we investigate the influence of substrate orientations on the relative stability of different phases of Hf0.5Zr0.5O2 (HZO) grown epitaxially on (001) and (110) oriented La0.7Sr0.3MnO3 /SrTiO3 using pulsed laser epitaxy (PLE). We demonstrate that stable polarization can be achieved in (111) oriented HZO in both types of the substrates however (110) oriented substrates promote a high degree of structural order (crystallinity) and better stability of the orthorhombic phase of HZO. Ferroelectric measurement reveals remanent polarization as high as 28 µC/cm2 without any wake-up effect. This study suggests that tuning of the epitaxial growth of ferroelectric HZO with suitable strain conditions allows the improvement of stability of the metastable ferroelectric phase that could be used for better optimization of the device applications. |
Monday, March 4, 2024 5:24PM - 5:36PM |
D02.00013: Understanding and Controlling the Energy Landscape of Hf0.5Zr0.5O2 Jack Broad, Pratik Brahma, Sinéad M Griffin, Zhi (Jackie) Yao, Prabhat Kumar, Jorge A Munoz, Sayeef Salahuddin As the thickness of field effect transistors (FETs) reaches the atomic limit, attention has shifted towards increasing the functionality of FETs to preserve Moore’s law. Enhanced FET functionality can be achieved by modifying the gate oxide, and Hf0.5Zr0.5O2 (HZO) has proven to be incredibly effective to this end. |
Monday, March 4, 2024 5:36PM - 5:48PM |
D02.00014: Effect of Strain on ferroelectric Y-doped HfO2 Adedamola D Aladese, Xiao Shen Ferroelectric hafnium dioxide (HfO2), also known as hafnia, is promising for applications in field effect transistors and nonvolatile memories due to its compatibility with current complementary metal-oxide-semiconductor (CMOS) technology. However, a major challenge of the HfO2-based ferroelectrics is the stabilization of the ferroelectric phases versus other competing phases. Experimental studies have confirmed that the Y-doping of HfO2 is a viable option for addressing this challenge. While these experimental results are not fully understood, there are emerging findings that biaxial strains, especially along the (111) direction, may also play an important role in the in-phase formation of the ferroelectric phase. Here, we report an investigation of the effects of biaxial strain on the phase stabilization of Y-doped HfO2 using first-principles density functional theory (DFT) calculations. The separate and combined effects of strain and Y-doping are discussed. In addition, we identify the impacts of oxygen vacancies arising from doping in phase stabilization. |
Monday, March 4, 2024 5:48PM - 6:00PM |
D02.00015: Lowering of effective oxide thickness due to negative capacitance effects in polycrystalline ferroelectric HZO gate stacks Prabhat Kumar, Michael Hoffmann, Andrew J Nonaka, Sayeef Salahuddin, Zhi (Jackie) Yao Hafnium Zirconium Oxide (HZO) superlattice heterostructures have emerged as a promising candidate for the gate stack of a ferroelectric field-effect-transistor. Recent work has experimentally demonstrated that a tetragonal/orthorhombic (t/o-) phase mixture with partially in-plane polarization can lead to energy landscape flattening and negative capacitance (NC) stabilization. However, there is a need for understanding the physical mechanisms of formation of domains and their dynamics to characterize the origin of NC effects in such gate stacks. In this work, we will present a 3D phase-field study to quantify the lowering of effective oxide thickness (EOT) in metal-ferroelectric-insulator-semiconductor heterostructures with realistic grain sizes. Our results show that the achievable EOT critically depends on the angle of the polar axis, the grain-size, t-phase fraction, and the density of domains. |
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