Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V04: Dielectric & Ferroic Oxides -- Structure, Phase Stability, and Competition IIFocus
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Sponsoring Units: DMP DCOMP Chair: Cyrus Dreyer, Stony Brook University Room: BCEC 107C |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V04.00001: Nature of the Phase Transitions Leading to Hybrid Improper Ferroelectricity in Ca3X2O7 Sizhan Liu, Han Zhang, Sanjit Ghose, Mali Balasubramanian, Zhenxian Liu, SuYin Grass Wang, Yu-Sheng Chen, Bin Gao, Jaewook Kim, Sang-Wook Cheong, Elizabeth Nowadnick, Trevor Tyson Detailed structural and optical measurements reveal that the tilt and rotation distortion relative to the high symmetry phase driving ferroelectricity in the system Ca3X2O7 system (X=Mn and Ti) condense at different temperatures. The condensation of the rotation and tilt distortions at distinctly different temperatures is unexpected. Experimental results, combined with DFT simulation of the atomic force constants, suggest that this loss of a polar state is driven by the relative strength of the A-O bonds to the X-O bonds. Raman measurements under isotropic pressure are used to assess the stability of the tilt and rotational distortions. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V04.00002: Lattice dynamics of hybrid improper ferroelectric (Ca,Sr)3Ti2O7 Dipanshu Bansal, Jennifer L Niedziela, Xing He, Tyson Lanigan-Atkins, Ayman Said, Ahmet Alatas, Douglas L Abernathy, Yang Ren, Bin Gao, Sang-Wook Cheong, Olivier Delaire In hybrid improper ferroelectric (Ca,Sr)3Ti2O7, the anharmonic coupling between a stable zone-center polar phonon mode and two unstable zone-boundary non-polar modes, and quasi-2D behavior of c-polarized acoustic modes are theoretically proposed but remain to be experimentally validated. We have performed comprehensive T-dependent single-crystal diffraction, calorimetry, and phonon measurements in (Ca,Sr)3Ti2O7 for x = 0, 0.6, and 0.9, including the behavior across the ferroelectric transition Tc. We also performed first-principles phonon simulations. Our results revealed a strong broadening but little shifting of mean phonon energy on heating across Tc. Among two unstable modes, rotational mode remains robust, but the tilt mode shows substantial softening on heating, consistent with previous studies. However, contrary to previous simulations, our momentum and energy resolved inelastic x-ray scattering measurements did not show a quadratic dispersion of acoustic modes, theoretically associated with a quasi-2D character. Our detailed lattice dynamics study enables to benchmark simulations of anharmonic phonons and associated thermodynamic properties such as thermal expansion and thermal conductivity. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V04.00003: Effect of cation ordering and pressure on n=2 Ruddlesden-Popper oxides from first principles Sriram Poyyapakkam Ramkumar, Elizabeth Nowadnick Octahedral tilts and rotations are ubiquitous in perovskite oxides and couple strongly to the electronic and magnetic properties. Furthermore, the interplay of octahedral rotations and layering can enable novel functionalities. For example, it has recently been shown that in n=2 Ruddlesden-Popper A3B2O7 layered perovskites, two octahedral rotations of different symmetries can induce a polarization via a trilinear coupling mechanism, known as hybrid improper ferroelectricity. While there has been extensive work on engineering octahedral rotation amplitudes and patterns in ABO3 perovskites, this has been much less studied in the Ruddlesden-Popper phases. By performing first-principles density functional theory calculations for a range of A3B2O7 materials, we explore two different approaches for engineering octahedral rotations in these systems. First, we consider the impact of A-site cation ordering (e.g. A2A’B2O7) on the energetics of a range of structural phases. Second, we elucidate the effect of hydrostatic pressure on octahedral rotation amplitudes and in turn on the energetics of the phases. We hence provide possible mechanisms to control the stability between polar and non-polar phases as well as tune structural distortions necessary for hybrid improper ferroelectricity. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V04.00004: First principles study of structure and electronic properties of a stannate Hybrid Improper Ferroelectric Shutong Li, Turan Birol Hybrid improper ferroelectricity provides a means to design lead-free ferroelectrics. Sr3Sn2O7, which is recently shown to be ferroelectric, can bring together the low electronic effective mass observed in stannates with the robust, switchable polarization of hybrid improper ferroelectricity. In this talk, we are going to present a systematically investigation on structure and electronic properties of Sr3Sn2O7 under biaxial strain. We find that the biaxial strain has significant effect on ground state structure, polarization switching, as well as the electronic structure. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V04.00005: Ultra-Small SrTiO3 Nanoparticles: Understanding the Polar Phases and Possible Ferrroelectricity Sizhan Liu, Nathaniel Hurley, Vitali Prakapenka, Eran Greenberg, Zhenxian Liu, Milinda Abeykoon, Stanislaus S Wong, Trevor Tyson Previous work revealed that 10 nm SrTiO3 (STO) nanoparticles host a polar and possibly ferroelectric phase stable under high pressure and over a broad range of temperatures. In this work, a full range of free standing nanoparticle samples between 2 and 60 nm have been studied and compared to bulk STO. Detailed structural and optical measurements are used to explore the evolution of the structure and corresponding phonon modes for varying temperatures and pressures. To understand the nature of the polar state and the existence of ferroelecricity, nonlinear optical measurements were conducted. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V04.00006: Pressure Induced Unusual Multiferroicity in Perovskite PbCoO3 Feng Lou We develop a global structure search approach to predict the ground state of magnetic materials based on the genetic algorithm. With this new approach, we predict that the unusual phase transitions can happen in the recently synthesized perovskite oxide PbCoO3 [J. Am. Chem. Soc. 139, 4574 (2017)] under the different hydrostatic pressure. At low pressure, the PbCoO3 phases are polar and weakly ferromagnetic, indicating that these phases are multiferroic. When the pressure is increased to 13 GPa, a polar-to-nonpolar transition takes place, which is associated with the charge order transition. The simultaneous A-site and B-site charge ordering pattern in the nonpolar phase is in agreement with the experimental result. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V04.00007: In-situ lego-like construction of Ruddelsden-Popper surfaces using octahedra building blocks. Prahald Siwakoti, Mohammad Saghayezhian, Zhen Wang, Yimei Zhu, Rosalba Fittipaldi, Antonio Vecchione, Jiandi Zhang The surface of Ruddelsden-Popper (RP) ruthenates provides a rich playground to study the emergent phenomena originating from the coupling of lattice, charge and spin, mediated through RuO6 octahedron network. Because of the octahedra rotation, Sr2RuO4 surface shows a (√2 ×√2)R45° reconstruction. In addition to enhanced bulk-like octahedral rotation, Sr3Ru2O7 surface displays octahedral tilt as well. In this work, using ultra-high-vacuum cleaved surface of Sr2RuO4 as a platform, we have sequentially grown different number of SrRuO3 unit cells (u.c.) thin films, to mimic progression of “surface layer/s” of Sr2RuO4 to those of higher RP ruthenates (i.e. one u.c. is equivalent to Sr3Ru2O7, two u.c. for Sr4Ru3O10 surface and so on). Combining low energy electron diffraction with transmission electron microscopy, we systematically study the evolution of the lattice structure and discuss their properties. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V04.00008: Computational discovery of Bi-based perovskite oxide polymorphs Oswaldo Dieguez, Akansha Singh, Viveka Nand Singh, Enric Canadell, Jorge Iniguez In this paper we present our recent study[1] of the energy surface of BiScO3, BiCrO3, BiMnO3, BiFeO3, and BiCoO3. In normal conditions, the bulk crystals of these materials show three very different variations of the perovskite structure: an antipolar phase, a rhombohedral phase with a large polarization along the space diagonal of the pseudocubic unit cell, and a supertetragonal phase with even larger polarization. With the aim of understanding the causes for this variety, we have used a genetic algorithm to search for minima in the energy surface of these materials. Our results show that the number of these minima is very large when compared to that of typical ferroelectric perovskites like BaTiO3 and PbTiO3, and that a fine energy balance between them results in the large structural differences seen. As byproducts of our search we have identified charge-ordering structures with low energy in BiMnO3, and several phases with energies that are similar to that of the ground state of BiCrO3. We have also found that a inverse supertetragonal phase exists in bulk, likely to be favored in films epitaxially grown at large values of tensile misfit strain. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V04.00009: Persistence of Acentricity in Doped Ferroelectrics through Changes in Chemical Bonding Daniel Hickox-Young, Danilo Puggioni, James M Rondinelli Although broken inversion symmetry is traditionally thought to be stabilized primarily by long-range interactions, numerous noncentrosymmetric semiconductors (NCSs) have been shown to retain their broken inversion symmetry at dopant concentrations more than sufficient to screen long-range interactions [1]. Despite the identification of short-range interactions as a key component in stabilizing acentricity, the precise mechanism behind this phenomenon remains unclear. We use density functional theory to investigate the effect of doping on the prototypical ferroelectric BaTiO3, focusing on changes in local chemical bonding as a potential explanation for the short-range interactions stabilizing the distortion. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V04.00010: Correlation between Rietveld refinement yielded spontaneous polarization and experimentally obtained polarization data for Bi2Mo1-xWxO6 nanomaterials Anurag Pritam, Vaibhav Srivastava Single phase perovskite Bismuth Molybadate, Bi2Mo1-xWxO6 [x=0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.10] compositions were prepared using microwave sintering in air for 5hours. The prepared compacted ceramics were characterized by X-ray diffraction (XRD) at room temperature and obtained XRD data was fitted for Rietveld refinement. The analysis of results confirmed the formation of the orthorhombic crystal structure with the space group of pca21. The atomic displacements for various sites a, b, c yielded close spontaneous polarization and indicated about schematic tilting of octahedrons atmospheric carbon adsorption as contamination on nano open surfaces. Reduced direction cosines indicated about increased strength of MoO6 octahedrons against IR absorptions as shown by FTIR analysis, due to large oxygen bond strength of tungsten W than molybdenum Mo in BMO materials. Contaminated carbon groups were confirmed via additionally appearing FTIR peaks |
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