Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F37a: Dielectric and Ferroelectric Oxides IIFocus
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Sponsoring Units: DMP DCOMP Chair: Adam Kaminsky, Ames Laboratory and University of Iowa Room: 383 |
Tuesday, March 14, 2017 11:15AM - 11:51AM |
F37a.00001: The various contributions to the diffuse scattering from PMN-xPT Invited Speaker: Daniel Phelan Relaxor ferroelectrics, which have large electromechanical coupling, possess temperature and electric field dependent local atomic displacements that lead to diffuse patterns in diffraction experiments. Here, we discuss several different contributions to the diffuse scattering in the lead-based relaxor ferroelectrics, PMN-xPT. Insight into these contributions has been gained through measurements that employ state-of-the-art neutron and x-ray instrumentation allowing for efficient measurements of three-dimensional diffuse scattering over large wave-vector ranges and thus many Brillouin zones. Such measurements have been performed on a number of crystals which reveal the compositional dependence of the different features as the system morphs from a 'relaxor' character into a 'ferroelectric' character upon increasing x. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:03PM |
F37a.00002: A phonon fluctuation state in the stuffed tridymite-type oxides Ba$_{1-x}$Sr$_x$Al$_2$O$_4$ Yui Ishii, Shogo Kawaguchi, Hirofumi Tsukasaki, Yuhya Ouchi, Shigeo Mori The paraelectric phase (space group $P6_322$) of the stuffed tridymite-type ferroelectric BaAl$_2$O$_4$ has recently been reported to possess the energetically competing low-energy phonon modes at the M- and K-points, both of which soften at $T_{\rm C}$ simultaneously [Y. Ishii et al., Phys. Rev. B 93, 134108 (2016).]. The M-point mode condenses at $T_{\rm C}$=450 K, giving rise to the low-temperature ferroelectric phase ( $P6_3$), whereas the K-point mode is electrostatically unfavorable and just disappears below $T_{\rm C}$. In this study, we investigated the thermal diffuse scatterings in the electron diffraction and the dielectric properties of Ba$_{1-x}$Sr$_x$Al$_2$O$_4$ ($x = 0-0.5$). We present that Ba$_{1-x}$Sr$_x$Al$_2$O$_4$ system exhibits a "fluctuating'' state, in which the M-point soft mode does not condense but survives and fluctuates down to low temperature, below $T^*\sim200$ K. Although the K-point soft mode disappears below $T^*$, the $P6_322$ crystal structure is retained at temperatures down to 15 K. The wave vector of the M-point diffuse scatterings is temperature dependent below $T^*$ and loses commensurateness as the temperature decreases. This result indicates that the fluctuation in the wave vector of the M-point mode increases at low temperatures. [Preview Abstract] |
Tuesday, March 14, 2017 12:03PM - 12:15PM |
F37a.00003: Room temperature electric-field control of magnetism in layered oxides with cation order Xuezeng Lu, James M. Rondinelli Searching for materials with room-temperature electric-field control of magnetism has interested researchers for many years with three-dimensional perovskite BiFeO3-based compounds as the main focus. Here we choose the layered hybrid improper ferroelectric Ruddlesden-Popper oxides as a platform from which to realize electric field controllable magnetism, leveraging a recently identified strain tunable polar-to-nonpolar (P-NP) transition. We first propose a design principle for selecting the required A and B cation chemistries that ensure strained A3B2O7 (001) --oriented films exhibit the P-NP transitions, which we substantiate with density functional calculations. We next extend our guideline to B-site ordered A3BB$\prime $O7 oxides to expand the number of available compounds exhibiting P-NP transitions. We then demonstrate electric-field controllable weak ferromagnetism at the boundary of the P-NP transition in magnetic (001) A3BB$\prime $O7 films and propose new compounds for route to room temperature magnetoelectric multiferroics. [Preview Abstract] |
Tuesday, March 14, 2017 12:15PM - 12:27PM |
F37a.00004: Structural evolution in the hybrid improper multiferroic Ca$_{\mathrm{3-x}}$Sr$_{\mathrm{x}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ F. Ye, J. A. Fernandez-Baca, Jieming Sheng, Bin Gao, Sang-Wook Cheong A novel microscopic mechanism has been proposed to search for ferroelectric material for realistic applications. The instability of the polar phonon mode is driven by the simultaneous condensation of two nonpolar lattice modes associated with oxygen octahedron rotation and tilt, and is responsible for the polar symmetry observed in the Ruddlesden-Popper compound. Unlike the well-studied Ca$_{\mathrm{3}}$Mn$_{\mathrm{2}}$O$_{\mathrm{7}}$ where a antiferromagnetic order sets in at 120 K and displays strong interplay between the magnetism and structural distortion, the nonmagnetic Ca$_{\mathrm{3-x}}$Sr$_{\mathrm{x}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ only exhibits a competition between two structural distortion modes. We used single crystal neutron diffraction to investigate the temperature and doping evolution of the crystal structure in a series of Sr-doped Ca$_{\mathrm{3}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ where the in-plane rotation of TiO$_{\mathrm{6}}$ is gradually suppressed and the out-of-plane tilt persists with increasing Sr concentration for x\textless 1.0. The corresponding structural temperature from the low-T orthorhombic to the high-T tetragonal phase also increases steadily with Sr doping. Our diffraction study provides detailed characterization of spontaneous polarization that can be achieved through tilt engineering of the TiO$_{\mathrm{6}}$ environment. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 12:39PM |
F37a.00005: First-principles-based Landau energy functionals for perovskite ferroelectrics Krishna Chaitanya Pitike, Neha Gadigi, John Mangeri, Valentino Cooper, Serge Nakhmanson ABO$_{3}$ perovskite-oxide ferroelectrics are well known for their useful functional properties. These materials, as well as their solid solutions, exhibit rich phase diagrams that can be exploited, e.g., to obtain large piezoelectric and dielectric responses. Mesoscale-level investigations of their behavior usually utilize Landau phenomenological theory, where the system energy functional is represented by a polynomial expansion in powers of polarization and strain that is parameterized from experimental data. In this project, we present an approach for fitting the Landau functionals for perovskite ferroelectrics directly from first principles simulations with the help of statistical and machine learning tools. Initial data sets are created by computing the energies for a wide range of possible structural configurations involving polar and elastic distortions with standard density-functional theory (DFT) codes. A small fraction of this data is then processed by supervised machine learning algorithms to train a Landau-style polynomial model that can predict the system energies to within 20 meV of the DFT results. [Preview Abstract] |
Tuesday, March 14, 2017 12:39PM - 12:51PM |
F37a.00006: Nonlinear optical detection of mixed phases in Ba(Zr,Ti)O$_{\mathrm{3}}$ films Yuhang Ren, David Ascienzo, Jun Ouyang High energy density, nonlinear dielectrics have attracted intensive research interest because of their outstanding energy storage performances. We report on the detection of phase separated microstructures in Ba(Zr,Ti)O$_{\mathrm{3}}$ (BZT) films by using optical SHG spectroscopy in the reflection and transmission geometries. The SHG responses clearly show mixed tetragonal (T) and rhombohedral (R) domains at various thicknesses, T-phase and R-phase dominated respectively. The fraction of the R phase increases with film thickness, while the T phase decreased as reflected by the variations of SHG intensities. We reveal that the initial mismatch between BZT film and substrate is extremely important to manage the strain field across the BZT film and therefore phases. The conversion of one phase into another under an external electric field causes extra delay in polarization saturation, contributing to a larger breakdown field on top of the scaling effect. [Preview Abstract] |
Tuesday, March 14, 2017 12:51PM - 1:03PM |
F37a.00007: The radom electric field problem of relaxor ferroelectrics Gian G. Guzman-Verri, Jose Rafael Arce-Gamboa, Charlie Hultgreen-Mena Relaxor ferroelectrics are remarkable complex oxide materials: they exhibit diffuse phase transitions with a large frequency dependent dielectric constant over a broad temperature range, non-ergodic behaviour, and huge piezoelectric responses. Their characteristic long-ranged and anisotropic dipolar forces, cubic environment and random electric field make relaxors unique ferroic systems for studying the effects of compositional disorder in phase transitions. While significant progress has been made in recent years towards a more complete understanding of the relaxor behaviour, its mechanism has not been fully understood. It has been pointed out that one of the main challenges is that the problem of random electric fields in cubic systems has not been understood. In this talk, we discuss this problem within a minimal microscopic model and contrast the predicted static dielectric properties with those observed for typical relaxors such as PMN-PT. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:15PM |
F37a.00008: Diffuse Scattering from PbZr$_{1-x}$Ti$_{x}$O$_{3}$ Matthew Krogstad, Stephan Rosenkranz, Raymond Osborn, Omar Chmaissem, Feng Ye, Jacob Ruff, Peter Gehring, Zuo-Guang Ye, Daniel Phelan Alloying the ferroelectric PbTiO$_{3}$ with the anti-ferroelectric PbZrO$_{3}$ produces PbZr$_{1-\textit{x}}$Ti$_{\textit{x}}O_{3}$, a system featuring a morphotropic phase boundary around \textit{x}=0.48. Near this phase boundary, the piezoelectric properties of the system are greatly enhanced. It is thought that this behavior may be related to the addition of some short-range order phenomena arising from competition between the differing long-range orders of the parent systems. To investigate possible short-range ordering, diffuse scattering measurements were performed on a single crystal of PbZr$_{0.54}$Ti$_{0.46}$O$_{3}$ producing large volumes of reciprocal space intensities from both neutron and x-ray diffraction. Our experiments evidence significant short-range correlations that provide an interesting contrast to related relaxor and ferroelectric systems. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F37a.00009: Lattice rotation vortex observed between polar nanoregions in relaxor-ferroelectric (1-x)Pb(Zn$_{\mathrm{1/3}}$Nb$_{\mathrm{2/3}})$O$_{\mathrm{3}}$-xPbTiO$_{\mathrm{3}}$ single crystal Yu-Tsun Shao, Jian-Min Zuo Domain walls (DWs) play a critical role in determining the polarization switching behavior in relaxor-based ferroelectric crystals. The domains in relaxor-ferroelectric crystals consist of polar nanoregions (PNRs) and their interface is poorly understood. Here, we report an energy-filtered (EF-) scanning convergent beam electron diffraction (SCBED) study for the identification of PNRs and determination of their interface. With the aid of electro dynamical diffraction simulation, nanometer-sized PNRs having monoclinic \textit{Pm} (M$_{\mathrm{C}})$ symmetry in single crystal PZN- 8{\%}PT were identified. Lattice rotation vortices having an average radius of \textasciitilde 7 nm at the 50$^{\circ}$ DWs were revealed by maps of crystal orientations, domain configurations, symmetry breaking. Such measurements suggest the merging of 2D and 1D topological defects, with implications for domain-switching mechanisms in relaxor ferroelectric crystals. The interplay between polarization, charge, and strain degrees of freedom suggests a complex landscape of topological defects in ferroelectrics that may be explored for a new form of nanoscale ferroelectric devices. [Preview Abstract] |
Tuesday, March 14, 2017 1:27PM - 1:39PM |
F37a.00010: Antiferroelectric nanodomains in morphotropic solid solutions. Vladimir Sobolev, Valeriy Ishchuk, Danil Kuzenko It is demonstrated that the decomposition of solid solutions in the vicinity of the boundaries separating the tetragonal and rhombohedral phases in compounds with compositions from the morphotropic boundary region of the ``temperature-composition'' phase diagram leads to the formation of segregates and to the changes of the solid solution's chemical composition. The appearance of the antiferroelectric nanodomains is possible as a result of the local decomposition of the solid solution and Zr enrichment of local regions in the vicinity of interphase boundaries. It is also shown that the proper thermoelectric treatment of samples containing these segregates can give substantially higher values of piezoelectric parameters in the PZT-based compounds. [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F37a.00011: Scalable ferroelectric MOS capacitors comprised of single crystalline SrZrxTi1-xO3 on Ge. Reza Moghadam, Z.-Y. Xiao, K. Ahmadi-Majlan, E. Grimley, P.V. Ong, J. M. Lebeau, S. A. Chambers, X. Hong, P. Sushko, J. H. Ngai The epitaxial growth of multifunctional oxides on semiconductors has opened a pathway to introduce new functionalities to semiconductor device technologies. In particular, ferroelectric materials integrated on semiconductors could lead to field-effect devices that require very little power to operate, or that possess both logic and memory functionalities. The development of metal-oxide-semiconductor (MOS) capacitors in which the polarization of a ferroelectric gate is coupled to the surface potential of a semiconducting channel is essential in order to realize such field-effect devices. Here we demonstrate that scalable, ferroelectric MOS capacitors can be realized using single crystalline SrZrxTi1-xO3 (x$=$ 0.7) that has been epitaxially grown on Ge. Single crystalline SrZrxTi1-xO3 exhibits characteristics that are ideal for a ferroelectric gate material, namely, a type-I band offset with respect to Ge, large coercive fields and polarization that can be enhanced with electric field. The latter characteristic stems from the relaxor nature of SrZrxTi1-xO3. These properties enable MOS capacitors with 5 nm thick SrZrxTi1-xO3 layers to exhibit a nearly 2 V wide hysteretic window in the capacitance-voltage characteristics. The realization of ferroelectric MOS capacitors with technologically relevant gate thicknesses opens the pathway to practical field effect devices. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F37a.00012: Modulation of ferroelectricity and resistance switching in SrTiO$_{\mathrm{3}}$ films Fang Yang, Weihua Wang, Jiandong Guo SrTiO$_{\mathrm{3}}$ has remarkable dielectric property; it also exhibits ferroelectricity in thin films with strain or defects. It is expected that modulation of its ferroelectricity and electricity is potential in oxide electronics. The nonstoichiometry SrTiO$_{\mathrm{3}}$ thin films with different cation concentrations were prepared on Si (001) substrates. Piezoresponse force microscopy measurements show that those films with Sr deficiency display obvious ferroelectricity. The scanning transmission electron microscopy results show that there are interstitial Ti atoms in the unit cells. Polar defect pairs can be formed by the interstitial Ti atoms and Sr vacancies along [100] or [110] direction. Such antisitelike defects observed in SrTiO$_{\mathrm{3}}$ films are considered as the origin of the ferroelectricity. In this way, the SrTiO$_{\mathrm{3}}$ ferroelectricity can be modulated by control the concentration of the antisitelike defects via changing the cation concentration. Further, [(SrTiO$_{\mathrm{3}})_{\mathrm{3}}$/(LaTiO$_{\mathrm{3}})_{\mathrm{2}}$]$_{\mathrm{3}}$ superlattices have been prepared on 0.67[Pb(Mg$_{\mathrm{1/3}}$Nb$_{\mathrm{2/3}})$O$_{\mathrm{3}}$]-0.33[PbTiO$_{\mathrm{3}}$] (PMN-PT) substrate. The superlattices show resistance switching under the ferroelectric polarization of the PMN-PT substrate. The on/off ratio of the interfacial resistance is about 20{\%}\textasciitilde 25{\%}. This can be applied in oxide electronics in potential. [Preview Abstract] |
Tuesday, March 14, 2017 2:03PM - 2:15PM |
F37a.00013: Piezoelectric and Dielectric Properties of PbZr$_{\mathrm{0.2}}$Ti$_{\mathrm{0.8}}$O$_{\mathrm{3}}$/ZnO heterostructures. Juan Wang, Pavel Savel, Alexei Grigoriev The dielectric and piezoelectric properties of epitaxial ZnO films and PbZr$_{\mathrm{0.2}}$Ti$_{\mathrm{0.8}}$O$_{\mathrm{3}}$/ZnO heterostructures were studied by electrical measurement and time-resolved x-ray diffraction (TRXRD). ZnO epitaxial thin films were prepared on n-GaN/Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ (0001)-oriented substrates by rf magnetron sputtering. A typical diode I-V behavior of pure ZnO films evolved into a ferroelectric switching hysteresis loop after the deposition of a thin PbZr$_{\mathrm{0.2}}$Ti$_{\mathrm{0.8}}$O$_{\mathrm{3}}$ (PZT) layer on top of the epitaxial ZnO film. A hysteresis was also observed in C-V characteristics of the heterostructure. TRXRD revealed piezoelectric strain in ZnO and PZT layers under an applied electric field. The simultaneous measurements of internal strains and I-V characteristics of the ferroelectric/semiconductor heterostructure enable direct access to internal electric fields, charge and polarization dynamics. This information provides unique opportunities to understand and control electronic properties of semiconductors by polarization coupling with ferroelectric materials. [Preview Abstract] |
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