Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A39: Focus Session: Phase Transitions and Domains in Ferroelectric Nanostructures I |
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Sponsoring Units: FIAP Chair: Sergei Kalinin, Oak Ridge National Laboratory Room: Colorado Convention Center 502 |
Monday, March 5, 2007 8:00AM - 8:36AM |
A39.00001: Hybrid semiconductor-ferroelectric and metal-ferroelectric nanostructures Invited Speaker: The reduction of scale and dimensionality of ferroelectric materials enables study and application of important size-dependent differences in the mechanism for ferroelectric stability. These scale and dimensionality reductions also facilitate new opportunities for integrating ferroics with other material systems for multi-functional nano-scaled devices. First, we review our recent progress in understanding ferroelectric stability and the finite size-dependent evolution of the ferroelectric phase transition temperature in single-component nanostructures and its implications. We present results of a versatile synthetic approach we have developed to produce multi-component nanostructures, with examples of semiconductor-ferroelectric and metal-ferroelectric hybrid nanostructures. We discuss characterizations of their component structure and composition, and we also present the results of measurements of the properties of these hybrid nanostructures as individually and electrically addressable device elements. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 8:48AM |
A39.00002: The Hunt for a Snark: Spatially Resolved Imaging of Nucleation Centers in Ferroelectrics Sergei Kalinin, Stephen Jesse, Brian Rodriguez, Arthur Baddorf Ferroelectric polarization switching in non-volatile memory and high density data storage devices is governed by a number of nucleation centers that are necessary to account for experimentally observed low values of coercive fields. Despite 50 years of extensive research addressing the role of conductivity, surface dead layers, charge injection, and other factors, the microstructural origins of the Landauer paradox (switching fields correspond to implausibly large nucleation activation energies) are still a mystery. Here, Switching Spectroscopy Piezoresponse Force Microscopy (SS-PFM) is developed as a quantitative tool for real-space mapping of imprint, coercive bias, remanent and saturation responses, work of switching, and nucleation biases in ferroelectrics. Several examples of switching behavior in low dimensional ferroelectrics are presented, including (a) pinning at grain boundaries in polycrystalline PZT, (b) non-uniform work of switching in ferroelectric nanodots and (c) switching in the vicinity of topographic defects. The ``abnormal'' hysteresis loops were observed in the vicinity of topographic defects in multiferroic thin films and PZT ceramics and attributed to the interaction of nascent domain with the strain field of the defect. The mapping of the spatial and energy distribution of Landauer switching centers is demonstrated. [Preview Abstract] |
Monday, March 5, 2007 8:48AM - 9:00AM |
A39.00003: Probing Ferroelectricity in Barium Titanate Nanorods by Optical Spectroscopy Kin Fai Mak, Daohua Song, Joanna Atkin, Yuanbing Mao, Stanislaus S. Wang, Tony F. Heinz Finite-size effects in ferroelectric materials have attracted interest for both fundamental reasons and applications. In particular, previous studies have examined the role of film thickness and grain size on the ferroelectric properties of the well-known BaTiO$_{3}$ system. In this work we examine chemically synthesized nanorods of BaTiO$_{3 }$to probe ferroelectricity in well-controlled samples. The ferroelectric response in nanorods of 30-100 nm diameter and micron length was measured using optical second-harmonic generation (SHG) and Raman spectroscopy. SHG serves as a non-contact method of identifying the ferroelectric-paraelectric phase transition since the process is allowed only for the non-centrosymmetric ferroelectric phase; Raman spectroscopy provides a complementary method of probing structure relevant for the phase transition. Both the SHG and Raman signals show evidence of the expected ferroelectric to paraelectric phase transition at temperature above the bulk transition temperature. Results obtained both for ensemble samples and for many individual nanorods will be presented and compared. [Preview Abstract] |
Monday, March 5, 2007 9:00AM - 9:12AM |
A39.00004: Ferroelectric domain structures near the morphotorpic phase boundary in the piezoelectric material Pb(Zr$_{1-x}$Ti$_{x})$O$_{3}$ T. Asada, Y. Koyama In the simple perovskite oxide Pb(Zr$_{1-x}$Ti$_{x})$O$_{3}$, an\textbf{ }excellent piezoelectric response was obtained in the vicinity of a morphotropic phase boundary (MPB) between the ferroelectric monoclinic (F$_{M})$ and rhombohedral (F$_{R})$ phases. To understand the origin of the excellent response, we have investigated the detailed features of ferroelectric domain structures near the MPB in PZT by transmission electron microscopy. In the F$_{M}$ side of the MPB, as a result, there were two types of domain structures at room temperature. On the other hand, a usual domain structure having the 109\r{ } and 180\r{ } boundaries existed at room temperature in the F$_{R}$ side. The notable feature is that each domain in the F$_{M}$ and F$_{R}$ domain structures near MPB can be identified as an aggregation of nanometer-sized domains with an average size of about 10 nm. Based on this feature, we propose a new concept of an aggregation-type domain structure for ferroelectric domain structures near the MPB. [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:24AM |
A39.00005: Ferroelectric Phase transition in (1-x)Pb(Fe$_{2/3}$W$_{1/3})$O$_{3}$-xPbTiO$_{3}$ solid solutions thin films Ashok Kumar, N.M. Murarai, Ram S. Katiyar We have deposited thin films of (1-x)Pb(Fe$_{2/3}$W$_{1/3})$O$_{3}$-xPbTiO$_{3}$ (PFWT) on Pt/Si substrates. The metamorphic phase diagram of PFWT solid solution indicates that it changes from natural relaxor to an ordered ferroelectric state above x = 0.33 of lead titanate concentration. The microstructure and surface morphology were investigated using SEM and AFM techniques that indicated surface roughness of 10-15 nm with particle size of $\sim $ 30-50 nm. The dielectric relaxation studies in these films were carried out measured in the temperature range of 100K-650K and the frequency range of 100Hz-1MHz. The ferroelectric phase transition was found at 575K for all frequencies. The Relaxation indication coefficient ($\gamma \sim $1.30) was estimated from a linear fit of the modified Curie-Weiss law and results suggested a long range ordering. The temperature dependant micro Raman studies revealed a ferroelectric phase transition from tetragonal to cubic phase above 575K. The polarization hysteresis curve at room temperature illustrated a ferroelectric nature of the material having ramanat polarization (P$_{r})$ to be 3$\mu $C/cm$^{2}$ and the saturation polarization (P$_{s})$ 30$\mu $C/cm$^{2}$. [Preview Abstract] |
Monday, March 5, 2007 9:24AM - 9:36AM |
A39.00006: Near-field second-harmonic imaging of ferroelectric domain structure of YMnO$_3$ C.C. Neacsu, B.B. van Aken, M. Fiebig, M.B. Raschke Ferroelectrics have attracted much recent interest for applications in, e.g., data storage devices. The ferroelectric domain formation and order in a single crystal is the result of a subtle interplay between electric field and the elastic and domain wall energies to minimize the total free energy of the system. This makes the prediction of domain size and shape a priori difficult. Due to its symmetry selectivity optical second-harmonic generation (SHG) is sensitive with respect to the ferroelectric order in a system. For spatially resolved imaging we combine it with tip-enhanced near-field optical microscopy providing resolution down to 10 nm. Unpoled single-crystalline multiferroic YMnO$_{3}$ with the order parameter along the hexagonal z-axis and in the surface plane was probed. With the incident laser field polarized parallel to the tip axis we selectively access the nonlinear tensor component $\chi_{zxx}$ of the sample. The imaging contrast arises from the local interference between the induced SH-polarization in the sample and the SH reference field of the tip apex itself. The domains are found to be anisotropically elongated along the hexagonal axis with dimensions of several 100 nm. [Preview Abstract] |
Monday, March 5, 2007 9:36AM - 9:48AM |
A39.00007: ABSTRACT HAS BEEN MOVED TO A39.00001 |
Monday, March 5, 2007 9:48AM - 10:00AM |
A39.00008: Nanoscale 180 Degree Stripe Domains in PbTiO$_{3}$ Films Carol Thompson, D. D. Fong, G. B. Stephenson, J. A. Eastman, P. H. Fuoss, F. Jiang, S. K. Streiffer, R. -W. Wang, K. Latifi Nanoscale 180 degree stripe domains have been found to be the equilibrium structure of ultrathin ferroelectric films on insulating substrates [Fong, D. D. \textit{et al.}, \textit{Science }\textbf{304}, 1650 (2004)]. Here we report a study of the morphology of these stripe domains in PbTiO$_{3}$ films using room-temperature AFM imaging and high-temperature synchrotron x-ray scattering. The stripes can be aligned with surface steps, or with the underlying crystal lattice, depending upon film thickness and temperature. These equilibrium domains provide a new class of electrically active, controllable ``soft'' patterns in a hard material that are promising for self-assembly of oppositely charged adsorbates on sub-lithographic length scales. [Preview Abstract] |
Monday, March 5, 2007 10:00AM - 10:12AM |
A39.00009: Local decomposition of solid solutions at the ferroelectric-antiferroelectric interphase boundaries and formation of nanostructures in the process of phase transformation V.L. Sobolev, V.M. Ishchuk, Z.A. Samoylenko, N.A. Spiridonov Local decomposition of (PbLa)(ZrTi)O$_{3}$ near the interphase boundaries separating domains of coexisting FE and AFE phases was investigated. We studied the local decomposition kinetics in the process of aging of samples quenched to room temperature from the paraelectric phase. Mechanisms defining the kinetics of the attainment of the equilibrium state of coexisting FE and AFE domains (with sizes of 20 to 30 \textit{nm}) are analyzed. There are two main mechanisms determining the establishing of the equilibrium inhomogeneous chemical composition. The slower mechanism is the diffusion of the oxygen vacancies the nonequilibrium concentration of which was created during the annealing at T $>$ T$_{c}$. The faster process is due to the cation diffusion caused by the local mechanical stresses at the interphase boundaries. The sizes of segregates formed at the interphase boundaries are from 8 to 15 \textit{nm}. [Preview Abstract] |
Monday, March 5, 2007 10:12AM - 10:24AM |
A39.00010: Quasi-amorphous pyro- and piezo- electric SrTiO3. David Ehre, Vera Lyahovitskaya, Igor Lubomirsky Recent publications about quasi-amorphous BaTiO3 materials have demonstrated that non-crystalline ionic solids can exhibit pyro- and piezo- electricity. This posed a question whether the quasi-amorphous state is unique to BaTiO3 or other compounds can form non-crystalline polar phases. We report that pulling through a temperature gradient converts amorphous thin ($<$100 nm) films of SrTiO3 into a pyro- and piezoelectric phase, which is nevertheless non-crystalline according to XRD and SEM. Thus SrTiO3 may form a quasi-amorphous phase. This implies that: (1) the quasi-amorphous state is not unique to BaTiO3 but other compounds may form similar phases; (2) polarity of a compound in a quasi-amorphous phase is not related directly to the polarity of this compound in a crystalline form. In this view, one may expect that other quasi-amorphous phases will be found. Owing to the simplicity of their preparation, quasi-amorphous materials are very promising for future pyroelectric and piezoelectric devices that can be integrated with modern semiconductor technology. [Preview Abstract] |
Monday, March 5, 2007 10:24AM - 10:36AM |
A39.00011: Electroactive Properties of Potentially Ferroelectric Cyanopolymer Systems Matt Poulsen, Stephen Ducharme, James Takacs, Sahadeva Reddy, V.M. Fridkin Piezoelectric, pyroelectric, and potentially ferroelectric behavior have been observed in newly synthesized cyanopolymer systems. These systems are chemical analogs to the well known ferroelectric polymer poly(vinylidene fluoride), PVDF. Various chemical groups have been used to replace the electronegative fluorine and electropositive hydrogen atoms found in PVDF. This substitution maintains the polar nature of the all-trans conformation while increasing the amphiphilic nature of the said polymers. The increased amphiphilic nature of the polymers allows for the employment of the Langmuir-Blodgett technique in the fabrication of ultra-thin (less than 10 nm) polymer films. These cyanopolymers include poly(methyl vinylidene cyanide) and several of its copolymers. Piezoelectricity and pyroelectricity have been clearly observed in several of these systems. In addition, evidence for polarization reversal suggests that some members of this family of polymers may be ferroelectric in nature. Piezoelectric, pyroelectric, and ferroelectric properties make these cyanopolymers a promising new class of materials for use in electromechanical transducers, nonvolatile memories, and infrared imaging. [Preview Abstract] |
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