Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N20: Focus Session: Ferroelectrics |
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Sponsoring Units: FIAP DMP Chair: Nicola Spaldin, UC-Santa Barbara Room: LACC 407 |
Wednesday, March 23, 2005 8:00AM - 8:36AM |
N20.00001: Beyond PZT: Novel Perovskite Alloys and More Invited Speaker: The formation of a morphotropic phase boundary (MPB) is crucial for obtaining good piezoelectric performances in PZT and perovskite relaxors. In these systems the MPB occurs between tetragonal and rhombohedral phases. These phases are driven by mostly A-site ferroelectric instabilities but, as we will show, it is the energetics of the B-site displacement that tips the balance between rhombohedral and tetragonal ground states. We have analyzed several perovskitic compounds and classified them according to four different classes: (1) stable cubic, e.g. BaZrO$_3$, (2) B-site active, e.g. BaTiO$_3$, (3) purely A-site active, e.g. PbZrO$_3$, and (4) cooperative systems, e.g. PbTiO$_3$. From the analysis of the interplay between structural instabilities we derived strategies to design novel compounds for piezoelectric applications in the class of scandates and niobates. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 8:48AM |
N20.00002: Theoretical prediction of new high-performance lead-free ferroelectrics Pio Baettig, Charles Schelle, Nicola Spaldin, Richard LeSar, Umesh Waghmare We predict the occurence of large ferroelectric polarization and piezoelectricity in the hypothetical perovskite-structure oxides, bismuth aluminate (BiAlO$_{3}$) and bismuth gallate (BiGaO$_{3}$), using density functional theory within the local density approximation. We show that BiGaO$_{3}$ will have a similar structure to PbTiO$_{3}$, although with much stronger tetragonal distortion and therefore improved ferroelectric properties. Likewise, BiAlO$_{3}$ shares structural characteristics with antiferrodistortive PbZrO$_{3}$, but it is also a ferroelectric with large polarization. Therefore we propose the Bi(Al,Ga)O$_{3}$ system as a replacement for the widely used piezoelectric sensor, Pb(Zr,Ti)O$_{3}$ (PZT) that will avoid the environmental toxicity problems of lead-based compounds. Finally we show that, in both BiAlO$_{3}$ and BiGaO$_{3}$, the large distortions from the prototypical cubic structure are driven by the stereochemical activity of the Bi lone pair. [Preview Abstract] |
Wednesday, March 23, 2005 8:48AM - 9:00AM |
N20.00003: Magneto-electric coupling in hexagonal RMnO3 Thomas Palstra, Agung Nugroho, Gwilherm Nenert, Umut Adem, Yang Ren The hexagonal RMnO3 exhibit much higher magnetic and ferroelectric ordering temperatures, T(N) = 75 K and T(FE) = 930 K than the orthorhombic RMnO3 with an incommensurate antiferromagnetic ordering below 40K. However, the coupling between the magnetic and electric order is very weak. We have investigated the origin of the electric order by high temperature x-ray diffraction using high energy synchrotron radiation. We discuss the change in symmetry at the ferro-electric ordering temperature, which is a few hundred degrees below the tripling of the unit cell. Additionally, we have used magneto-capacitance measurements to study the coupling between magnetic and electric order. We report results on hexagonal RMnO3 and also substitutions on the rare earth- and the Mn-site. [Preview Abstract] |
Wednesday, March 23, 2005 9:00AM - 9:12AM |
N20.00004: High-pressure Raman scattering and x-ray diffraction study of relaxor ferroelectric 0.96Pb(Zn1/3Nb2/3)O3-0.04PbTiO3 Muhtar Ahart, Ronald E. Cohen, Russell J. Hemley High-pressure Raman scattering and x-ray diffraction of lead zinc niobate-lead titanate (PZN-4{\%}PT) solid solutions were measured from ambient to 13 GPa. All of the Raman peaks are broad due to the disorder of Zn$^{2+}$ and Nb$^{5+ }$on the B site of the perovskite structure. No obvious soft-phonon-mode feature was observed. High-pressure x-ray diffraction was used to determine the bulk modulus and also revealed diffuse scattering near the Bragg peaks. The diffuse x-ray scattering decreases on compression and disappears at 5 GPa. Changes in both the Raman spectra and the diffuse scattering reflect suppression of the local distortion in the material on compression. The results can be understood in terms continuous changes in the local potential surfaces with increasing pressure. Pressure causes the ferroelectric well-depths to decrease, which causes a continuous transition from ferroelectric to relaxor to paraelectric. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:24AM |
N20.00005: BaTiO$_3$ and Quantum Monte Carlo: Lattice Constants Lucas K. Wagner, Lubos Mitas Transition metal oxides are well-known to be difficult to describe using standard first principles techniques like Density Functional Theory. For example, straightforward application of generalized gradient and local density approximations make errors of about 3\% on the primitive cell volume of BaTiO$_3$ in the tetragonal phase, one of the simplest ferroelectrics. Since the ferroelectric properties are extremely sensitive on lattice constants and structural parameters one has to either adjust the functionals or set the lattice constant to experiment with a resulting error in phase transition temperature. We show progress on calculations using Quantum Monte Carlo (QMC) to predict the static properties of BaTiO$_3$, using correlated sampling to overcome the statistical error on these extremely small energy differences. Preliminary results indicate that QMC is able to predict the tetragonal volume to less than 1\%(the error bars) without experimental input, as well as describe the band gap with a good agreement with experiment. [Preview Abstract] |
Wednesday, March 23, 2005 9:24AM - 9:36AM |
N20.00006: Topological Nature of Polarization and Charge Pumping in Ferroelectrics Shigeki Onoda, Shuichi Murakami, Naoto Nagaosa Dielectric properties of insulators have been one of the most important subjects in condensed matter physics. Recently, the quantum theory of electric polarization in insulators has been developed in terms of the Berry phase, which fully takes account of the covalency. However, the intuitive picture is hidden in sophisticated first-principle band calculations. Here, we provide a clear and comprehensive view on the quantum theory of polarization for two-band models: In the space of external parameters such as displacements of atomic or molecular orbitals, pressure, and electric field, a vector field representing an infinitesimal change of polarization due to that of the parameters is dominantly characterized by a string. This string is a trajectory of the band crossing points and fully describes the singularity of the vector field. The total flux of the string and thus the charge pumped during a cyclic adiabatic change of the external parameters are quantized to an integer multiplied by the electronic charge. Applications of this picture to various organic ferroelectrics and BaTiO$_3$ are discussed. [Preview Abstract] |
Wednesday, March 23, 2005 9:36AM - 9:48AM |
N20.00007: Temperature dependent electrical properties of the epitaxial junction between Nb:SrTiO$_{3}$ and magnetite (Fe$_{3}$O$_{4}$) S.B. Ogale, Darshan C. Kundaliya, S. Dhar, S.R. Shinde, T. Venkatesan Epitaxial films of magnetite (Fe$_{3}$O$_{4})$ were grown on single crystal (001) Nb:SrTiO$_{3}$ substrates by pulsed laser deposition. The films were characterized by x-ray diffraction, Rutherford backscattering-ion channeling spectrometry, SQUID, and four probe resistivity measurements. The growth conditions were optimized to achieve good crystallinity as well as the expected transport and magnetic characteristics of the Verwey transition at 120 K. Such junctions were then examined for the temperature dependent current-voltage (I-V) characteristics, which exhibited a non-linear behavior and an interesting non-monotonic temperature dependence. The data were also recorded in magnetic field up to 5 Tesla. These data were analyzed within the framework of a band description of transport across the interface between dissimilar semiconducting oxides and the fitting parameters were extracted. The temperature evolution of these parameters showed systematic trends, with interesting changes near the Verwey transition. These data are analyzed based on the electronic density of states$^{1}$ and the nature of transport$^{2,3}$ in magnetite. 1. Z. Zhang et al. Phys. Rev. B 44, 13319 (1991), 2. D. Ihle et al. J. Phys. C : Solid State Phys. 19, 5239 (1986), 3. S. B. Ogale et al. Phys. Rev. B 57, 7823 (1998). [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N20.00008: Polarization enhancement and heterointerfacial coupling in artificial perovskite superlattices Ho Nyung Lee, Hans Christen, Matthew Chisholm, Christopher Rouleau, Douglas Lowndes Bi- and tri-color superlattices comprised of BaTiO$_3$, SrTiO$_3$, and CaTiO$_3$ with compositionally-abrupt interfaces have been grown on atomically-flat SrRuO$_3$ bottom electrodes on (001) SrTiO$_3$ single crystals by pulsed laser deposition. These superlattices provide additional freedom in tuning the average lattice parameter and the structure’s physical properties. We found that locally asymmetric heterointerfaces (TiO$_6$- octahedra bound by different A-site cations) play a crucial role in the polarization enhancement due to elastic and electrostatic couplings at the interfaces. Such subtle effects, especially in tri-color superlattices, can be attributed to the broken inversion symmetry, although the effects are sometimes weak. A strong polarization enhancement is achieved by the proper balancing between two competing requirements: the ferroelectric layers must thick enough to contain a sufficient amount of non-interfacial TiO6 octahedra, but thin enough to remain fully strained. For a superlattice, this produces a maximum polarization as much as 50\% higher than that of a BaTiO$_3$ single film. Research sponsored by the U.S. Department of Energy under contract with the Oak Ridge National Laboratory, managed by UT-Battelle, LLC, as part of a BES NSET initiative. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N20.00009: Phonons in SrTiO$_3$ under finite electric fields Ivan Naumov, Huaxiang Fu It has been nearly 40 years since Worlock and Fleury discovered by means of Raman scattering that {\it under finite electric fields} the transverse-optic (TO) phonons in SrTiO$_3$ exhibit a striking increase in frequency---by more than 400\% of its zero-field value---when a very small field of 12 kV/cm is applied [1]. Despite its obvious importance, this giant field- induced shift of phonon frequency has not thus far been independently investigated via the density-functional theory (DFT). Here, we propose an approach within the DFT theory to determine the phonon structure of infinite solids under finite electric fields. We applied this approach to SrTiO$_3$ and found a giant shift in TO frequencies, in accordance with the observations [1]. Our calculations further predict other unusual properties that occur under finite electric fields, that is, an anomalous piezoelectric response and large dielectric tunability. (This work was supported by ONR). [1] J.M. Worlock and P.A. Fleury, Phys. Rev. Lett. {\bf 19}, 1176 (1967). [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N20.00010: Low-Temperature Transitions in Nanograin Barium Titanate Y-D. Wang, W. Dmowski, X-H. Wang, X-Y. Deng, L-T. Li, I-W. Chen Nanograin ferroelectrics suffer from diffraction limit that causes line broadening making it difficult to ascertain phase transitions. This, however, may be overcome by analyzing the temperature dependence of line shapes. We investigated the successive low-temperature transitions from tetragonal to orthorhombic to rhombohedral symmetries in nanograin BaTiO$_{3}$ ceramics using high resolution diffraction and Raman local probe. The existence of orthorhombic and rhombohedral symmetries over a coherent length of the order of grain size, as small as 50 nm, was established by high-resolution diffraction. The coexistence of different symmetries and reduced distortions over different length scales was also evident from both diffraction and Raman local probe. These results explain the broad and rather weak dielectric anomalies associated with these ceramics, which will become important for future dielectric applications in ultrathin multilayer electronic components. [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 10:36AM |
N20.00011: Pressure-induced anomalous enhancement of piezoelectricity and polarization rotation via an unexpected monoclinic phase of PbTiO$_3$ Zhigang Wu, Ronald E. Cohen Pressure-induced phase transitions and piezoelectricity of PbTiO$_3$ were studied using the {\it ab initio\ } density functional perturbation theory (ABINIT4.3.3). A tetragonal ($P4mm$) to monoclinic ($Pm$) phase transition occurs at 9 GPa, while this monoclinic phase transforms into paraelectric cubic phase at 22 GPa. The monoclinic ($Pm$) phase acts as the pressure-induced structural bridge between the tetragonal ($P4mm$) and rhombohedral ($R3m$) phases since its polarization rotates continuously in the pseudocubic ($\bar{1}$10) plane from the [001] towards the [111] pseudocubic directions. Under hydrostatic pressure, the enthalpy ($H = E + PV$) difference between the tetragonal and rhombohedral phases becomes tiny, and the polarization rotation via the monoclinic phase is possible, which results in huge enhancement of the piezelectric constant $e_{15}$, very similar to relaxor PZT. At 9 GPa, the spontaneous polarization is roughly half of that at 0 GPa, while the piezoelectric coefficient $d_{15}$ is comparable in magnitude to $d_{33}$ of relaxors PMN-PT and PZN-PT. [Preview Abstract] |
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N20.00012: Structural study of thin-film PbTiO$_3$-CoFe$_2$O$_4$ composition spreads Leonid A. Bendersky, M. Murakami, I. Takeuchi Multiferroic materials exhibiting magnetoelectric (ME) effects are of great interest for novel devices. In multiphase systems, the ME effect arises from the elastic interaction of ferromagnetic and ferroelectric phases. Recently we studied properties and structures of multiferroic PbTiO$_{3}$ (PTO) and CoFe$_{2}$O$_{4}$ (CFO) thin films produced by a composition-spread technique. The compositional spread was achieved by PLD of a superlattice of pure PTO and CFO. Here we report results of cross-sectional TEM studies, which can be summarized as following: a. For all compositions the microstuctures yielded pseudo-binary two phases equilibrium of PTO and CFO, and the phases are epitaxial to each other and to a MgO substrate; b. Morphology of the phases strongly depends on a thickness of the deposited superlattice; c.The most pronounced ME effect was found for a pancake-like morphology; d.Diffusional re-arrangement of layers during the deposition results in the solubility of CFO in PTO, which drastically reduces ferroelectric Curie temperature of PTO. [Preview Abstract] |
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