Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session B20: Focus Session: Properties of Ferroelectrics and Relaxors |
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Sponsoring Units: DMP Chair: Hans Christen, Oak Ridge National Laboratory Room: Colorado Convention Center 105 |
Monday, March 5, 2007 11:15AM - 11:27AM |
B20.00001: Multiple-Scattering of Millimeter Waves in Random Dielectrics Dustin McIntosh, John A. Scales, L. D. Carr, Valentin Freilikher, Yu. P. Bliokh We investigate millimeter wave localization in random binary-layered dielectrics composed of sub-wavelength scatterers. We measure the broad-band phase-dependent reflection and transmission response of the system. The random dielectrics exhibit band gaps and transmission resonances, the hallmark of localization. The band gaps correspond to forbidden mode propagation; the resonances to effective cavities in the system. These cavities are associated with enhanced attenuation and slow light which we observe in both experiment and theory. These effects are a result of weak multiple-scattering by the layer boundaries due to the disorder in the dielectric stack. [Preview Abstract] |
Monday, March 5, 2007 11:27AM - 11:39AM |
B20.00002: Effect of Stress on Dielectric Loss Behavior in Ba0.7Sr0.3TiO3 Thin-Films Ricardo Zednik, Paul McIntyre, John Baniecki, Masatoshi Ishii, Kazuaki Kurihara, Kazunori Yamanaka We present the results of a systematic dielectric study of barium strontium titanate thin-film planar capacitors measured over a wide temperature range of 20 K to 575 K for frequencies between 1 kHz and 1 MHz. Sputter deposition on substrates with different thermal expansion coefficients were used to produce barium strontium titanate thin-films that differ only in their stress states. Over a narrow temperature range, near room temperature, the dielectric dispersion can be understood in terms of the phenomenological Curie-von Schweidler relationship (Universal Relaxation Law), with the complex permittivity following a power law dependence on frequency. However, outside this range, dielectric-loss peaks are observed in the temperature and frequency domains that can be closely fit to the Vogel-Fulcher expression used in describing relaxors. Additionally, the loss peaks shift with the stress state of the film. These observations suggest that the relaxor-like dielectric behavior of our barium strontium titanate thin-films may be affected by a possible phase transition. The dependence of the dielectric loss behavior on film stress in the Curie-von Schweidler and Vogel-Fulcher regimes will be contrasted and mechanisms for the observed stress dependent dielectric loss behavior discussed. [Preview Abstract] |
Monday, March 5, 2007 11:39AM - 11:51AM |
B20.00003: Ferroelectric Phase Transition Study of Coupling KTN Perovskites Oxide by Scanning Microwave Microscope. Shuogang Huang, Mark Reeves, Jennifer Sigman, David Norton, Hans Christen We used a scanning near field microwave microscope to determine the thin film dielectric properties of KTN near transition temperature. For solid solution K(NbxTa1-x)O3 thin film deposited on MgAl2O3 substrate a 1st order phase transition was observed and for KTN 1x1 super lattice two 2nd order phase transitions were observed. Then a finite element method simulation was applied to numerically calculate the dielectric constant of the samples in difference phases. The results show a strong consistent with the previous x-ray and capacitance measurements. [Preview Abstract] |
Monday, March 5, 2007 11:51AM - 12:27PM |
B20.00004: Interaction of Terahertz Radiation with Ferroelectrics Invited Speaker: Ferroelectric crystals have long been used as acoustic transducers and receivers. An extensive toolset has been developed for MHz-frequency acoustic wave generation, control, guidance, and readout. In recent years, an analogous toolset has been developed for terahertz wave transduction and detection. Femtosecond optical pulses irradiate ferroelectric crystals to generate responses in the 0.1-5 THz frequency range that are admixtures of electromagnetic and polar lattice vibrational excitations called phonon-polaritons. Spatiotemporal femtosecond pulse shaping may be used to generate additional optical pulses that arrive at specified times and sample locations for control and manipulation of the THz waves. Femtosecond laser machining may be used for fabrication of waveguides, resonators, and other structures that are integrated into the ferroelectric host crystal. Finally, real-space imaging of the THz fields can be executed with variably delayed femtosecond probe pulses, permitting direct visualization of THz wave spatial and temporal evolution. This ``polaritonics'' toolset enables multiplexed generation of arbitrary THz waveforms and use of the waveforms within the ferroelectric host crystal or after projection into free space or an adjacent medium. The polaritonics platform will be reviewed and several new developments and applications will be presented. These include spectroscopy of relaxor ferroelectrics, whose temperature-dependent dielectric responses in the GHz-THz regime reveal complex polarization dynamics on well separated fast and slow time scales; direct measurement of phonon-polariton lattice vibrational displacements through femtosecond time-resolved x-ray diffraction; generation of high polariton field amplitudes and pulse energies; use of large-amplitude polariton waves to drive nonlinear lattice vibrational responses; and enhancement of optical-to-THz conversion efficiency through a pseudo-phase-matching approach that circumvents the very large disparity between refractive index values at optical and THz frequencies. [Preview Abstract] |
Monday, March 5, 2007 12:27PM - 12:39PM |
B20.00005: Elastic constants and sound velocities in single crystal transition metal scandates Matthew G. Hilt, K.A. Pestka II, Jin H. So, J.D. Maynard An important effect on thin films deposited on substrates is the strain induced by lattice mismatch. Different perovskite structured transition metal scandates have similar a-axis lattice parameters but slightly different c-axis lattice parameters. By adjusting the transition metal content, the c-axis lattice parameter may be controlled, so that if these materials are used as substrates, lattice mismatch may be greatly reduced. To further match lattices dynamically, it is necessary to know the elastic constants of the scandate materials. However, only small single crystals of GdScO3, DyScO3, SmScO3, and NdScO3 have been fabricated. By using the small sample version of resonant ultrasound spectroscopy, we have determined the elastic constants and sound velocities for several transition metal scandates. [Preview Abstract] |
Monday, March 5, 2007 12:39PM - 12:51PM |
B20.00006: Additional mode of PbZr$_{x}$Ti$_{1-x}$O$_{3}$ films Chi Yat Yau, Relva Buchanan In addition to the phonon modes predicted by the selection rule, a phonon mode at 45 cm$^{-1}$ (lower than soft mode frequency) was observed in the first order Raman spectrum of ferroelectric PbZr$_{x}$Ti$_{1-x}$O$_{3}$ films with $x$ = 0 - 1. Thus, this additional mode is not a zone-center mode. Its existence in the first order spectrum is due to the zone folding in structures with strain, defect and disorder. This additional mode, like soft mode, also significantly downshifts as approaching the phase boundaries, e.g. at $x$ = 0.5 and 0.95, or with the grain size change. The similar change of the additional mode and the soft mode implies a strong interaction between the soft mode and the additional mode. [Preview Abstract] |
Monday, March 5, 2007 12:51PM - 1:03PM |
B20.00007: Phonon anomalies induced by polar nano-regions in a relaxor ferroelectric Guangyong Xu, Jinsheng Wen, Chris Stock, Peter Gehring Inelastic neutron scattering was used to measure both acoustic and optic phonons polarized along (110) (T2 mode) in the relaxor ferroelectric compound PZN-4.5PT. In the low temperature rhombohedral phase, a single domain state was achieved by cooling the single crystal sample under an external electric field of 2 kV/cm along the [111] direction. Phonon measurements were performed near the (2,2,0) and (2,-2,0) Bragg peaks. We have found that the TA2 phonon couples closely to the diffuse scattering, which arises from polar nano-regions in the system. With the redistribution of diffuse scattering under the external field (see Ref. 1), a clear hardening of TA2 mode was observed near the (2,2,0) Bragg peak, while the TA2 mode near (2,-2,0) Bragg peak softens significantly and becomes over-damped. Our results indicate local inhomogeneities such as the PNR can have direct and significant effects on the lattice dynamics and stability of the whole system. Ref. 1: ``Electric-field-induced redistribution of polar nano-regions in a relaxor ferroelectric'', Guangyong~Xu, Z.~Zhong, Y.~Bing, Z.-G.~Ye, and G.~Shirane, Nature Materials 5, 134, (2006). [Preview Abstract] |
Monday, March 5, 2007 1:03PM - 1:15PM |
B20.00008: Cubic ground state of field-cooled PbMg$_{1/3}$Nb$_{2/3}$O$_3$ Peter Gehring, Chris Stock, Guangyong Xu, Haosu Luo, Hu Cao, Jiefang Li, Dwight Viehland, Gen Shirane Neutron and x-ray diffraction techniques have been used to study the competing long and short-range polar order in the relaxor PbMg$_{1/3}$Nb$_{2/3}$O$_3$ (PMN) under the influence of an external [111]-oriented electric field. While the bulk unit cell remains cubic for electric fields up to 8\,kV/cm, a suppression of the diffuse scattering and a concomitant enhancement of the Bragg peak intensity is observed below $T_c=210$\,K, indicating a more ordered structure with increasing electric field yet an absence of a long-range ferroelectric ground state. The electric field strength has little effect on the diffuse scattering above $T_c$. The absence of hysteresis suggests that the ground state of PMN may not be a frozen glassy phase, but may be better understood in terms of random fields introduced through the presence of structural disorder. [Preview Abstract] |
Monday, March 5, 2007 1:15PM - 1:27PM |
B20.00009: Dielectric Spectroscopy and conductivity relaxation of PSN-PST relaxor thin films Margarita Correa, Natasan Baskaran, Ram Katiyar -abstract- Relaxor ferroelectric materials exhibit singular dielectric relaxation. They have large dielectric constant, high piezo and electrostrictive coefficients that make them useful for sensors, actuators and ferroelectric related devices. We have prepared PSN-PST relaxor thin films by pulsed laser deposition technique. Studies of dielectric properties, as a function of temperature (100-650K) and frequency (40 Hz --1 MHz) have shown that the materials have diffuse phase transition along with the frequency dispersion. The magnitude of dielectric constant and the temperature of maximum permitivitty (T$_{m})$ differ from those in the bulk form. However, its conductivity behavior follows similar trend in both bulk and thin film forms. The ac conductivity exhibits frequency independent plateau at lower frequencies followed by a dispersion region at higher frequencies. The observed dispersion of conductivity with frequency can be described by a power law $\sigma \left( \omega \right)=\sigma _{dc} +A\omega ^n$ with n$>$1. The unusual high n value is due to glassy like nature of the relaxor system and it is explained in terms of polaron assisted ionic mechanism. Detailed results will be presented. [Preview Abstract] |
Monday, March 5, 2007 1:27PM - 1:39PM |
B20.00010: Quantitative Huang-scattering analysis of local structure in the relaxor-based piezoelectric PZN-4.5{\%}PT Branton J. Campbell, Vayee Vue, Daniel Robertson, Stephan Rosenkranz, Peter Lee, Stine N. Anacona, Ray Osborn Polar nano-regions (PNR) in ferroelectric relaxor materials like Pb(Zn$_{1/3}$Nb$_{2/3})$O$_{3}$ and Pb(Mg$_{1/3}$Nb$_{2/3})$O$_{3}$ are of pressing applied interest due to their influence on the remarkable piezoelectric properties of their solid solutions with PbTiO$_{3}$. In the recent literature, x-ray and neutron single-crystal diffuse scattering techniques have been shown to provide qualitative insight into the local structure of these materials. Here, we present a quantitative three-dimensional Huang-scattering analysis of 80 keV x-ray single-crystal diffuse scattering data from PZN-4.5{\%}PT. [Preview Abstract] |
Monday, March 5, 2007 1:39PM - 1:51PM |
B20.00011: NMR Observation of Impurity-Pair Ordering in Weakly Disordered Solid Solutions David Ailion, Bostjan Zalar, Andrija Lebar Breaking of the average cubic symmetry in Li-doped potassium tantalate (K$_{1-x}$Li$_{x}$TaO$_{3})$ was observed with quadrupole-perturbed $^{7}$LiNMR at temperatures (150-400 K) far above the nominal glass transition temperature (80 K). The observed spectrum consists of contributions from both isolated Li ions (i.e., with no nearest neighbor Li) and from Li pairs. The isolated Li ions move among six equivalent off-center sites in a potential having cubic symmetry. These have zero average electric-field gradient and, hence, exhibit no quadrupole splitting. In addition, very low intensity, but well resolved, quadrupole satellites having a temperature-dependent splitting were observed. This splitting indicates that the various Li pair configurations are not all equally probable. These are the first observations of biased Li-ion ordering that persists in the paraelectric phase at temperatures high above the glass phase. [Preview Abstract] |
Monday, March 5, 2007 1:51PM - 2:03PM |
B20.00012: Local Basis Set Supercell Studies of (K,Na)NbO$_3$ Solid Solutions Ricardo Kagimura, Malliga Suewattana, David J. Singh We report density functional supercell calculations for (K,Na)NbO$_3$ perovskite solid solutions using the local basis SIESTA code. We did detailed comparisons of results for ferroelectric structures and vibrational frequencies obtained with SIESTA with those obtained using all-electron full potential LAPW calculations, and used these comparisons to establish compact but accurate choices of basis set and pseudopotentials for the SIESTA calculations. Supercell calculations using SIESTA are used to investigate the dependence of ferroelectric polarization and local structure on the K/Na ordering. This work was supported by the DOE ORNL LDRD program and the Office of Naval Research. [Preview Abstract] |
Monday, March 5, 2007 2:03PM - 2:15PM |
B20.00013: Effect of elastic strain and Sc dopant concentration-dependent cell volume on the electrical properties of Epitaxial (Ba,Sr)TiO$_{3}$ thin films WooYoung Park, CheolSeong Hwang, John D. Baniecki, Masatoshi Ishii, Kazuaki Kurihara, Kazunori Yamanaka We present the results of a systematic study of the correlation between dopant concentration-dependent elastic strain and dielectric properties in (Ba,Sr)TiO$_{3 }$films. For this work, undoped and Sc-doped (Ba,Sr)TiO$_{3}$ thin film capacitors epitaxially grown on SrTiO$_{3}$ substrate were prepared by a sputtering deposition method. Sc-doped BST capacitors exhibit significantly higher permittivity and lower leakage current density, but little effect on the loss tangent, as compared to nominally undoped BST capacitors. The Ti/(Ba+Sr) ratio of the films and Sc dopant concentration-dependent unit cell volume, as determined by x-ray sin$^{2}\psi $ analysis, are consistent with the preferential B-site occupancy of the Sc dopant. Furthermore, this work suggests that dopant concentration-dependent elastic strain as well as the 2D clamping effect of thin films on a thick substrate$^{1}$ must be considered to fully understand the dielectric behavior of perovskite titanate thin films. 1. N. A. Pertsev, A. G. Zembilgotov, and A. K. Tagantsev, Phys. Rev. Lett. 80, 1988 (1998) [Preview Abstract] |
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