Scholarly Work - Physics
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Item Ferroelectric Transition in 70/30 VF2 /TrFE Copolymer Studied by Deuteron nmr(1989-04-01) Perry, Carole; Dratz, Edward A.; Ke, Yong; Schmidt, V. Hugo; Kometani, J.M.; Cais, R.E.Deuteron pulse nuclear magnetic resonance (NMR) spectra and spin-spin (T2) and spin-lattice (T1) relaxation times were measured between 20 and 140°C for a 70/30 mol% random copolymer of deuterated vinylidene fluoride (VF2) and normal trifluoroethylene (TrFE). These “powder” spectra were simulated by the Vold procedure and were dePaked to aid in studying the molecular motions. The spectra show that the ferroelectric (FE) transition occurs between 40 and 140°C with large thermal hysteresis. The dePaked spectra at 140°C are consistent with a dynamically disordered 3/1 helical structure.Item Dielectric Relaxation Mechanism for Proton Glass(1988-02-01) Schmidt, V. HugoDielectric relaxation of proton glasses is controlled by 0-H…0 proton intrabond hopping responsible for ‘Takagi’ HPO4 and H3PO4 intrinsic defect diffusion. The diffusion path has a one-dimensional fractal topology. The defects diffuse in a potential which also has a fractal nature, giving a barrier height distribution leading to a wide spread in dielectric relaxation times at low temperature. Expressions for dielectric relaxation and ac susceptibility are derived, and their fit to experimental results is briefly discussed.Item Frequency Dependence and Anisotropy of the Glass Transition Tg of Rb0.52(ND4)0.48D2PO4(1988-03-01) Stankowski, Jan; Trybula, Zbigniew; Schmidt, V. HugoThe frequency dependence of the glass transition temperature Tg has been calculed from the Vogel-Fulcher law using dielectric data obtained in the 102 Hz to 1010Hz region. The best fit was obtained with 1nfo= 29 and To= 38 K. The anisotropy of Tg predicted recently by theory has been observed.Item Comment on ‘The Role of Hydrogen Bonds in Antiferroelectricity of NH 4 H 2 PO 4 ’(1987-10-15) Schmidt, V. HugoFrom a microscopic viewpoint on the role of two kinds of hydrogen bonds, antiferroelectric phase transition in NH 4 H 2 PO 4 is re-examined. The role played by the protons of NH 4 ions is explicitely taken into account, and it is shown that the hydrogen bonding effect of NH 4 ions with neighbouring oxygens may be renormalized into the effective antiferroelectric interaction between protons which form the network of hydrogen bonds connecting PO 4 groups.Item Raman Scattering Study of Rb1-x(ND4)D2PO4 Mixed Crystal.(1987-12) Martinez, J.L.; Agullo-Rueda, F.; Schmidt, V. HugoRaman-scattering spectra of a 71.4% deuterated crystal of Rb0.52(ND4)0.48D2PO4 were studied in a wide range of temperatures down to 5 K. At low temperatures the system forms a so-called glass state, with no long range order transition to either a ferroelectric or antiferroelectric phase.We have concentrated our study on the vibrations related to the internal modes of the molecular groups (phosphate and ammonium). Special attention is focused on the v2 (symmetric deformation mode) of the PO4 and the libration mode of the ammonia, because they are very sensitive to the ordering of the protons, and to the ferroelectric- or antiferroelectric-like ordering for the former and the glass-like arrangement for the latter.Item Ferroelectric Research at the University of Washington During the Period 1955-70(1987-08) Uehling, Edwin A.; Bjorkstam, John L.; Schmidt, V. HugoRaman-scattering spectra of a 71.4% deuterated crystal of Rb0.52(ND4)0.48D2PO4 were studied in a wide range of temperatures down to 5 K. At low temperatures the system forms a so-called glass state, with no long range order transition to either a ferroelectric or antiferroelectric phase.We have concentrated our study on the vibrations related to the internal modes of the molecular groups (phosphate and ammonium). Special attention is focused on the v2 (symmetric deformation mode) of the PO4 and the libration mode of the ammonia, because they are very sensitive to the ordering of the protons, and to the ferroelectric- or antiferroelectric-like ordering for the former and the glass-like arrangement for the latter.Item Review of NMR Studies of Piezoelectric Polymers(1987-06) Schmidt, V. HugoNuclear magnetic resonance (NMR) investigations of the piezoelectric polymer poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoroethylene (TrFE) in their various crystalline phases are reviewed, and suggestions for future work are made.Item Dielectric measurements of the proton-glass state in Rb0.65(NH4)0.35H2AsO4(1988-09) Trybuła, Z.; Schmidt, V. Hugo; Drumheller, John E.; He, Di; Li, ZhouningDielectric measurements of the Rb1−x/emph>(NH4)xH2AsO4 (x=0.35) mixed crystals in the a and c tetragonal directions in the temperature range from 3 to 300 K are reported. Below Tg a dielectric dispersion of ε’(T) and ε’’(T) in the applied frequency range from 1 Hz to 30 kHz was observed. A small anisotropy of the proton-glass transition temperature Tg was detected, but we did not find the large anisotropy reported by J. Kim, N. Kim, and K. Lee [J. Phys. C 21, L-663 (1988)].Item Cs 133 Nuclear Magnetic Resonance Study of One-Dimensional Fluctuations in CsH 2 PO 4 and Its Ferroelectric and Antiferroelectric Transitions at High Pressure(1989-02) Schuele, Paul J.; Schmidt, V. HugoPressure and temperature effects on the one dimensional (1D) and higher-dimensionality correlations associated with the ferroelectric and antiferroelectric phase transitions in cesium dihydrogen phosphate were studied by means of the Cs133 nuclear magnetic resonance (NMR) spin-lattice relaxation time T1. We measured T1 at 6.5 MHz at temperatures down to the ferroelectric (FE) Curie point TC at 1 bar and at 1.5 and 3.0 kbar, down to the triple point Tt=124.6 K at 3.3 kbar, and down to the antiferroelectric (AFE) Néel point TN at 3.6 kbar. With decreasing temperature, T1 first decreases exponentially due to 1D fluctuations associated with the Jb interactions in disordered hydrogen-bonded chains running along b. As the temperature falls further, T1 then decreases linearly as the Jc interaction between these chains in hydrogen-bonded planes comes into play. From these results and the known pressure derivatives of TC and TN, we calculated pressure dependences for Jb, Jc, and for the interplanar interaction Ja. At 3.3 kbar Ja changes sign, so the plane stacking becomes AFE instead of FE. Above 8.9 kbar, where Jc extrapolates to zero, a new AFE phase with a checkerboard arrangement of FE b chains is predicted.Item Deuteron NMR and a Model for Phase Transitions in Monoclinic RbD 2 PO 4 .(1989-02) Jarh, O.; Dolinšek, J.; Topič, B.; Žekš, B.; Blinc, Robert; Schmidt, V. Hugo; Shuvalov, L. A.; Baranov, A. I.The quadrupole-perturbed deuteron NMR spectra and spin-lattice relaxation times of monoclinic RbD2PO4 have been measured and the electric-field-gradient tensors at the deuteron sites have been determined in phase I at 110 °C, phase III at 80 °C, and phase III at 40 °C. The results are incompatible with a location of the D(2) and D(3) deuterons in the center of the corresponding H bonds. They show that these deuterons are disordered between two off-center sites in phases I and II, whereas they are ordered in phases III and IV. A four-sublattice model accounting for all four phase transitions in monoclinic RbD2PO4 is proposed.