Browsing by Author "Uehling, Edwin A."

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Deuteron Intrabond Motion and Ferroelectricity in KD2PO4
(American Physical Society, 1964-01) Silsbee, Henry; Uehling, Edwin A.; Schmidt, V. Hugo
The Slater theory of the ferroelectric phase transition in KH2PO4 type crystals as modified by Takagi and extended by Senko is examined again in the light of recent measurements of parameters made on KD2PO4. Making full use of the measurements, and assigning an appropriate numerical value to one adjustable parameter which is not independently measured, the theory gives a nearly correct description of the shape of the spontaneous polarization curve. Also the value obtained for the Curie constant is probably satisfactory in view of limitations of the model and uncertainty of the high-temperature experimental data. The theory fails, however, in at least one important respect; the transition entropy is overestimated. This and other discrepancies are discussed briefly.
Ferroelectric Research at the University of Washington During the Period 1955-70
(1987-08) Uehling, Edwin A.; Bjorkstam, John L.; Schmidt, V. Hugo
Raman-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.
Random Motion of Deuterons in KD2PO4
(American Physical Society, 1969-04) Schmidt, V. Hugo; Uehling, Edwin A.
Magnetic resonance studies of the deuteron in KD2PO4 have been conducted which show the existence of deuteron jumping between and within hydrogen bonds. The experimental results help to explain electrical conductivity and ferroelectric phenomena in crystals of this type. Pulse magnetic resonance experiments show that the lifetime TXY against deuteron jumping between X- and Y-oriented hydrogen bonds is 15 msec at 70°C with a jump activation energy of approximately 0.58 ev. The c-axis electrical conductivity of KD2PO4 is found to have the same activation energy, with a value of 1.16×10−10 (ohmcm)−1 at 25°C. The Δm=1(P1) and Δm=2(P2) deuteron spin-lattice relaxation transition probabilities due to X−Y jumps have been calculated from the known values of TXY and the electric field gradient tensors at X and Y deuteron sites. Their magnitudes and the dependences of these magnitudes on magnetic field, temperature, and orientation are in good agreement with experiment. Further measurements of P1 and P2 separately give a component of transition probability proportional to exp(0.078 ev/kT) and independent of magnetic field. The orientation dependences of P1 and P2 for this component indicate quadrupolar relaxation due to deuteron jumps along hydrogen bonds, with a jump time of order 10−11 sec at 215°K. The existence of intrabond jumps governed by an activation energy is shown to be consistent with the Slater theory of KH2PO4 as modified by Takagi.