Scholarly Work - Physics
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/3458
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Item Short-range interaction explanation of ferroelectric, antiferroelectric and proton glass behavior in pure RDP, ADP, and mixed RDP-ADP crystals respectively(1985-01) Schmidt, V. Hugo; Wang, J. T.; Schnackenberg, P. T.A unified model is presented for Rb1-x(NH4)xH2PO4 crystals over the whole range x=0 (RDP) to x=1 (ADP). Two short-range interactions are postulated. One is the Slater energy ε0 which is kept at the value for RDP for all x. The other is an interaction εa between two hydrogens in O-H...O bonds across an NH4+ ion from each other. It is responsible for the off-center positions observed for ammonium ions in the antiferroelectric phase of ADP. Its strength is assumed proportional to x. By minimizing the free energy, one finds a range of x for which no transition occurs, but instead proton glass behavior sets in. Fox x near 0 and 1 respectively, first-order ferroelectric and antiferroelectric transitions are predicted. Both phase boundaries are close to those observed experimentally.Item Anisotropy in Anomalies of Hypersound Velocity and Attenuation in Ferroelectric TSCC(1985-01) Hikita, T.; Wang, J. T.; Schnackenberg, P. T.; Schmidt, V. HugoFrom Brillouin shift and linewidth of longitudinal phonons propagating along the [100] and [001] directions of TSCC, the polarization relaxation time was calculated to be τ=3.1×10-12/(Tc-T) sec below the transition temperature Tc. The anomalies in the longitudinal phonons of the [010] propagation were carefully examined using an annealed crystal of excellent quality. No essential difference was observed between the velocities of a normal and high quality crystals. The relaxation time was deduced as a function of temperature from the observed anomalies in the velocity and linewidth. Spectra are observed for nearly forward scattering from the q\varparallel[010] phonons.Item Brillouin scattering near the ferroelectric phase transition in TSCC(1985-06) Hikita, T.; Schnackenberg, P. T.; Schmidt, V. HugoBrillouin spectra from longitudinal phonons in ferroelectric tris-sarcosine calcium chloride (TSCC) propagating along [100], [010] and [001] have been measured as functions of temperature. Large anomalies were found in the Brillouin shift and linewidth in the [100] and [001] phonons. These anomalies are interpreted as arising from the linear coupling of the polarization and phonons. From the the temperature where the linewidth is maximum, the relaxation time of the polarization fluctuations is estimated to be τ = 3.1×10−12/(Tc−T) sec, where Tc is the ferroelectric transition temperature. We also observed anomalies in Brillouin shift and linewidth of the [010] phonons which propagate along the ferroelectric axis. These anomalies are interpreted as coming from electrostrictive coupling. The energy relaxation time was estimated to be τE=2.5×10−10/(T−Tc) sec in the paraelectric (PE) phase and τE=1.0x10−9/(T−Tc) sec in the ferroelectric (FE) phase, by comparing our Brillouin results with those f the ultrasonic measurements.Item Dielectric studies of critical and tricritical phenomena in kdp and RD(1980-01) Schmidt, V. Hugo; Schnackenberg, P. T.; Western, Arthur B.; Baker, A. G.; Bacon, Charles R.; Crummett, W. P.Our method of obtaining and analyzing dielectric data for KDP is reviewed, which demonstrated that KDP has a tricritical point between two and three kbar pressure. We also describe our method for obtaining the critical exponents r and d. Our experimental results for KDP are summarized. New results are presented for RDP which agree with the conclusion of others that its transition is of second order at ambient pressure.