Scholarly Work - Physics
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/3458
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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.Item ND4 Deuteron NMR and the Smearing of the Glass Transition in Rb1-x(ND4)xD2PO4(1988-05) Blinc, Robert; Dolinsek, J.; Schmidt, V. Hugo; Ailion, D.C.The broadening of the rotationally averaged ND4+ deuteron lines in Rb0.56(ND4)0.44D2PO4 due to the gradual "acid" deuteron freeze-out allows for a direct determination of the Edwards-Anderson pseudospin glass order parameter q far above the nominal glass transition temperature TG. The data provide strong evidence for a model where the basic difference between magnetic spin glasses and proton or deuteron pseudospin glasses is the presence of an inherent random field resulting from the substitutional disorder. This field acts as an ordering field conjugate to the pseudospin glass order parameter q and is responsible for the smearing of the deuteron glass transition.Item 17O NQR Study of the Antiferroelectric Phase Transition in TlH2PO4(1988) Seliger, J.; Zagar, V.; Blinc, Robert; Schmidt, V. HugoThe temperature dependence of the 1 7O NQR spectra in TlH2PO4 has been measured using a proton‐1 7 O nuclear quadrupole double resonance technique. The results show that the protons in the short one‐dimensionally linked O1–H1‐‐O1 and O2–H2‐‐O2hydrogen bonds are moving between two equilibrium sites above T c and freeze into one of the off‐center sites below T c . The protons in the asymmetric O3–H3‐‐O4hydrogen bonds are static and ordered above and below T c .Item Soft modes and proton tunneling in PbHPO4, squaric acid and KH2PO4, type ferroelectrics(1984-01) Blinc, Robert; Schmidt, V. HugoIt is pointed out that the huge observed differences in the soft mode frequencies of KH2PO4, PbHPO4, CsH2PO4 and squaric acid do not necessarily reflect a large difference in the proton 0—H———O tunneling frequencies but rather result from a difference in the short range correlations renormalizing the single proton O——H—O tunneling frequency.