Browsing by Author "Blinc, Robert"

Now showing 1 - 7 of 7

17O NQR Study of the Antiferroelectric Phase Transition in TlH2PO4
(1988) Seliger, J.; Zagar, V.; Blinc, Robert; Schmidt, V. Hugo
The 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 .
75As nuclear quadrupole resonance in weakly substitutionally disordered Rb1‑x(NH4)xH2AsO4
(1994-07-11) Papantopoulos, G.; Papavassiliou, G.; Milia, F.; Schmidt, V. Hugo; Drumheller, John E.; Pinto, Nicholas J.; Blinc, Robert; Zalar, B.
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.
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.
Proton-glass state in K0.60(NH4)0.40H2AsO4 detected by dielectric measurements
(1990-10-01) Trybula, Zbigniew; Schmidt, V. Hugo; Drumheller, John E.; Blinc, Robert
Dielectric permittivity measurements of ε′a and ε''a in a K0.60(NH4)0.40H2AsO4 mixed crystal have been made in the temperature and frequency ranges 3–300 K and 1 Hz–30 kHz. We find proton-glass behavior in this material similar to that observed in the Rb1−x(NH4)xH2AsO4 and Rb1−x(NH4)xH2PO4 systems. Below Tg the dielectric dispersion characteristics of the freezing of the polarization are well described phenomenologically by the Vogel-Fulcher law. The best fit gives the Vogel-Fulcher temperature T0=5.4 K, the attempt frequency ν0=2.5×1013 Hz, and the activation energy Ec/k=409 K.
Rb85, Rb87, and O17 nuclear-quadrupole-resonance study of Rb(H1−xDx)2PO4
(1990-09-01) Seliger, J.; Zagar, V.; Blinc, Robert; Schmidt, V. Hugo
The Rb85, Rb87, and O17 nuclear-quadrupole-resonance frequencies and line shapes have been measured in RbH2PO4 and in Rb(H1−xDx)2PO4 (x=0.5,0.7) with the nuclear-quadrupole double-resonance technique. The results show that in the paraelectric phase the Rb+ ions move in a single-site potential, whereas the protons are dynamically disordered between two sites in the O-H...O hydrogen bonds. The ferroelectric phase transition in RbH2PO4 is associated with the freezing out of the proton motion in the O-H...O hydrogen bonds that induces a shift of the Rb+ ions along the ferroelectric axis. In the partially deuterated compounds the O-H...O hydrogen bonds are practically identical to the ones in pure RbH2PO4 and are thus only weakly influenced by the surrounding O-D...O bonds. The O-D...O bonds are, however, significantly more asymmetric and presumably longer than the O-H...O bonds.
Soft modes and proton tunneling in PbHPO4, squaric acid and KH2PO4, type ferroelectrics
(1984-01) Blinc, Robert; Schmidt, V. Hugo
It 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.