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Abstract: We have carried out the electrical conductivity and NMR measurements and investigated the characteristic features of the electrical conductivity in a paraelastic phase of Tl2SeO4. It was found from electrical conductivity measurement that the activation energy in the paraelastic phase (above T c(=661 K)) is 0.98 eV. We also found that 205Tl-NMR line width drastically decreases above T c and becomes approximately 0.5 Gauss. This result indicates that in the paraelastic phase the mobile Tl ions exist. Moreover this result is consistent with the existence of the anomalously large hopping motion of Tl ions observed in X-ray diffraction measurement. Furthermore the activation energy estimated from the motional narrowing of 205Tl-NMR absorption line is 0.92 eV and is in agreement with that obtained from the conductivity measurement. From these results, it is deduced that the mobile Tl ions play an important role in the appearance of electrical conductivity in the paraelastic phase. [Copyright &y& Elsevier]

Abstract: We have carried out the 1H-NMR and X-ray measurements, in order to reveal the origin of the relatively high electrical conductivity observed even below a superprotonic phase transition at T c (=449 K) in Rb3H(SeO4)2. It is found that the second moment of the 1H-NMR absorption line rapidly decreases around 338 K with increasing temperature. This result indicates that the hopping motion of a proton, which is the precursor motion of proton motion in the superprotonic phase, appears around 338 K. This result indicates that the increase in the proton mobility above 338 K is closely related with the increase of slope in the temperature dependence of the electrical conductivity around 338 K with increasing temperature. Furthermore a spontaneous strain obtained from the X-ray diffraction data steeply decreases around 338 K. From these results, it is deduced that the increase in the proton mobility above 338 K is caused by the same mechanism as the decrease in the spontaneous strain and yields the proton conductivity observed even below T c. [Copyright &y& Elsevier]

Abstract: Electrical properties and 1H-NMR absorption line have been measured, in order to investigate proton dynamics in a superionic phase in Tl3H(SO4)2. From the measurement of the thermoelectric power, it is found that a majority carrier in electrical conductivity is a proton. Moreover, from 1H-NMR measurement it is also found that the activation energy 0.33eV of the hopping motion of protons is close to 0.38eV as observed in the electrical conductivity measurement. These results indicate that the electrical conductivity in the superionic phase is caused by the hopping motion of protons accompanied by the breaking of the hydrogen bonds. [Copyright &y& Elsevier]

Proton dynamics of the TlHSO 4 crystal was investigated by 1 H-NMR spectroscopy. The NMR absorption line at 77 K is described well by two broad absorption lines known as the Pake doublet. From this result, the distance between the nearest neighbor protons is calculated to be 3.0 Å. Moreover, the sharp absorption line is observed even below a superionic phase transition temperature T II-III (388 K). This result indicates that the mobile protons exist even below T II-III . Furthermore, it was found from the analyses of these NMR absorption lines that the ratio of the number of the mobile proton to all proton increases drastically above T III-IV = 320 K and becomes 100% even at about 20 K below T II-III . [ABSTRACT FROM AUTHOR]

It was found from the temperature dependence of spin-lattice relaxation rates of 1 H and 205 Tl nuclei ( 1 H- T 1 -1 and 205 Tl- T 1 -1 ) that spin-lattice relaxations of 1 H and 205 Tl result from a magnetic dipole-dipole relaxation. It was also found from the analysis of T 1 's that the energy for the flip-flop motion of protons from O…H--O to O--H…O becomes 2.0 meV at low temperatures. These results suggest that Tl 3 H(SO 4 ) 2 shows the quantum mechanical process such as proton tunneling at low temperatures. The anomalous behavior of 1 H- T 1 -1 at around 61 K indicates that proton dynamics is changed at around 61 K. Furthermore, it is suggested from the anomalies of 1 H- T 1 -1 and 205 Tl- T 1 -1 at around 7 K that Tl 3 H(SO 4 ) 2 shows a phase transition accompanied by the anomaly of the magnetic dipole-dipole fluctuation at around 7 K. [ABSTRACT FROM AUTHOR]

We have studied the proton dynamics on Tl 3 H(SO 4 ) 2 from the measurements of 1 H-NMR absorption lines. It was found that the NMR line width Δ H at room temperature becomes about 20 times narrower than that at 77 K and that the NMR absorption line at room temperature shows the mixture functional form of the Gaussian and Lorentzian. These results indicate that protons migrate even at room temperature: that is, Tl 3 H(SO 4 ) 2 becomes a super-ionic conductor at room temperature. From the temperature dependence of Δ H , we have obtained the result that the phase transition at T II-III = 239 K corresponds to the super-ionic phase transition. Furthermore, we calculate the proton correlation times from the line widths and determine the activation energy of proton motion in the phase II (super-ionic phase) to be 0.33 eV. This result indicates that proton migration lead to the electric conductivity in the super-ionic phase. [ABSTRACT FROM AUTHOR]

Proton NMR line width and spin-lattice relaxation time T 1 for the ferroelectric (CH 3 ) 2 NH 2 H 2 AsO 4 have been measured at the temperature range between 77 K and 300 K. The temperature dependence of T 1 is well described by the expressions based on rotation of the methyl group using the value of activation energy E a = 99 meV and elementary correlation time τ 0 = 1.5 × 10 -13 sec. Moreover, a sharp dip of T 1 near ferrroelectric phase transition temperature ( T c = 274.5 K) results from the ordering of protons. In addition, the temperature dependence of T 1 deviates from the expression for molecular rotation above around 200 K. It is deduced that the deviation is caused by the suppression of some kind of proton motion. [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate the proton dynamics and the mechanism of the relatively high-electrical conductivity observed even below T c in Rb3H(SeO4)2, we have measured the 1H spin-lattice relaxation rate. From the measurement of the 1H spin-lattice relaxation rate T 1 −1, it is found that the temperature dependence of T 1 −1 takes a peak at around 345 K. The analysis of the temperature dependence of T 1 −1 shows that T 1 −1 in Rb3H(SeO4)2 is described well by the dipole–dipole relaxation between proton and Rb nuclei. Moreover, it was also found that not only the proton dynamics described by a hopping motion of proton between two equivalent sites in the hydrogen bond but also a new process of proton transfer appears above around 338 K. This new process is a hopping motion of proton accompanied by the breaking and rearrangement of hydrogen bond. From these results it is deduced that the increase of the electrical conductivity observed even below T c is caused by the proton transfer between possible stable sites accompanied by the breaking and rearrangement of hydrogen bond, and that electrical conductivity in Rb3H(SeO4)2 is dominated by protons motion even below T c. [Copyright &y& Elsevier]