Search

Electrical conductivity, DTA (differential thermal analysis) and NMR measurements have been performed on the KHSO4 crystal. The results of DTA indicates that the KHSO4 crystal shows thermal anomalies at Tc2 = 393 K and Tc1 = 451 K. It is observed that electrical conductivity increases steeply above Tc2. Especially, the motion of proton in each phase was investigated by the NMR measurements. It is also found that the NMR absorption lines above Tc1 become narrow, although the NMR absorption line at 77 K is broad, it is expected that all protons in the crystal move rapidly above T c1. Moreover electrical conductivity is 10-1 S/cm above Tc1. These results indicate that the KHSO4 crystal becomes super-ionic conductor above Tc1. [ABSTRACT FROM AUTHOR]

205Tl-NMR absorption lines in the Tl2SeO4 crystal have been measured below room temperature. We have observed the remarkable changes in the resonance position and line width of the 205Tl-NMR absorption line at TII-III = 97 K and TIII-IV = 74 K. It is also found that the large shift of the resonance position and with decreasing temperature the drastic increase of the line width of the 205Tl-NMR absorption line are observed even in the temperature range from 74 K to 97 K (phase III). Moreover below TII-III we have observed the anomalous 205Tl-NMR absorption lines with two peaks in both tails, although above TII-IIIthe NMR absorption line is described by the single Gaussian curve. In addition, it is found that the positions of two peaks change even in the phase III. These results imply that the Tl2SeO4 crystal shows the structural incommensurate modulation in the phase III, as observed in many A2BX4 type crystals (A = K, Rb, Cs, NH4, N(CH3)4; B=Zn, Co, Se, S; X=Br, Cl, O). [ABSTRACT FROM AUTHOR]

205Tl-NMR absorption lines in the Tl2SeO4 crystal have been measured below room temperature. We have observed the remarkable changes in the resonance position and line width of the 205Tl-NMR absorption line at TII-III = 97 K and TIII-IV = 74 K. It is also found that the large shift of the resonance position and with decreasing temperature the drastic increase of the line width of the 205Tl-NMR absorption line are observed even in the temperature range from 74 K to 97 K (phase III). Moreover below TII-III we have observed the anomalous 205Tl-NMR absorption lines with two peaks in both tails, although above TII-IIIthe NMR absorption line is described by the single Gaussian curve. In addition, it is found that the positions of two peaks change even in the phase III. These results imply that the Tl2SeO4 crystal shows the structural incommensurate modulation in the phase III, as observed in many A2BX4 type crystals (A = K, Rb, Cs, NH4, N(CH3)4; B=Zn, Co, Se, S; X=Br, Cl, O). [ABSTRACT FROM AUTHOR]

Electrical conductivity, DTA (differential thermal analysis) and NMR measurements have been performed on the KHSO4 crystal. The results of DTA indicates that the KHSO4 crystal shows thermal anomalies at Tc2 = 393 K and Tc1 = 451 K. It is observed that electrical conductivity increases steeply above Tc2. Especially, the motion of proton in each phase was investigated by the NMR measurements. It is also found that the NMR absorption lines above Tc1 become narrow, although the NMR absorption line at 77 K is broad, it is expected that all protons in the crystal move rapidly above T c1. Moreover electrical conductivity is 10-1 S/cm above Tc1. These results indicate that the KHSO4 crystal becomes super-ionic conductor above Tc1. [ABSTRACT FROM AUTHOR]

Measurements of 19F and ¹H-NMR absorption lines have been carried out in [(CH2OH)3CNH3]2SiF6 below room temperature. It was found that the 19F-NMR absorption line width becomes narrow with the increase of temperature above around 100 K and becomes almost constant above Tc = 178 K. This result indicates that motional narrowing of 19F-NMR line accompanied by the phase transition at 178 K is observed. It is deduced from this narrowing that the SiF62- anions are reoriented with the correlation time which is fast enough to narrow the 19F-NMR absorption line above Tc. Moreover, we have observed the drastic change of ¹H-NMR absorption line above Tc. This result indicates that the -CH2OH groups begin to reorient by the phase transition at Tc. It is deduced from these results that the motions of SiF62- anions and -CH2OH groups play an important tole in the phase transition at 178 K. [ABSTRACT FROM AUTHOR]

Measurements of 19F and ¹H-NMR absorption lines have been carried out in [(CH2OH)3CNH3]2SiF6 below room temperature. It was found that the 19F-NMR absorption line width becomes narrow with the increase of temperature above around 100 K and becomes almost constant above Tc = 178 K. This result indicates that motional narrowing of 19F-NMR line accompanied by the phase transition at 178 K is observed. It is deduced from this narrowing that the SiF62- anions are reoriented with the correlation time which is fast enough to narrow the 19F-NMR absorption line above Tc. Moreover, we have observed the drastic change of ¹H-NMR absorption line above Tc. This result indicates that the -CH2OH groups begin to reorient by the phase transition at Tc. It is deduced from these results that the motions of SiF62- anions and -CH2OH groups play an important tole in the phase transition at 178 K. [ABSTRACT FROM AUTHOR]

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]