Tsutomu Okuda

Chloride ion conductor CH3NH3GeCl3 studied by Rietveld analysis of X-ray diffraction and 35Cl NMR

Abstract The chloride ion conductor CH3NH3GeCl3 was characterized by DTA, Rietveld analysis of the powder X-ray diffraction, and 35Cl NMR. The mobile ion at the high temperature phase was deduced to be a chloride ion, because a disordered perovskite structure at the Cl site was found by the Rietveld analysis. This disordered model was also confirmed by 35Cl NMR. The mechanism of the ionic conductivity and the process to attain a conducting phase were discussed on the basis of the temperature dependence of the powder X-ray diffraction and the spin-lattice relaxation times of 35Cl NMR.

Zeeman effect on the nqr of the complex of copper(I) halide with triphenylphosphine

Abstract Nuclear quadrupole resonance (NQR) frequencies due to 63Cu were observed for Cu2X2(PPh3)3 (X=Cl, Br, and I). Each compound has two NQR lines in the separated frequency regions, 13-16 MHz and 27-30 MHz. The Zeeman effect on the higher lines was examined by using single crystals in order to deduce the asymmetry parameters of the electric field gradient tensor, which were found Co be 0.29, 0.31, and 0.33 for X=Cl, Br, and I, respectively. In the case of Cu2Br2(PPh3)3, two 81Br NQR lines were found at 47.52 and 49.53 MHz with large asymmetry parameters of 0.997 and 0.987, respectively.

Fluoride ion diffusion of superionic PbSnF4 studied by nuclear magnetic resonance and impedance spectroscopy

Superionic material PbSnF4 prepared by precipitation from aqueous solution was characterized by x-ray diffraction, DTA and 19 F nuclear magnetic resonance (NMR) techniques. The temperature and frequency dependence of the conductivity, the modulus and the dielectric properties were investigated by means of impedance spectroscopy. The Arrhenius plot of the dc conductivity shows a gradual slope change around 355 K from a high-activation-energy (Eσ = 30 kJ mol−1) region to a low-activation-energy region (Eσ = 22 kJ mol−1). At lower temperatures the real part of the ac conductivity exhibited a power-law behaviour as found in most ionic conductors. At high temperatures, on the other hand, a low-frequency dispersion of the conductivity was observed due to the space charge polarization, which resulted from the high ionic conductivity. An extremely large dielectric constant was observed with decreasing frequency due to the space charge polarization. A dielectric anomaly was also observed around the phase transition temperature. The modulus formalism was used to estimate the conductivity relaxation times and was compared with those from the line width transition of the 19 F NMR.

Structural analysis of lithium-excess lithium manganate cathode materials by 7Li magic-angle spinning nuclear magnetic resonance spectroscopy

Abstract The local structures of lithium-excess lithium manganese spinel oxides were studied by high-resolution solid-state 7 Li magic-angle spinning (MAS) NMR spectroscopy. Two resonance lines at ∼500 and ∼555 ppm were observed for the spinels in 7 Li MAS NMR spectra. Spinel stability tests in which spinel powder was stored in electrolyte solution were performed to analyze the changes in the lithium local structure after manganese dissolution. After the spinel stability test, the intensity of the resonance at ∼500 ppm decreased, whereas new resonance line at 0 ppm was observed. The lithium content of the 0 ppm peak increases with the storage time in electrolyte. SEM and chemical analysis suggested a surface coating of non-spinel lithium compounds, the presence of defects on particles surface and fluorine incorporation into the aged spinel. In addition, about 60–70% of lithium remains in the spinel framework after the storage.

NQR and X-ray Studies of [N(CH3)4]3M2X9 and (CH3NH3)3M2X9 (M = Sb,Bi; X = Cl,Br)

Abstract 35Cl, 81Br, 121Sb, and 209Bi NQR of the title compounds was observed. According to the results of the temperature dependences of NQR frequencies and the DTA measurements, phase transitions take place in [N(CH3)4]3Bi2Br9 (Ttr=183K), [N(CH3)4]3Bi2Cl9 (Ttr = 155K), and (CH3NH3)3Bi2Cl3 (Ttr = 200 and 249 K). 2D NMR spectra for partially deuterated (CH3ND3)3Bi,Br9 showed that the phase transitions in this compound are related to the motion of the methylammonium cations. Single-crystal X-ray work at room temperature shows that the space group for [N(CH3)4]3Sb2Cl9 is P63/mmc with a = 925.1 pm, c = 2173.4 pm, Z = 2. For (CH3NH3 ) 3Sb2Br9 the space group is P3ml with a = 818.8 pm, c = 992.7 pm, Z = 1; in both cases the cations show dynamical disorder. The Rietveld analysis of the powder X-ray diffraction for (CH3NH3)3Bi2Br9 reveals the space group P3ml with a = 821.0, c - 1000.4 pm, Z = 1 at room temperature; the compound is isomorphous with (CH3NH3 )3Sb2Br9 . The crystal symmetries of the low-temperature phases of (CH3NH3)3Bi2Br9 and [N(CH3)4]3Bi2Br9 were deduced from the results of the NQR spectroscopy

Fluoride ion dynamics and relaxation in KSn2F5 studied by 19F nuclear magnetic resonance and impedance spectroscopy

Ion dynamics in the two-dimensional fluoride ion conductor KSn2F5 have been studied by 19F nuclear magnetic resonance (NMR) and impedance spectroscopy. The electrical relaxation behaviour of the investigated material is represented in the conductivity and electric modulus formalisms. The values of the dc conductivity and the hopping frequency of mobile ions and their respective activation energies are estimated from the analysis of the conductivity spectra using Almond–West formalism. The activation energies for conduction and ion hopping processes are almost identical, with values of 0.53 and 0.54 eV, respectively, suggesting that the concentration of charge carriers is independent of temperature. The Roling scaling approach to the conductivity spectra is applied in order to gain insight into the temperature dependence of the relaxation mechanism. The scaling law successfully collapses the conductivity spectra into a single curve, indicating a temperature-independent relaxation mechanism. Moreover, chemical exchange simulation of the 19F NMR spectra is introduced. The discrepancy between the values of the activation energies deduced from the electrical and NMR experiments are discussed according to Ngais coupling model.

The structural investigation of SbBr3· (POBr3)2 BY 81Br and 121SbNQR

Abstract 81 Br and 121 Sb NQR have been observed for SbBr 3 ·(POBr 3 ) 2 , and the Zeeman effect on 81 Br NQR lines examined at 77 K. It is considered from these results that this complex consists of a dimer of two SbBr 3 ·(POBr 3 ) 2 molecules bridged by two Br atoms.

Application of the Mössbauer spectroscopy to the study of the oxidation state of azaferrocene derivatives

Azaferrocene has two active sites of iron and nitrogen atoms. Drastic change of the oxidation state in iodine oxidation of azaferrocene is observed by introducing the methyl substituents into the pyrrole ring, while all the N-methylates show a similar electronic state. It was revealed that an introduction of methyl substituent to the pyrrole ring promotes the oxidation of nitrogen atom in pyrrole ring more than the central iron atom.

Successive Phase Transitions and High Ionic Conductivity of Trichlorogermanate (II) Salts as Studied by 35C1 NQR and Powder X-Ray Diffraction

Abstract A series of trichlorogermanate(II) salts (AGeCl3, A = Rb, Cs, CH3N H3, and (CH3)4N) have been synthesized and characterized by 35Cl NQR , 35Cl NMR , AC conductivity, DTA, and X-ray diffraction techniques. In the temperature range studied two, two, five, and four phases were confirmed for the Rb, Cs, CH3NH3, and (CH3)4N salts, respectively. From the 35Cl NQR and structural data, isolated pyramidal GeCl3 anions were recognized in the low temperature phases. With increasing temperature the relaxation times of the 35Cl NQR decreased exponentially and the signals disappeared far below the melting point. This suggests that the reorientation of the anion about the pseudo three-fold axis is excited. With further increase in temperature, the ionic conductivity of CH3NH3GeCl3 and (CH3)4NGeCl3 increased drastically at the phase transitions to their cubic perovskite phases (CH3NH3GeCl3:σ= 10-1 Sm-1 at 400 K, (CH3)4NGeCl3: σ = 5 x 10-2 Sm-1 at 420 K). The mobile ion was confirmed to be the chloride ion by means of 35Cl NMR and X-ray diffraction.

127I-NQR, 119 Sn Mössbauer Effect, and Electrical Conductivity of MSnI3 (M = K, NH4 , Rb, Cs, and CH3NH3 )

Abstract In a series of MSnI3 compounds (M = K, NH4 , Rb, Cs, CH3NH3) two types of coordination around the central Sn(II) were found by 127I-NQR and powder X-ray diffraction techniques. They are square pyramidal (for M = NH4 , Rb) and octahedral (for M = CH3NH3). CsSnI3 , on the other hand, showed a drastic structural change of the anion at 425 K from a square pyramid to a regular octahedron. Associated with this phase transition, the electrical conductivity increased from 4 x 10-3 S cm-1 to about 102 S cm-1 . This metallic modification was characterized by 127I-NQR and 119Sn Mössbauer spectroscopy.