Toru Ishigaki

Neutron Powder Diffraction Study of Protonic Conductor K3H(SeO4)2

Crystal structures of protonic conductor K 3 H(SeO 4 ) 2 in the phase I (conducting phase) and phase II (room-temperature phase) have been determined using a time-of-flight (TOF) neutron diffractometer VEGA. SeO 4 tetrahedra in the phase I were rotationally displaced with the occupancy 1/3 and the crystal structure in the phase II was remain locally. Proton distribution maps were obtained from the maximum entropy method (MEM) describe that the amount of the proton in a hydrogen bond were decline from 87.3% to 21.4% with increasing the temperature and 13.4% of protons exist at inter-layer space. Incoherent quasi-elastic neutron scattering (QENS) experiments performed by LAM80-ET spectrometer yield the QENS spectra of conducting protons. Proton diffusion constants are estimated as 1.9(1) × 10 − 10 m 2 /s at 393 K and 2.1(3) × 10 − 10 m 2 /s at 413 K, respectively.

Structure Analysis of Propane Hydrates

Clathrate hydrates consist of water cages linked by hydrogen bonds, and various guest molecules. Propane hydrate is contains propane as a guest molecule. The crystal structure is structure II, which is composed of sixteen small cages (S-cage, pentagonal dodecahedron) and eight large cages (L-cage, 16-hedron with 12 pentagonal faces and four hexagonal faces). We synthesized propane deuterohydrate (C3H8 + D2O) and deuterated propane hydrate (C3D8 + D2O). Powder neutron diffraction data were collected on iMATERIA [1] at MLF. Diffraction data were collected from 10 to 150 K. Figure 1 shows the powder neutron diffraction patterns at 10 K. The diffracted peaks of both C3H8 hydrate and C3D8 hydrate were almost the same position. However the peak intensities differed between C3H8 hydrate and C3D8 hydrate. We analyzed by the Rietveld method using Z-Rietveld program [2]. Neutron diffraction patterns revealed that our samples were crystallized as structure II hydrate. We will compare with the previous results [3] and will discuss the difference from our results and temperature dependence of the crystal structure.