Kazuo Furukawa

Crystal Structure of (NH 4) 3H(SO 4) 2 in Phase I

The crystal structure of triammonium hydrogen disulfate (NH4)3H(SO4)2 in phase I has been studied by single-crystal X-ray diffraction. The space group is assigned as trigonal R\overline3, and the structure parameters are determined. The difference in the structural changes of (NH4)3H(SO4)2 and (NH4)3H(SeO4)2 at the ferroelastic-superionic phase transition is discussed.

Temperature Dependence of EPR Spectrum from VO2+ Ions in (NH4)2SO4

Temperature dependence of EPR spectra from polar VO 2+ probes doped in ferroelectric (NH 4 ) 2 SO 4 crystal was studied in the range between 110 K and 300 K. Impurity ion, VO 2+ , takes substitutionally the position of two NH 4 + ion vacancies so as to satisfy the local charge neutrality. Three kinds of VO 2+ sites in the crystal are identified. One is VO 2+ substituted for II-II pair of NH 4 + ions, another is I-II and the other is I-I. When the temperature is lowered, VO 2+ molecular axes are slightly displaced in a different manner, respectively. From this fact it is concluded that the local electric field is reflected in the VO 2+ displacement. The analyses of the polar angles to the crystal c -axis for VO 2+ in II-II and I-I sites show quite similar profile with anomalous temperature dependence of polarization observed by Unruh. The two-sublattice model for (NH 4 ) 2 SO 4 is supported by the present study.

The Production of Single Crystals of Metals and Alloys with any Desired Orientation by Solidification at High Temperature

In order to grow single crystals of metals and alloys with fairly high melting point in large rods with any desired orientation, a method is developed from the Bridgman method, using a vacuum Tammann furnace and porcelain crucibles with no bottom, sometimes with a perforated sectorial plate, and inserting a seed into the lowest, part of the crucible. We have succeeded in obtaining single crystals of 3.2% and 4.0% silicon steel, and pure nickel, 3 mm diam and 25 cm in length. The rod axes can be fixed in any desired direction. It is noted that the maximum velocity to lower the crucible and its contents, below which a large crystal can grow at each orientation, shows very large anisotropy.

Discontinuous Narrowing of VO2+ Electron Spin Resonance Linewidth in (NH4)3H(SeO4)2 Induced by Superionic Phase Transition

The superionic phase transition in a single-domain crystal of (NH4)3H(SeO4)2 is studied by means of Electron Spin Resonance using VO2+. A discontinuous narrowing of the linewidth is observed at its superionic transition point. This phenomenon can be regarded as a motional narrowing that originates in the dynamic fluctuation of the pyramidal SeO4 tetrahedron which brings about superionic conductivity.