Takanori Fukami

X-Ray Study of Thermal Parameters of NH4H2PO4 and ND4D2PO4 in the Paraelectric Phase

Thermal parameters of P and N atoms of the antiferroelectric NH 4 H 2 PO 4 (ADP) and the deuterated isomorphous ND 4 D 2 PO 4 (DADP) have been observed as a function of temperature in the paraelect...

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.

Studies of ionic conductivity and structural phase transitions of Na3H(SO4)2 crystal

Abstract The complex electrical impedance of Na3H(SO4)2 along the bm-axis has been measured from 25°C to 316°C in the frequency range 4 kHz–40 MHz. The temperature dependence of the electrical conductivity shows remarkable changes in the temperature range 160°C–260°C. The sample crystal becomes a fast ionic conductor above 260°C. The conduction mechanisms of proton and sodium ions in the different phases are analyzed in detail with respect to the structural features of the sample crystal.

Crystal structure and a new phase transition of (ND4)3D(SO4)2 in high temperature phase

Abstract Electric conductivity and X-ray diffraction measurements are performed on deuterated triammonium hydrogen disulphate (ND 4 ) 3 D(SO 4 ) 2 in high temperature phase. A new structural phase transition that corresponds to the transition at 463 K of (NH 4 ) 3 H(SO 4 ) 2 is found at 413 K. The space group symmetry (monoclinic C2) and the crystal structure of (ND 4 ) 3 D(SO 4 ) 2 are determined at 404 K in phase I. The electric conductivity due to the deuterium ion migration in phase I is discussed with respect to the results of the structure refinement.

X-Ray Study of Crystal Structure of ND4D2PO4 in the Antiferroelectric Phase

The crystal structure of 97% deuterated ammonium dihydrogen phosphate (DADP) is analyzed in the antiferroelectric (AFE) phase. Comparing the AFE distortion of PO 4 tetrahedrons and the change of the position of the N atom at the phase transition temperature ( T c ) in DADP with those in ADP, the author found that the distortion and the change of the position are larger in DADP than in ADP. This is consistent with the conclusion obtained by the electron spin resonance (ESR) study. In the AFE phase the AFE distortion of PO 4 tetrahedrons and the position of the N atom do not depend on temperature remarkably. These do not agree with the ESR data.

Structural phase transition and crystal structure of Na3H(SO4)2 in the low temperature phase

Abstract Differential scanning calorimetry and X-ray diffraction measurements are performed on trisodium hydrogen disulphate, Na3H(SO4)2, crystals at low temperatures. A structural phase transition is found at 178(3) K. The space group symmetry (triclinic P1) and the crystal structure are determined at 139K in the new low-temperature phase. It is found that the H atoms on the O─H─O hydrogen bond are not located on the center of the bond. By the shift of the S atom from the center of the SO4 tetrahedron, it points out that Na3H(SO4)2 crystal in the new phase is possible to be ferroelectric with the dipole moment almost along the [1 2 0] direction.

Crystal structures in phases I and II of (ND4)D(SeO4)2 and its phase transitions

Abstract Differential scanning calorimetry, dielectric, electric conductivity and X-ray diffraction measurements were performed on deuterated triammonium hydrogen diselenate (ND4)3D(SeO4)2 crystals. It was found that (ND4)3D(SeO4)2 crystals undergo three phase transitions at 326, 280 and 234K, and that the transition corresponding to the II-III transition at 308K of (NH4)3H(SeO4)2 disappears at around its temperature. The space groups of (ND4)3D(SeO4)2 are trigonal R 3 m in phase I and trigonal R 3 in phase II. The crystal structures in both phases are determined by X-ray diffraction. The electric conduction due to deuterium ion migration is discussed with respect to the results of the observed structures.

Crystal structure and transitions for monoclinic KH2PO4 crystal

A monoclinic form of potassium dihydrogen phosphate, KH 2 PO 4 , crystal has been crystallized. X-ray diffraction and differential scanning calorimetry measurements have been performed on this comp...

Intermediate-range chemical ordering of cations in molten RbCl-AgCl

A first sharp diffraction peak (FSDP) is observed in the X-ray total structure factor of a molten mixture of RbCl-AgCl, while both pure melts of RbCl and AgCl do not exhibit FSDP individually. Molecular dynamics simulations were performed to investigate the origin of the FSDP with the polarizable ion model (PIM). Coexistence of covalent Ag-Cl and ionic Rb-Cl bonds leads the system to evolve intermediate range ordering, which is simulated by introducing the induced polarization in different ways between Ag-Cl with fully polarizable treatment based on Vashishta-Raman potential and Rb-Cl with suppression over-polarization in the nearest neighbor contribution based on Born-Meyer potential. The partial structure factors for both the Ag-Ag and Rb-Rb correlations, SAgAg(Q) and SRbRb(Q), show a positive contribution to the FSDP, while SAgRb(Q) for the Ag-Rb correlation exhibits a negative contribution, indicating that Ag and Rb ions are distributed in an alternating manner within the intermediate-range length scale. The origin of the intermediate-range chemical ordering of cations can be ascribed to the preferred direction of the dipole moments of anions in the PIM.

Crystal Structure and Electrical Conductivity of LiN2H5SO4 at High Temperature.

Electrical conductivity, differential scanning calorimetry and X-ray diffraction measurements have been performed on a single crystal of lithium hydrazinium sulfate, LiN2H5SO4, in the temperature range from 295 K to about 470 K. The crystal structures at several temperatures are determined in this temperature range. The structural phase transition is not found, but an abnormal decrease of the electrical conductivity with increasing temperature above 445 K is observed. The relation between the electric properties and the crystal structures of the sample crystal is discussed. The LiN2H5SO4 crystals are suggested to be proton and Li ionic conductors.