Haruhisa Ishigami

Phase transition in K2Fe (SO4)2·2H2O

Abstract The crystal structure of triclinic K2Fe(SO4)2. 2H2O of room temperature was determined by use of an automatic four-circle X-ray diffractomater in space group P1, a=7. 308(1) A, b=10.816(2) A, c=6. 531(1) A, α=109. 03 (1)°, β=110.50(2)°, γ=94. 53(1)°, V=446. 1(2)A3. This Crystal undergoes a phase transition at 364K. The Phase transition is transformed to the same triclinic structure, but the space group is different P1-P .

Dielectric property in K2Fe(SO4)2

Abstract Heat capacity measurements have been made on K2Fe(SO4)2 · 2H2O, from 273 K to 420 K in a differential scanning calorimeter (DSC). Phase transition at 364 K was observed as a sharp peak in the heat capacity curve. The dielectric anomaly was corresponding to DSC observation at 364 K on heating from room temperature. The complex dielectric constant was measured various frequencies in a frequency range between 1 × 106Hz and 1 × 108Hz. The observed temperature and frequency dependence of the complex dielectric constant can be approximated in terms of single relaxation time τ(T) of the Debye type.

Phase Transition in C 8 H 20 XN·2CH 4 N 2 S (X=I, Br, Cl)

The title compounds were prepared by an addition of thiourea to the tetoraethylammonium iodide, bromide and chloride. C 8 H 2 0IN·2CH 4 N 2 S undergoes a phase transition at 288K. The structure at room temperature belongs to orthorhombic system with the space group Ibca ; the low temperature phase is orthorhombic Pccb . Both phase are centric and Z =8. Large differences of the cell dimensions were not found between both phases. The structure consists of the tetraethylammonium cations, iodide anions and thiourea molecules. The main difference between both structures is that the cations show a disordered arrangement at room temperature whereas they are ordered in the low-temperature phase. As the result of structural analysis of tetraethylammonium bromide salt and tetraethylammonium chloride salt, instead of crystallization that two thiourea was added to, it become clear to be crystallization added 4 thiourea and 5 thiourea to.

Mössbauer Effect and X-ray Studies of the Phase Transitions in K 2 Fe(SO 4 ) 2 ·nH 2 O(n=2,4,6)

A detailed study of Mössbauer spectra for K 2 Fe(SO 4 ) 2 ·nH 2 O(n=2,4,6) has been performed. Isomer shift and quadrupole splitting of 57 Fe were measured as functions of temperature between 90 K and 370 K. Single crystals of dipotassium iron sulfate, K 2 Fe(SO 4 ) 2 ·nH 2 O were grown by slow evaporation of aqueous solutions of K 2 SO 4 and FeSO 4 in equimolar ratio. Since it was necessary to keep the solution above 360 K to obtain dihydrate crystals, K 2 Fe(SO 4 ) 2 ·2H 2 O was grown at 369 K. The crystal is known to undergo a phase transition which is associated with the water molecular orientation. The Mössbauer study was also performed on the crystals K 2 Fe(SO 4 ) 2 ·4H 2 O and K 2 Fe(SO 4 ) 2 ·6H 2 O for the search of the possible phase transitions similar to that of K 2 Fe(SO 4 ) 2 ·2H 2 O. The part of the X-ray structure analysis for these crystals is also given.

Phase transition in C8H20IN. 2CH4N2S

Abstract The crystal of the title compound undergoes a phase transition at 288K. Structure determinations were made at 296K and 153K. The structure at room temperature belongs to orthorhombic system with the space group Ibca; the low temperature phase is orthorhombic Pccb. Both phase are centric and Z=8. Large differences of the cell dimensions were not found between both phases. The structure consists of the tetraethylammonium cations, iodide anions and thiourea molecules. No short contacts other than van der Waals ones are observed. The main difference between both structures is that the cations show a disordered arrangement at room temperature whereas they are ordered in the low-temperature phase. The disordered cation statistically occupies two sites relating the two-fold rotation axis with one-half occupancies each.

Mössbauer study of the phase transitions in some iron sulfate and iron chloride compounds

Abstract Quadrupole coupling with electric field gradient is a sensitive indicator for structural phase transitions. 57Fe Mössbauer spectroscopy provides us with quadrupole couplings of 57Fe nuclei with surrounding electric field gradients(EFG). We report here about the Mössbauer spectroscopy of K2Fe(SO4)2•L2H2O, FeCl2•L6H2O and [N(CH3)4]2FeCl4. The crystal K2Fe(SO4)2•L2H2O was recently found to undergo a ferroelectric phase transition at 364 K. The Mössbauer spectrum of this crystal shows only one doublet both in the paraelectric and ferroelectric phases. The quadrupole splitting shows quite similar temperature dependence to that of order parameter. The deuterated crystal was also investigated by Mössbauer spectroscopy. The crystal FeCl2•L6D2O was reported to undergo a phase transition at around 126K. We have measured Mössbauer splittings in FeCl2•L6H2O down to 12 K. A doublet line is observed at room temperature down to 22K. We have also studied the crystal [N(CH3)4]2FeCl4 which shows pressure-induced ferroelectricity and incommensurate phase transition.

Mössbauer spectroscopy of some iron compound ferroelectrics

Abstract Iron environment was investigated by 57Fe Mossbauer spectroscopy on the crystals [N(CH3)4]2FeCl4 and K2Fe(SO4)2•2O. The former crystal undergoes successive phase transitions including an incommensurate phase. Single doublet was observed in the orthorhombic phase (Phase I). The spectrum is almost the same in the incommensurate phase (Phase II) and in the Phase II’where the structure is modulated in the z-direction with the wavenumber 3/7. These modulation seems to raise no large EFG modulation to cause noticeable change in the spectrum. A new doublet appears in the Phase III where the structure is commensurate with the cell tripling along the c axis. This doublet persists even to the Phase IV where the structure is monoclinic with Z = 4. If we consider the crystal symmetry, the extra doublet is prohibited in this phase. The extra EFG is interpreted as the peculiarity to the powder sample. The spectrum of K2Fe(SO4)2•2H2O shows only one EFG and its temperature dependence is quite similar to the orde...