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Phase transition in K2Fe(SO4)2·2H2OHaruhisa Ishigami a , Minoru Sumita a & ShoichiSato ba Laboratory of Natural Science, Faculty ofEngineering, Shibaura Institute of Technology,Ohmiya, Saitama, 330, Japanb X-ray Research Laboratory, Rigaku Corporation,Akisima, Tokyo, 196, JapanVersion of record first published: 09 Mar 2011.

To cite this article: Haruhisa Ishigami , Minoru Sumita & Shoichi Sato (1999):Phase transition in K2Fe (SO4)2·2H2O, Ferroelectrics, 229:1, 109-114

To link to this article: http://dx.doi.org/10.1080/00150199908224326

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Ferroelecfrics, 1999, Val 229, pp. 109-114 Reprints available directly from the publisher Photocopying permitted by license only

0 1999 OPA (Overseas Publkhers Association) N.V. Published by license under the

Gordon and Breach Science Publishers imprint. Printed in Malaysia

Phase Transition in K2Fe (S04)2*2H20

HARUHISA ISHIGAMIa. MINORU SUMITAa and SHOICHI S ATOb

aLaboratory of Natural Science, Faculty of En ineering, Shibaura Institute of Technology, Ohmiya, Saitama 330, Japan and % X-ray Research Laboratory,

Rigaku Corporation, Akisima, Tokyo 196, Japan

(Received December 8, 1998)

The crystal structure of triclinic K,Fe(S04), 2H20 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, c~=109.03 (1)" , p=110.50(2)", p94.53(1)" , V=446.1(2) A3. This Crystal undergoes a phase transition at 364 K. The Phase transition is transformed to the same triclinic structure, but the space group is different Pl-Pi

Keywords: phase transition; X-ray diffraction; space group; K2Fe(S04), 2H20

1. INTRODUCTION

I t is well known that potassium iron sulfate, KzF~(SOI)Z. 2H20, crystallized stably in the triclinic system"' at room temperature. But very little published informations available about this crystal. Heat capacity measurement have been made on KrFe(SO4)z. 2H20, from 273K to 420K in a differential scanning calori-mater@SC). A 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

109

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110 HARUHISA ISHIGAMI et al.

room temperature'". Very recently we have determined the crystal structure of KZe(S0)2*2H20 at 297 K and 373 K. The present paper report the details of the crystal structure and phase transition of the triclinic KrFe( S04)z - 2H20.

2. EXPERIMENTAL

Single crystal of KZFe(SOb.2H20 was grown by slow evaporation from an aqueous solution of KzSOI and FeSOA in equimolar ratio. A colorless prismatic crystal of KZe(S0,)2 * 2H2O having approximate dimension of 0.40~0.35~0.50 mm' was mounted on a glass fiber. All measurements were made on Rigaku AFC5R diffractometer with graphite monochromated Mo Ka up to 2&70 ' . In total 41 15 reflection were collected. Of these, 3909 were used for structure determination. Cell constant and an orientation matrix for data collection, obtained from a least-squares refinement using the scatting angle of 25 carehlly centered reflections in the range 39.30<2&39.98 corresponded primitive triclinic cell with dimensions; a=7.301(l)a, b=10.816(2)a, c=6.553(1)a, a=109.03(1)' , ~=110.50(2)" , y=94.53(1)" , V=446.1(2)a '. For 2=2, FW=362.19, the calculated density is 2.70gkm'. Based on a statistics analysis of intensity distribution, and the successful solution and refinement of the structure, the space group was determined to be PI. Next, intensities of high temperature phase was measured on a AFC7R at 373K. Experimental conditions were similar those at room temperature. The cell dimensions are : 0=7.296(2) a , b=5.377(2) a , d .567(2 ) a , a=107.99(2)' , ~110 .13(2 ) ' , y=94.59(2)" , V=446.1(2)a ', Z=1. The space group was Pi.

3. STRUCTURE DETERMINATION

The structure was solved by patterson method. Hydrogen atom were deduced From D-syntheses and refined isotropically (the hydrogen atoms in the high temperature structure were not refined). The structure successfully converged: R-0.025, Rw =0.045 and S=1.94 for the room temperature phase, and M.034 , Rw=0.069 and S2 .21 for the high temperature phase.

4. RESULT AND DISCUSSION

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PHASE TRANSITION IN K2Fe(S04)2.2H20 111

The atomic coordinates and Bq's are listed in table 1.

TABLE 1 The atomic coordinates and Bq's. (a) at 297K and (b) at 373K

lrtMn Fe 1 Fe2 K1 K2 K3 K4 s1 s2 s3 s4 01 02 03 04 05

.06 a7 08 09 010 01 1 012 013 014 015 016 017 018 019 020 H1 H2 H3

H5 H6 H7 ti8

n4

atom Fe 1 K1 SI 01 02 03 04 05 HI H2

X 0.520 0.47726 (6) 0. 2 4 1 (2) 0. 7608 (2) 0. 7476(2) 0.2359(2) 0. 7205 (2) 0.2723(2) 0.2748 (2) 0. 7245(2) 0.5689(6) 0.8501 (6) 0.8398 (6)

0.4074(6) 0. 1696(6) 0. 1325(6) 0.3983 (6) 0.2243 (6) 0.8030 (6) 0.4268 (6) 0. 15546) 0. 1506(7) 0; 3859 (6)

0.8357(6) 0.8634 (7) 0.5992 (7) 0.77846) 0. 1907(6)

0.173

0.837 0.824 0. 172

0.613a(6)

0.5we (6)

0.168

0. 826 0. a89

0.085

x 0. 500 0.24321 (6) 0. 72303 (5) 0.5862(2) 0.8557(3) 0.8342 (2) 0.5985 (2)

0.134 0.173

0.2048

(a)

0.75080(3) 0. lool(1) 0.4208(1) 0.8979(1) 0.57750) O.O74O(I) 0.41ei(i) 0.9239 (1 ) 0.5804(1)

-0.0477(3) 0.1215(3) 0.0409 (3) 0.1802 (3) 0.3277 (4) 0.4209 (3)

0.2W9 (4) 0.2665 (4) 1.0460 (4) 0.8754(4) 0.9519 (4) 0.8191(4) 0.6787 (3) 0.5636 (4) 0.6338 (4) 0.4506 (3) 0.76#0(4) 0.7285 (4) 0.157 0. 284 0.215 0. 280 0.847 0. 716 0.784 0. 719

c. 250

8: E 14

(b) Y 0.500 0. 19502(9) 0. 14916(6)

-0.1038(2) 0.2450 (3) 0. 1061 (3) 0.3505 (2) 0.4610(3) 0.286 0.579

I 0.300 0.50019 (6) 0. em (2) 0.1832 (2) 0.1874 (2) 0.8101 (2) 0.8W6 (2) O.leda(2) 0.1727 (2) 0.8096 (2) 0.7579 (7) 1.0726 (5) 0.6795 (7 0.7743(6! 0. 2223(6) 0.3399(7) 4.0608 (7) 0.2413(6) 0.4889 (6) 0.4828 (6) 0.2364 (7)

4.0863 (6) 0.3081 (7) O.ZlrO(6) 0.7736 (6) 0.6473(6) 1.0567 (5) 0.7534(6) 0.5034(7) 0.5073 (7) 0.375 0.410 0.373 0.579 0.610 0.563 0.625 0.395

I 0.560

0.81236 (5) 0.7572 (2) 1.0577(2 0.6592 (31 0,7731 (2) 0.4961 (2) 0.372 0.441

0. ezoos(7)

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112 HARUHISA ISHIGAMI et al

U

FIGURE 1 Paclung diagrams. (a) at 297K and (b) a! 373K.

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PHASE TRANSITION IN K,Fe(SO4),.2H2O 113

The structure consist of SO1 tetrahedra, Fe06 octahedra and KCb irregular polyhedra. Four SO4 ions and two water molecular axially coordinate to an Fe atom to form Fe06 octahedron. Neighbour octohedra are bridged by two SO+ tetrahedra with cornersharing to form linear chains along the b axis. The chain linked by K atoms and hydrogen bonds form layers parallel to the ( 100) plane. The crystal easily cleaves along the ( 100) plane. The bonding across the cleavage plane generally weak; in the present crystal, this is quite reasonable fiom the characteristics of the two-dimensional layered structure. Fig.2. shows projections of both structures along the a axes.

FIGURE 2 octohedra and so4 tetrahedra (a) at 297K and (b) at 373K. Paired small circles are water hydrogen atoms, circles on the tetrahedra is K atoms.

Projections of the structures indicated by FeO6

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114 HARUHISA ISHIGAMI et al.

Above the T,, the structure becomes center symmetric not only the molecular units become equivalent but also the Fe atom itself occupies an inversion center; thus the cell axis is halved along the b axis. A distinct change is the rotation of one of the water molecules. This rotational change might result in both changes of the hydrogen bond formation and slight atoms displacement.

References [l] Gmelins Handbuch der Anorganischen Chemie, 59,927, (1932). [2] H. Ishigami and M. Sumita, (1997). Presented at the annual meeting of the Physical

Society of Japan held in Kobe, Oct. 5-8(7aF12).

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