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X-ray study on phase transitions of ferrolectric iron iodine boracite Fe3B7O13I at low temperatures

Kobayashi, Jinzo
Sato, Y.
Published in Physica Status Solidi. A, Applied Research. 1972, vol. 10, p. 259-270
Abstract The accurate lattice parameters of Fe I boracite, Fe3B7O13I, in the low-temp. range between -40 and -120 Deg were successfully detd. by using a special x-ray diffraction technique. To investigate the symmetry change occurring in this temp. range, Weissenberg diagrams were also studied. Ferroelec. Fe3B7O13I exhibits 2 kinds of monoclinic C2s and rhombohedral C36v phases, in addn. to the well-known orthorhombic C52v phase. The 2 kinds of monoclinic modifications, which are stable in the narrow temp. regions between the orthorhombic and rhombohedral phases, appear sep. depending on the history of temp. change of the crystal: one phase arises between -70 and -82 Deg with decreasing temp., the other between -55 and -68 Deg with increasing temp. They have almost similar crystal structures but possess slightly different lattice parameters, thermal expansion coeffs., and optical birefringences. The deviation of the axial angle b from 90 Deg in the monoclinic phases is less than half a minute. The deviation of the rhombohedral axial angle g is also extremely small; the difference from 60 Deg is 48 at -120 Deg. A simple model is proposed to explain the reason why the 2 monoclinic phases must bridge the orthorhombic and rhombohedral phases.
Keywords Phase transition iron iodine boracite
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KOBAYASHI, Jinzo, SATO, Y., SCHMID, Hans. X-ray study on phase transitions of ferrolectric iron iodine boracite Fe3B7O13I at low temperatures. In: Physica Status Solidi. A, Applied Research, 1972, vol. 10, p. 259-270.

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Deposited on : 2013-12-11

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