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Studies on the phase transitions in thiourea

Srinivasan, MR and Rama Rao, AH and Shabanova, LA and Bhat, HL and Narayanan, PS (1978) Studies on the phase transitions in thiourea. In: Ferroelectrics, 21 (1-4). 539-541 .

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Thiourea (CS(NH2)2) is one of the few examples of molecular crystals exhibiting ferroelectric properties. The dielectric constant along the ferroelectric axis [100] shows maxima at 169, 177 and 202 K. An inflection point occurs at 170.5 KZ Following Goldsmith and White the phases are named as I (F.E. below 169 K), II (A.F.E. 169 K<T<176 K), I11 (F.E. 176 K<T<180 K), IV (A.F.E. 180 K<T<202 K) and V (P.E. Above 202 K). The appearance of satellite spots in the x-ray and neutron scattering indicates the presence of structural modulation in phases 11, 111 and IV.4,5 The effect of structural modulation is to destroy the local n glide symmetry, though the overall structure is Pnma. Thiourea also exhibits thermoluminescence after being irradiated with x-rays which is accounted for by defects like NH3+ and NH- formed by the breaking of hydrogen bonds.

Item Type: Journal Article
Publication: Ferroelectrics
Publisher: Taylor and Francis Group
Additional Information: Copyright of this article belongs to Taylor and Francis Group.
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 24 Sep 2010 07:19
Last Modified: 24 Sep 2010 07:19
URI: http://eprints.iisc.ac.in/id/eprint/32433

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