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Crystals of tris (methylammonium) nonaiododibismuthate were grown which turned out to be isomorphous with Cs3Bi2I9 and (CH3NH3)3Sb2I9. Two phase transitions, at 223 (second order) and 142 K (first order), were revealed. The low temperature phase transition is characterized by a strong dielectric anomaly. The pyroelectric behaviour could indicate a ferrielectric ordering below 142 K.
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Jakubas et al. (1990) studied this question.
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