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Three inorganic-organic layered perovskite-type hybrids of the general formula (C(n)H(2n+1)NH(3))(2)PbI(4), n = 4, 5 and 6, display a number of reversible first-order phase transitions in the temperature range from 256 to 393 K. (C(4)H(9)NH(3))(2)PbI(4) has a single phase transition, (C(5)H(11)NH(3))(2)PbI(4) has two phase transitions and (C(6)H(13)NH(3))(2)PbI(4) has three phase transitions. In all three cases, the lowest-temperature phase transition is thermochromic and the crystals change colour from yellow in their lowest-temperature phase to orange in their higher-temperature phase for (C(4)H(9)NH(3))(2)PbI(4) and (C(6)H(13)NH(3))(2)PbI(4), and from orange to red for (C(5)H(11)NH(3))(2)PbI(4). The structural details associated with this phase transition have been investigated via single-crystal X-ray diffraction, SC-XRD, for all three compounds.
Billing et al. (Fri,) studied this question.