DYNAMICS OF THE NORMAL-DECYLAMMONIUM CHAINS IN THE PEROVSKITE-TYPE LAYER STRUCTURE COMPOUND (C10H21NH3)2CDCL4

The two structural phase transitions in the perovskite layer structure compound (C10H21NH3)2CdCl 4 at Tc1 = 35°C and Tc2 = 39°C have been studied by x-ray diffraction, calorimetric and dielectric measurements, proton NMR spin-lattice relaxation and 'second moment investigations, 35C1 and 14N quadrupole resonance spectroscopy as well as group theoretical considerations. The results show that the transition (T c1) from the low temperature phase (P21/n) to the intermediate temperature phase (Pmnn) is basically a dynamic order-disorder transition of rigid alkyl chains, whereas the transition (Tc2) from the intermediate to the high temperature phase (Amaa) is connected with a melting of the alkyl chains. In the intermediate phase the rigid alkyl chains are flipping around their long axes between two equivalent orientations separated by 90°. The two transitions are somewhat analogous to the ones found in the lipid bilayer membranes and can be described by order parameters used for smectic liquid crystals. © 1979 American Institute of Physics.