Order-disorder of TMA ions and phase transitions in tetramethylammonium calcium chloride (TMCC) studied by NMR

N-14 NMR measurements enable to study the ordering of tetramethylammonium (TMA) ions in relation to the phase transition from the high-temperature hexogonal phase (space group P6(3)/M, Z = 2 formula units) to a ferroelastic phase (P2(1)/m) of TMCC. The results are discussed on the base of theoretical predictions about the orientational order of the TMA groups in the well-known contribution of Braud et al. for crystals of the isostructural family of TMA haloid compounds.