Symmetry of the normal and low-temperature phase of betaine calciumchloride dihydrate as revealed by 35Cl NMR

Abstract

Quadrupolar perturbed 35Cl NMR spectra are measured in the high-temperature normal (N) phase and in the low-temperature (LT) phase of betaine calciumchloride dihydrate (BCCD) single crystals. The electric field gradient (EFG) tensors at the chlorine sites are precisely determined for both phases. In the N phase, the symmetry of the tensors is in agreement with the space group Pnma known from X-ray studies. The symmetry of the tensors in the LT phase allows to exclude the P11a symmetry proposed previously and confirms the space group Pn2 1a derived theoretically on the assumption that one order parameter drives the phase transitions in BCCD.