Crystal Structure and Phase Transition of (Glycine)2HNO3 I. Crystal Structure Determination of Ferro- and Paraelectric Phases

The crystal structures of ferroelectric and paraelectric (Glycine) 2 HNO 3 were determined by X-ray as well as by neutron diffraction methods at -150°C and at room temperature, respectively. One of the glycine molecules has the zwitter-ion configuration and another is mono-protonated. Thus the chemical formula should be written as NH 3 + CH 2 COO - ·NH 3 + CH 2 COOH·NO 3 - . Both glycine ions as well as the nitrate ion are nearly planar within the experimental error. A short O-H…O bond, about 2.45A, connects two glycine ions of the different configuration and a proton is attached to the oxygen of the glycinium ion. The paraelectric structure is a disordered one based upon the ferroelectric structure. Such a type of the order-disorder phase transition and the above-mentioned strong hydrogen bond may play an important role for the ferroelectric behaviour of the crystal, which is very similar to the case of (Glycine) 3 H 2 SO 4 .