Structural phase transitions of betaine phosphite studied by X-ray scattering

DSC and X-ray scattering studies of betaine phosphite, (CH 3 ) 3 NCH 2 COO·H 3 PO 3 , single crystals have been made. The space group of Phase I (T > 355 K) and that of Phase III (T < 216K) are determined as P12 1 /ml and P12 1 1, respectively, where the cell length of the c axis in Phases II and III are two times larger than that in Phase I. The crystal structure is determined at 373 K. in Phase I and at 173 K in Phase III. The phosphite molecules are disordered in Phase I.