REDETERMINATION OF THE CRYSTAL-STRUCTURE OF PARAELECTRIC DIGLYCINE NITRATE .2. SHORT-RANGE ORDER AT 220 K AND 293 K

Precise determination of the crystal structure of diglycine nitrate (N H2COOII)(2)NO3 (DGN) at 220 K and 293 K, confirmed that at both temper atures paraelectric DGN consists of distributed at random polar lattic e cells of opposite polarity. The application of our new method which we call refinement of the g-parameter proved that in the crystal struc ture of paraelectric DGN there is a short range order and the structur e consists of small clusters of opposite polarity. The clusters grown in size on approaching the ferroelectric phase transition. This model explains the temperature dependence of occupancy factors of disordered nitrate anions which adjust themselves depending on the polarity of n eighbouring glycine molecules. Lattice parameters of DGN determined by the Bond method as a function of temperature in the range 160-295 K, confirm the second order of the ferroelectric phase transition of DGN.