DEUTERON MAGNETIC RESONANCE STUDY OF CUPRIC FORMATE TETRAHYDRATE CU(DCOO)2.4D2O

Deuteron magnetic resonance (DMR) of single crystals of Cu(DCOO)2·4D2O has been studied from 153°K to 291°K to reveal the changes in the structure and the motions of the crystalline water molecules due to the paraelectric-antiferroelectric phase transition (Tc=246.1±0.2°K). Above Tc, all the DMR lines of water molecules are broadened out by fast motions of deuterons among seven sites. Below Tc, 20 pairs of DMR lines are observed corresponding to four water molecules in stable position and two formate ions and their ac -plane enantiomorphs. Following conclusions are derived from measurements of temperature and angular dependences of the quadrupole splittings for these DMR lines. The phase transition is an order-disordering type of water molecules. In the antiferroelectric phase, the unit cell doubling occurs along the c-axis direction and the space group is P21/n. The structure involves a three dimensional ordering of water molecules. The structure of hydrogen-bond network is determined. Each two-dimensional layer of water molecules has a ferroelectric structure and the two successive layers in a unit cell arrange anti-parallel. Torsional motion of formate ion, DCOO-, is activated around the O…O direction. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.