1962 Volume 35 Issue 7 Pages 1199-1205
The dielectric properties of single crystals of cupric formate tetrahydrate have been investigated over the range 30c./sec. to 10 Mc./sec. from the liquid nitrogen temperature to the dehydration point, 46°C. This crystal undergoes a phase transition at –36°C, indicated by a sudden change in the dielectric properties. Above the transition point, large dielectric dispersion and absorptions are present when the applied electric field is along the crystallographic a- and b-axes, whereas along the normal to (0 0 1) plane, the variations in permittivity and the loss factor with temperature and frequency are quite small.
The results for the radio frequency absorption can be explained on the basis of a molecular mechanism involving the axial reorientation of two water dipoles in the formula unit of Cu(HCO2)2·4H2O. The energy barrier H(kcal./mol.) and the frequency factor A(sec−1) associated with the dipole orientation have been obtained as follows : along the a-axis A=1×1011, H=6.7; along the b-axis A=8×109, H=4.5; and in the direction normal to (0 0 1) A=7×1010, H=6.3.
A further absorption at much lower frequencies is remarkable only in the a-axis direction. The observed high dielectric loss suggests the possibility of proton transfer in the hydrogen-bonded chains found in this crystal structure.
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