GD3+ EPR SPECTROSCOPY AND OPTICAL MICROSCOPY STUDY OF FERROIC STATES IN CD2NB2O7 PYROCHLORE

The EPR spectroscopy (using Gd3+, the EPR probe) and optical microscop y studies of Cd2Nb2O7 pyrochlore were carried out in the temperature r ange of 80 K-300 K which included phase transitions at T-S = 205 K, T- C = 196 K and T-inc = 86 K. The evidence for coexistence of a proper f erroelectric-ferroelastic state and an improper ferroelectric-ferroela stic state in the ferroelectric phase of Cd2Nb2O7 is presented. While the former appears below T-C, the latter comes from the improper ferro elastic state of the precedent phase (T-C < T < T-S). The unusual beha viour of the ferroic states on a temperature scale is discussed from t he viewpoint of a two-weakly-bonded-network description of the pyrochl ore structure.