Gd3+ EPR and phase transformations in Cd2Nb2O7

Gd3+ EPR in cadmium pyroniobate in the temperature range 160-300 K has been studied. EPR spectrum in paraelectric phase is described by a spin-hamiltonian of trigonal symmetry. A model of paramagnetic centre is suggested. In the range 197-205 K splitting of EPR lines is observed, which is conditioned by domain formation. Below 197 K additional splitting of EPR lines at THETA=90 deg testifies to the decrease of paramagnetic centre symmetry to triclinic one. The study of the external field effects on EPR permitted to establish the direction of spontaneous polarization [110] in the temperature range T=180-205 K and to detect ferroelectric crystal phase, induced by electric field in the same temperature range. In the temperature range T=197-205 K intensities of EPR lines decrease. The effect depends on sample dimensions and intensity of electric field applied to the sample. Time instability of new lines appearing in the same temperature range is observed