INCOMMENSURABLE AND GLASSY BEHAVIOR OF CD2NB2O7 OXIDE PYROCHLORE SINGLE-CRYSTALS

Low-frequency studies of the complex dielectric permittivity of Cd2Nb2 O7 single crystals in the temperature range of 4-80 K are reported. Ab ove T-com similar or equal to 46 K an anomalous thermal hysteresis of epsilon' over the frequency range of 10 kHz-2 MHz as well as dielectri c relaxation may be related to the existence of discommensurations and their dynamics. In the vicinity of T-f similar or equal to 18 K the t emperature and frequency behavior of epsilon is typical of orientatio nal glasses. Two relaxation process fitted with the Vogel-Fulcher law and the Arrhenius law take place near T-f. The first process is relate d to frustration in displacements of the ''seventh'' oxygens relative to Cd2+ ions and is characterized by freezing in of Cd-0(7) orientatio ns below T-0 similar or equal to 7 K. The Arrhenius-type process is re lated to relaxation of ferroelastic and ferroelectric domain walls.