DIELECTRIC-RELAXATION PHENOMENA IN CD2NB2O7 FERROELECTRIC FERROELASTICS

Low-frequency (1 kHz-1 MHz) dielectric permittivity studies of Cd2Nb2O7 single crystals under a uniaxial pressure of 0 MPa less-than-or-equal-to X less than or similar to 4 MPa in a wide measurement AC field strength range of 1 V cm-1 < epsilon < 110 V cm-1 are reported. An analysis of the experimental data reveals that we are concerned with two Debye-type relaxation mechanisms in the ferroelectric phase: T < T(c) (= 196 K) < T(s) (= 205 K). Both of these are manifested when the frequency or the field epsilon is changed, while only the domain relaxation is manifested with increasing pressure. The relaxation caused by domain wall motion and by reorientation of spontaneous polarization of domains dominates. The second relaxation has its origin in the orientation polarizability of the steady Cd2+-O2- (seventh) dipoles in the measurement AC field. The disordered Cd2+-O2- dipole system in the pyrochlore network is formed in the paraelectric phase. Their orientational polarizability in the external electric field results in an anomalously high static dielectric permittivity epsilon0 = 450 compared with epsilon(infinity) = 5.43 at room temperature, as well as dielectric dispersion above T(c) and T(s).