DIELECTRIC-RELAXATION PHENOMENA IN CD2NB2O7 FERROELECTRIC FERROELASTICS

Low-frequency (1 kHz-1 MHz) dielectric permittivity studies of Cd2Nb2O 7 single crystals under a uniaxial pressure of 0 MPa less-than-or-equa l-to X less than or similar to 4 MPa in a wide measurement AC field st rength range of 1 V cm-1 < epsilon < 110 V cm-1 are reported. An analy sis of the experimental data reveals that we are concerned with two De bye-type relaxation mechanisms in the ferroelectric phase: T < T(c) (= 196 K) < T(s) (= 205 K). Both of these are manifested when the freque ncy or the field epsilon is changed, while only the domain relaxation is manifested with increasing pressure. The relaxation caused by domai n wall motion and by reorientation of spontaneous polarization of doma ins dominates. The second relaxation has its origin in the orientation polarizability of the steady Cd2+-O2- (seventh) dipoles in the measur ement AC field. The disordered Cd2+-O2- dipole system in the pyrochlor e network is formed in the paraelectric phase. Their orientational pol arizability in the external electric field results in an anomalously h igh static dielectric permittivity epsilon0 = 450 compared with epsilo n(infinity) = 5.43 at room temperature, as well as dielectric dispersi on above T(c) and T(s).