Dielectric properties of Pb(Co_<1/3>Nb_<2/3>)O_3 under pressure

The dielectric properties such as the real ε^' and imaginary ε^" parts of the complex permittivity and the spontaneous polarization Ps of single crystal and ceramic Pb(Co_<l/3> Nb_<2/3>)O_3 with the diffuse phase transition (DPT) were measured under various pressures up to 6 kbar. The value of ε^' shows a broad maximum ε^'_<max> at a temperature T_m (mean Curic temperature). As the pressure increases, the values of ε^'_<max> and T_m decrease, and the shape of ε^' around T_m becomes somewhat sharper. The pressure coefficient of T_m is about -3.5 Kkbar^<-1> for the ceramic and -3.0 Kkbar<-1> for the crystal. Temperature and pressure dependence of ε' and Ps is explained in terms of a phenomenological theory using statistical treatments based on a Gaussian distribution of the local Curie temperature. The value of the standard deviation σ describing the intensity of the DPT is 56 K for the ceramic and 47 K for the crystal, and decreases with increasing pressure