Structural anomaly and electrical relaxation in (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics

The X-ray diffraction patterns of (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics were measured within 15–850 K temperature range. The anomaly in the thermal expansion temperature dependence occurred in 250–365 K range. The generalised Cole–Cole model was proposed to describe the measured effective electric permittivity influenced by high electric conduction and the coexistence of two contributions ɛ*(T,f) = ɛ*lattice + ɛ*carriers was considered. The analysis of the electric permittivity and conduction exhibited two relaxation processes. The electric conduction relaxation characteristic time values indicated the small polaron mechanism with τ0 ≈ 10−13 s occurring in 240–345 K range and the ionic mechanism with τ0 ≈ 10−11 s involved in the other relaxation occurring in the 320–510 K range. The ionic relaxation process was ascribed to a subsystem of defects, which was weakly interrelated to the anomaly in thermal expansion of the (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics. The Gate model was proposed to describe the ionic relaxation mechanism.