Origin of giant dielectric constant in Ba[(Fe1−xCox)1/2Nb1/2]O3

The X-ray diffraction Rietveld refinement of Ba[(Fe1−xCox)1/2Nb1/2]O3 with 0 ≤ X ≤ 1 shows cubic structure formation with space group Pm3m. No distinct tilting of oxygen octahedron is observed. The dielectric measurement of such a cubic system exhibited giant values (ɛ′ > 104) in the temperature range of 298–483 K and frequency range of 102–105 Hz. An analysis of the permittivity, electric modulus, and electrical conductivity properties in these systems confirmed the presence of oxygen vacancies induced dipolar relaxation. Our investigations show that the observed extremely high dielectric constant values are predominantly the result of oxygen vacancies induced dipoles produced at the grain boundaries. Additional significant intrinsic contributions to the permittivity comes from the directly doped electrons at the unit cell, as indicated by the enhancement in the observed values of the permittivity on replacement of Fe3+ (3d5) by Co3+ (3d6). The contributions of the doped free charges and the oxygen vacancy induced dipoles are separated using the Jump Relaxation Model.

Research highlights▶ The origin of the high dielectric constant in Ba(Fe1/2Nb1/2)O3 (BFN) with substitution of Co at Fe site by 50% and 100%. ▶ The role of oxygen vacancy and cobalt doping in explaining the induced dielectric relaxation. ▶ The nature of ac conductivity in Ba(Fe1/2Nb1/2)O3 has been explained using the Jump Relaxation Model. ▶ The role of the conduction mechanism of charge carriers is also analyzed using the barrier hopping mechanism.