Dielectric relaxation and electrical conductivity studies in (100 − x)(Li0.12Na0.88)NbO3 − xBaTiO3 (0 ≤ x ≤ 40) ferroelectric ceramics: an impedance spectroscopic analysis

Abstract

Dielectric relaxation and conductivity mechanism in (100 − x)(Li0.12Na0.88)NbO3 − xBaTiO3 (0 ≤ x ≤ 40) ferroelectric ceramics were investigated using impedance spectroscopy over a broad temperature (− 100 °C to 500 °C) and frequency (0.1 Hz to 1 MHz) range. The dielectric relaxation and conductivity mechanism is considered to be associated with oxygen-defect-related complexes (VO··, ((TiNb′ − VO··)·) and ionization of oxygen vacancies (VO··), respectively. The hopping of VO·· in the lattice is considered to be equivalent to a dipolar reorientation contributing to the dielectric relaxation, whereas ionization of VO·· provides some localized electrons (e′) which further contribute to conduction mechanism at higher temperatures. Furthermore, a low-frequency dispersion in dielectric permittivity is observed, which is recognized as a quasi-DC process where the bipolar orientation or the charge carrier transition occurs naturally through discrete movements and that every orientation or transition contributes to e′ makes a proportional contribution to e″. The activation energies of DC conduction (0.64–1.24 eV) and the range of activation energies associated with the grain boundary conduction (0.72–1.22 eV) also indicate that the conduction mechanism is regulated by hopping of electrons through the grain boundary that could be associated to the oxygen vacancies.