  Dielectric behavior and conductivity mechanism in lead-free
(100-x)(Li0.12Na0.88)NbO3-xBaTiO3 (0 to x to 40) piezoelectric ceramics were
investigated using impedance spectroscopy over a wide temperature (-100 oC
to500 oC) and frequency range (0.1 Hz to1 MHz). The grain and grain boundary
response as well as the relaxation processes at different frequencies and
temperatures were also discussed. A low frequency dispersion in dielectric
permittivity (LFDD), a typical characteristic of high-temperature behavior was
observed both below and above the ferro-paraelectric phase transition
temperature, Tm. Oxygen-defect-related complexes generated due to acceptor type
doping were found to play an important role in LFDD and hopping conduction. The
dielectric relaxation follows Jonscher universal law, however LFDD is found to
be associated with quasi-DC process (QCD). The activation energies of DC
conduction confirm the mechanism as the thermal motion (short range hopping) of
doubly ionized oxygen vacancies. At high temperature, the conductivity
relaxation mechanism is dominated by grain boundary conduction through hopping
electron created by the charge compensating oxygen vacancies.
