Phase transition in sodium lithium niobate polycrystal: an overview based on impedance spectroscopy

Structural phase transition of sodium lithium niobate Na0.88Li0.12NbO3 ceramics was investigated by impedance spectroscopy. Electrical measurements were carried out in the frequency range 5-1.3×107 Hz. The reproducibility of properties was investigated as a function of several thermal cycles, at temperature ranges from 25 to 750°C. The electric conductivity follows the Arrhenius law, with two activation energies for the conduction, not associated to ferroelectric Curie temperature, derived at around 640°C. Both branches of the conductivity curves depend on the step (heating or cooling cycle) and the number of thermal cycles. Simultaneous dependence of the permittivity on temperature was observed. Three phase transitions under 540°C, displaying distinct overlapping degrees, were proposed. One additional transition is proposed at around 640°C. The non-reproducibility of conductivity and dielectric properties as function of phase transition phenomenon is discussed.