Mal. Nobre et S. Lanfredi, Phase transition in sodium lithium niobate polycrystal: an overview based on impedance spectroscopy, J PHYS CH S, 62(11), 2001, pp. 1999-2006
Structural phase transition of sodium lithium niobate Na0.88Li0.12NbO3 cera
mics was investigated by impedance spectroscopy. Electrical measurements we
re carried out in the frequency range 5-1.3 X 10(7) Hz. The reproducibility
of properties was investigated as a function of several thermal cycles, at
temperature ranges from 25 to 750 degreesC. The electric conductivity foll
ows the Arrhenius law, with two activation energies for the conduction, not
associated to ferroelectric Curie temperature, derived at around 640 degre
esC. Both branches of the conductivity curves depend on the step (heating o
r cooling cycle) and the number of thermal cycles. Simultaneous dependence
of the permittivity on temperature was observed. Three phase transitions un
der 540 degreesC, displaying distinct overlapping degrees, were proposed. O
ne additional transition is proposed at around 640 degreesC. The nonreprodu
cibility of conductivity and dielectric properties as function of phase tra
nsition phenomenon is discussed. (C) 2001 Elsevier Science Ltd. All rights
reserved.