DIFFUSED PHASE TRANSITION IN Pb 0.91(La 1− z/3 ,Li z) 0.09(Zr 0.65Ti 0.35) 0.9775O 3 CERAMICS

Abstract

The sol–gel process was used to prepare lithium-modified polycrystalline PLZT, Pb 0.91(La 1− z/3 ,Li z ) 0.09(Zr 0.65Ti 0.35) 0.9775O 3 ( z=0.0, 0.1, 0.3, 0.5, 0.7] (PLLZT), near the morphotropic phase boundary. X-ray diffraction studies of these compounds suggest that they can be formed in single phase at relatively low temperatures (∼800°C). The green pellets of these compounds were sintered at 1100°C. Detailed studies of the dielectric constant (ϵ) and loss tangent (tan δ) of PLLZT ceramics as a function of temperature (room temperature to 350°C) at 1 and 10 kHz frequencies suggest that the compounds exhibit relaxor behaviour and undergo ferroelectric phase transition of diffuse type on increasing the lithium concentration. Analysis of the broadened dielectric peaks of these compounds provided values of diffusivity (γ) between 1 and 2, which indicates the variation in the degree of disordering with change in z. The transition temperature ( T C) of the compounds was found to increase with increasing lithium concentration. The variation in the values of dielectric constant (ϵ) and loss tangent (tan δ) with lithium concentration shows very interesting behaviour of the compounds. The electrical conductivity and the activation energy of PLLZT provided some interesting results.