Study of Phase Transitions and Response of Dielectric Behavior of Pb1–1.5xLaxTiO3 Ceramics

Abstract

Polycrystalline samples of ferroelectric perovskite type lanthanum doped lead titanate, Pb1–1.5xLaxTiO3 (PLT) with x ranging from 0.00 ≤ x ≤ 0.3 ceramic system have been synthesized through the modified solid-state reaction technique. One of the objectives of this work was to optimize carefully the process variables which influence the structural and microstructural properties of the samples prepared. X-ray diffraction studies have been used to follow the evolution of the structural phases that occur with the increase of lanthanum content. The sharp peaks observed in XRD patterns and the absence of any impurity peaks confirmed the formation of single phase compounds. The analysis of the X-ray diffraction patterns for the samples with 0.00 ≤ x ≤ 0.2 confirmed the tetragonal phase formation. For x = 0.3 the observed X-ray diffraction peaks confirmed the presence of cubic phase as also evident from the absence of splitting of (101 110) and (002 200) peaks. The average linear particle sizes for all the compositions estimated using Scherrer's formula lie in the range 230–570 nm. The grain sizes of the lead lanthanum titanate ceramic powders increases with the increase of lanthanum content. The grain morphology and size were directly imaged using scanning electron microscopy (SEM) and the average grain size was determined by using a mean linear intercept method. Detailed studies of dielectric constant (ϵ) and tangent loss (tan δ) as a function of frequency (5 Hz–13 MHz) at room temperature (RT) and temperature (RT-900 K) suggest that compounds undergo ferroelectric-paraelectric phase transition of diffuse type. The value of diffusivity γ is extracted from the ln (1/ϵ−1/ϵmax) vs. ln (T−Tmax)γ plots and the values of γ vary between 1.18 to 1.75, which confirm that diffuse phase transition occurs in the lead lanthanum titanate (PLT) system. The results of differential scanning calorimetry (DSC) study also support the phase transition temperature observed in the dielectric measurements.