Ferroelectric phase transition in sol-gel derived Bi-doped PLZT ceramics

Abstract

Polycrystalline samples of Bi-modified PLZT, [Pb0.92(La1−zBiz)0.08][Zr0.60Ti0.40]0.98O3 (abbreviated as PLBZT) for z = 0.0, 0.3, 0.6, 0.9 and 1 were prepared through a metal-alkoxide/sol-gel route. Preliminary X-ray diffraction study of the compounds confirmed the formation of single-phase tetragonal compounds. Scanning electron-microscopic (SEM) study of pellet samples of PLBZT shows uniform distribution of grains (spherical) throughout the sample surfaces. Detailed studies of dielectric parameters (dielectric constant, tangent loss) of PLBZT as a function of temperature (30 to 450°C) at 10 kHz reveal that the compounds have diffuse phase transitions. Large variation (first increase and then decrease) in dielectric constant and shift of transition temperature towards higher temperature side with increasing Bi concentration was also observed in PLBZT. The nature of variation of dc resistivity shows that the titled compounds have negative temperature coefficient of resistance (NTCR). Pyroelectric coefficient of the PLBZT compound (z = 0.0 to 1.0) increases with increase of Bi content in PLZT. The transition temperature obtained in this study is very much consistent with that obtained from our dielectric studies. Piezoelectric d33 coefficient of the compound at 100 Hz was found to be 385, 272, 301, 248 and 291 pc/N for z = 0.0, 0.3, 0.6, 0.9 and 1 respectively.