Lanthanum induced diffuse phase transition in high energy mechanochemically processed and poled PLZT 8/60/40 ceramics

Abstract

La < sup > +3 < /sup > substitution based piezoelectric material, (Pb < inf > 0.92 < /inf > La < inf > 0.08 < /inf > ) (Zr < inf > 0.60 < /inf > Ti < inf > 0.40 < /inf > )O < inf > 3 < /inf > also known as PLZT 8/60/40, was prepared by high energy mechano-chemical ball milling. The highly reactive nature of the nano size (∼15-40 nm) milled PLZT powders enable the partial perovskite phase (confirmed by X-ray diffraction) at room temperature itself. Compaction of these fine scale nano powders by the cold isostatic pressing technique leads to a higher density > 98% with a close packed dense microstructure that can be seen in SEM images for sintered ceramics. Dielectric measurements for the electrically poled PLZT 8/60/40 ceramics suggest that the lanthanum substitution affects the nature of ferroelectric phase transition of PZT showing a deviation from normal to the diffuse type phase transition (DPT). The parameters of this DPT, such as degree of deviation from Curie-Weiss law (ΔT < inf > m < /inf > ), diffuseness empirical parameters γ and ΔT < inf > diff < /inf > were calculated at various frequencies from 1 kHz to 500 kHz. The large value of γ (1 < γ < 2) and ΔT < inf > diff < /inf > at said frequencies confirms the deviation from normal phase transition and the high degree of disorderliness in the material. To support this study, polarization vs. electric field and electromechanical coupling factor (k < inf > p < /inf > ) measurements were also performed on PLZT 8/60/40 ceramics within the temperature range of 30 °C-170 °C and 30 °C-210 °C respectively. The effect of temperature on the ferroelectric properties was also studied.