Substitution site effect on structural and dielectric properties of La–Bi modified PZT

Substitution site effect of (La:Bi) on the structural and dielectric properties of chemically prepared PZT system Pb_0.92 (La_1−x Bi _x ) _0.08(Zr_0.65Ti_0.35)_0.98O₃ (a) x = 0.0, (b) x = 0.1, (c) x = 0.2, (d) x = 0.3, (e) x = 0.4 and (f) x = 1.0] have been studied. The samples were prepared by employing a simple co-precipitation technique using nitrates of lead, lanthanum, bismuth, zirconium and titanium isopropoxide. X-ray diffraction studies confirm the formation of phase pure and homogeneous ceramics of rhombohedral symmetry without bismuth addition and a tetragonal symmetry was confirmed for the compounds containing bismuth due to the presence of a doublet (200) peak in these compounds. Scanning electron micrographs shows a uniform grain distribution and the grain size and shape were modified upon bismuth addition. Increase in Bi content causes a decrease in average grain size of the material. Dielectric measurements demonstrate a diffuse type of phase transition and this diffuseness decreases with increasing Bi ion concentration. Composition (A) only showed relaxor type of behaviour. Variation of dielectric constant with temperature shows that both T _c and ε_max increases with increase of Bi concentration. This was explained on the basis of favorable B-site substitution of Bi⁺³ ions and therefore the increased strength of spontaneous polarization. Finally, it is evident that the type of substitution site also has a significant effect on the dielectric properties of the PZT system. All these results suggest that the synthesized ceramics may be suitable for device applications.