Effect of lithium carbonate doping on microstructure and electrical properties of PFN-PNN-PZT ceramics

(1-x)Pb[(Fe1/2Nb1/2)0.1 (Ni1/3Nb2/3)0.45 (Zr0.3Ti0.7)0.45] O3-xLi2CO3 (PFN-PNN-PZT-xLi, x=0, 0.5%, 1.0%, 1.5%, 2.0%) piezoelectric ceramics were prepared by a conventional solid-state reaction method. The effect of Li2CO3 content on the microstructure, phase structure, dielectric, piezoelectric, and ferroelectric properties of PFN-PNN-PZT ceramics was investigated. The analysis by X-ray diffraction and scanning electron microscopy indicates that the as-prepared ceramics are a pure perovskite structure phase without any other second phases, and their crystal structures transform from rhombohedral to tetragonal with increasing Li2CO3 content. The measurements of electrical properties show that the doping of Li2CO3 does not affect the change of the Curie temperature (Tm), but improve the temperature stability of dielectric constant (γ). Moreover, the piezoelectric constant (d33) and electromechanical coupling coefficient (kp) decrease, but the mechanical quality factor Qm and the coercive field (Ec) increases with increasing Li2CO3 content. The doping of Li2CO3 has a dominant effect on the properties of PFN-PNN-PZT ceramics. The ceramic with x of 1.5% sintered 1200°C for 2 h exhibits the favorable electrical properties and superior temperature stability (i.e., d33=820 pC/N, kp=0.63, relative dielectric constant Εr=6628, tan δ=0.028, temperature coefficient of dielectric constant γ=17%, Qm=52.6, and Ec=4.48 kV/cm).