Effect of rare earth (Er, Gd, Eu, Nd and La) and bismuth additives on the mechanical and piezoelectric properties of lead zirconate titanate ceramics

Mechanical, piezoelectric and dielectric properties of PZT ceramics (Pb0.98M0.02[(Zr0.535Ti0.465)0.995]O3, M=Er, Gd, Eu, Nd, La and Bi) have been studied. The fraction of A sites occupied by the different additives is estimated and is found to increase with the ionic radius of the additive ion. The density is high in Bi-, Gd- and Eu-PZT samples. Small amounts of the pyrochlore phase are present in Gd- and Eu-PZT. A maximum strength of 80–100 MPa and KIC of ∼1.5 MPa m1/2 are obtained in Gd- and Eu-PZT. The R-curve behavior becomes more pronounced in Gd- and Eu-PZT, and it is observed that the strength and KIC increase with the slope of the KIC versus c1/2 plot. Very good piezoelectric properties, i.e. d33 of 410 PCN−1, dielectric constant of 1005, κp of 0.49 and the hydrophone figure of merit, dhgh, of 2760 are obtained for Nd-PZT. The piezoelectric properties in Bi-PZT are also higher than for the undoped composition, while for the Gd-PZT, these are slightly inferior. For all other compositions, the piezoelectric properties are not affected much.