Influence of Fluorine Co-Doping on the Properties of Cationic Doped PZT Ceramics. Effect on the Valency State of Acceptor and Donor Dopants

Abstract

Recently, it has been shown that co-doping with 1% mol. Manganese and 1% mol. fluorine a PZT base composition improved the dielectric and piezoelectric properties. A model based upon electron transfers between Mnα + ions (α = 2, 3, 4) has been proposed to explain such a behaviour. F co-doping has been realized on Cr and Sn doped PZT to determine if the same model is valid with other acceptor dopants possibly exhibiting different valency states in the PZT. (Sb, F) and (Nb, F) co-doped PZTs were also studied to estimate the influence of fluorine on the valency state of donor dopants. XRD measurements revealed that F co-doping generates lead vacancies in the cationic sublattice of Cr doped PZT instead of partially reducing cationic dopant. No change is observed in the unit cell volume and the piezoelectric properties of Sb and Nb doped PZTs after F co-doping. In the case of Sn doping, F− ion may make Sn 2+ and Sn 4+ coexist in the PZT but the characteristics are not as high as (Mn, F) co-doped PZT ones. The correlation between cubic unit cell volume and lead vacancies content in the PZTs was supported by flame Atomic Absorption measurements. The study confirms that the softening effect observed is not due to the increase of extrinsic lead vacancies content but to the coexistence of three valency states of the cationic dopant like Mn+ 4, + 3, + 2 .