Niobium doped lead zirconate titanate thin films grown by chemical solution deposition

Abstract

Niobium (Nb) doping is known to have a beneficial effect on many properties of lead zirconate titanate (PZT) ceramics. Substituting titanium (Ti) or zirconium (Zr) on a B-site, Nb ions form positive point defects that repel oxygen vacancies, even though they are compensated by negative lead (Pb) vacancies of half their concentration. As a consequence, PZT domains are known to move more easily. Nb doped ceramics excel in high piezoelectric coefficients dij and eij, and high permittivities. In this work, we investigated concentration gradient issues, dielectric, ferroelectric, and piezoelectric properties of Nb doped, {100}-textured PZT thin films. The {100}-texture could be maintained throughout the investigated compositional range. As it is known that sol-gel processing tends to form Zr/Ti gradients, it was of interest to know whether Nb forms gradients, and if yes, in which direction. We observed a behaviour similar to one of Zr, an enrichment away from where nucleation happens, thus the top part of the layer. The transverse piezoelectric coefficient e31,f was measured in the direct mode at zero electric field, and in the converse mode as a function of the electric field. The Nb doped films exhibited higher dielectric constants and higher break-down fields, but lower remnant polarizations because of enhanced backs-switching. As compared to “standard” sol-gel PZT films, they show an increased piezoelectric performance at high fields and improved reliability.