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

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 d_ij and e_ij, 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 e_31,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.