A quantitative study was made of the thickness dependence of polarization and piezoelectric properties in epitaxial (001) PbZr0.52Ti0.48O3 films grown onto (001) SrRuO3-buffered (001)SrTiO3 substrates. High-resolution transmission electron microscopy revealed that even the thinnest films (about 8nm) were fully relaxed; with a dislocation density close to 1012/cm2 and a spacing of about 12nm. Quantitative piezoelectric and ferroelectric measurements revealed a marked degradation of the out-of-plane piezoelectric constant, and switched polarization as a function of decreasing thickness. On the other hand, lattice-matched ultra-thin PbZr0.2Ti0.8O3 films that had a very low dislocation density exhibited superior ferroelectric properties. Theoretical calculations showed that variations in the strain field around the core of the dislocation led to highly localized polarization gradients and thus strong depolarizing fields; which resulted in suppression of ferroelectricity in the vicinity of a dislocation.

Misfit Dislocations in Nanoscale Ferro-Electric Heterostructures. V.Nagarajan, C.L.Jia, H.Kohlstedt, R.Waser, I.B.Misirlioglu, S.P.Alpay, R.Ramesh: Applied Physics Letters, 2005, 86[19], 192910 (3pp)