Domain populations in lead zirconate titanate thin films of different compositions viapiezoresponse force microscopy

Abstract

Pb (ZrxTi1−x)O3 (PZT) thin films with (111) texture were deposited onto commercially availablePt/Ti/SiO2/Si substrates via the sol–gel technique. Piezoforce microscopy (PFM) was then usedto analyse the evolution of domain populations as a function of the Zr contentx. Domain structures of virgin films, local piezoelectric properties of individual grainsand piezoelectric histograms were studied in films with different compositions(x = 0.2–0.6), which cover both the tetragonal and rhombohedral sides of the phase diagram. In filmswith low Zr content mainly single-domain grains were observed. As the Zr content increased, alarger fraction of polydomain grains was found. The local piezoelectric response measured insidesufficiently big grains indicated that the strongest piezoelectric effect occurs in PZT30/70(x = 0.3) films. This was attributed to two different effects: high out-of-plane polarization achieveddue to the (111) texture and influence of the dielectric constant. In tetragonal filmswith their lower dielectric constants the electric field seen by a ferroelectric ishigher as compared to other compositions, giving rise to an apparent increaseof the effective piezoelectric response measured by PFM. The analysis of thedomain images indicated that sol–gel derived PZT films are slightly self-polarizednear the free surface. With increasing Zr/Ti ratio, the variation of domainpopulations resulted in reversing the sign of the average piezoelectric response atx≈0.3. It is demonstrated that PFM histograms are extremely sensitive to PZT composition andcan be used as a signature of complex domain structures in ferroelectric thin films.