The structural phase transition in PZT ferroelectric films

The Pb(Zr,Ti,W,Cd)O₃ (PZT) films were deposited by rf-sputtering of stoichiometric targets in an oxygen atmosphere. Epitaxial films had a tetragonal unit cell at room temperature. The unit cell parameter vs temperature curve showed a kink at phase transition temperature characteristic of the bulk material. Polycrystalline films had a pseudocubic unit cell. In spite of the presence of a full set of ferroelectric properties no anomalies in the temperature dependence of the unit cell parameter at phase transition were observed. The only evidence of the presence of the structural phase transition to a cubic phase was the essential decrease of intensity of X-ray reflections with an odd sum of indices as in the epitaxial films. These reflection intensities are most sensitive to the displacement of Zr and Ti cations with respect to Pb on approaching the Curie point temperature