Structure and Functional Properties of Epitaxial PbZrxTi1-xO3 Films
Prof. dr. ing. A.J.H.M. Rijnders / Prof. dr. ir. G. Koster
The work described in this thesis is focused on the characterization and understanding of epitaxial, clamped, dense PbZrxTi1-xO3 (PZT) films. A thermodynamic model is developed, which is used to simulate properties of clamped PZT films throughout this work. The free energy equations for single- and poly-domain films are given and allow us to simulate the material properties such as the piezoelectric coefficient, stress, strain, polarization and crystal phase of the PZT films. Experimental work done on tetragonal poly domain PbZr40Ti60O3 films is described. X-ray diffraction (XRD) measurements done with an applied field are used to measure the intrinsic piezoelectric coefficients of individual domains. The intrinsic piezoelectric coefficient of the domains in the PZT film is negative while the average piezoelectric coefficient of the film is positive, which is predicted by the model.
An alternative explanation for the origin of high piezoelectric coefficients using the new model is discussed. The model is used to explain the high piezoelectric characteristics of both film and bulk PZT found at the morphotropic phase boundary (MPB) using the characteristics of the rhombohedral and the tetragonal crystal phase or the phase change between them. The model also predicts that in principle arbitrarily high piezoelectric coefficients can be obtained in defect free films. The value of the coefficient is highly dependent on the misfit strain, which can be tuned using different substrates.
The structure of the domains and domain walls (DWs) in tetragonal PZT is explored. Data obtained using transmission electron microscopy shows that 2D films exist out of a c/a, c’/a’ domain structure. XRD and piezo force microscopy on 3D films show a complex c/a, c’/a’, c/b, c’/b’ domain structure which reconstructs when the out-of-plane polarization is switched. The complex domain structure can be explained as a mixed micro- and macro-domain structure that describes a domain structure which is required by our model.