Response of the ferroelectric domain structure of morphotropic PZT to the application of an electric field – in-situ synchrotron X-ray diffraction

The origin of the extremely high piezoelectric response of morphotropic ferroelectric lead zirconate titanate (PZT), PbZr(1-x)Ti(x)O3, is still under discussion. Noheda et al. [1] proposed a monoclinic phase at the morphotropic phase boundary (MPB) as an explanation, via which a rotation of the polarization direction is possible. However, interpretation of X-ray data so far has not taken into account the strongly varying domain structure across the MPB.We have undertaken roomtemperature and temperature-dependent synchrotron X-ray powder diffraction experiments with and without an applied electric field.Acomplete series of polycrystalline pellet samples across the MPB was analysed in transmission mode geometry in high-resolution and intermediate resolution image plate setup at B2, Hasylab Hamburg, Germany and also subjected to TEM imaging. The investigations show that the domain structure miniaturizes across the MPB down to nanodomains of 5-10nm width and as a consequence the diffraction patterns depict a strong increase in peak asymmetry as the tetragonal c/a-ratio decreases with increasing Zr content. These nanodomains appear in the same stability range as the proposed monoclinic phase. The existence of a monoclinic phase, however, is questioned by Jin et al. [2] for relaxor ceramics, assuming that it is just an effect of domain miniaturization and coherence in diffraction. The changes in domain structure have a dramatic influence on the poling behaviour of the material. While compositions at the edges of the MPB only show changes in domain orientation along the applied field, morphotropic samples exhibit strong changes in both lattice constants and intensities, accompanied by a strong increase in macroscopic strain. PZT 54/46 shows an increase in the intensity between the tetragonal 101 / 110 duplet under electric field and seems textured rhombohedral in-situ under 5kV/mm. The effects observed will be discussed in terms of reorientation of nanodomains through changes in domain configuration, stacking disorder, polarization rotation and possible phase transitions under electric field. The authors appreciate the financial support of the German Research Foundation (DFG) through the Sonderforschungsbereich 595 ’’Electric fatigue in functional materials’’ and the virtual institute (VH-VI-102) of the Helmholtz Society. [1] B. Noheda, J.A. Gonzalo, L.E. Cross, R. Guo, S.E. Park, D.E. Cox, G. Shirane, Phys. Rev. B, 61, 8687 (2000). [2] Y.M. Jin, Y.U. Wang, A.G. Khachaturyan, J.F. Li, D. Viehland, Phys. Rev. Lett. 91, 197601 (2003)