Ferroelectric and glassy states in La-modified lead zirconate titanate ceramics: A general picture

• Published in: Journal of applied physics 1998-05, Vol.83 (10), p.5371-5380
• Main Authors: El Marssi, M., Farhi, R., Dellis, J.-L., Glinchuk, M. D., Seguin, L., Viehland, D.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.367366

Raman scattering, pyroelectric current, and dielectric susceptibility measurements have been carried out on a series of tetragonal and rhombohedral-structured Pb1−xLax(ZryTi1−y)1−x/4O3 (PLZT) ceramics, under zero-field heating after zero-field cooling (ZFH/ZFC) and zero-field heating after field-cooling (ZFH/FC) conditions. The results have been shown to be in good agreement with previous transmission electron microscopy observations. A dependence of the Raman spectra on light polarization (i.e., Raman selection rules or RSR), which are known to be a characteristic property of single crystals, has been observed in the PLZT compositions 9/65/35, 12/65/35, 6/40/60, and 12/40/60 illuminated with a 2 μm wide laser spot (i.e., micro-Raman). The texture which has been observed by x-ray diffraction on 6/40/60 is discussed in conjunction with the Raman results. The combined data of Raman scattering experiments and electrical measurements, together with electromechanical and ferroelectric properties, are explained in terms of competing random fields. Furthermore, the disappearance of RSR in the ZFH/FC conditions for the ferroelectric relaxor PLZT 9/65/35 has given evidence for the existence of domains and grain boundaries in the field cooled conditions. Similar Raman spectra were found for the ferroelectric PLZT composition 5/65/35 in zero-field conditions. The occurrence of RSR in PLZT x/65/35 for x>8 (i.e., for only relaxor states with average cubic symmetry) are interpreted as resulting from second-order scattering effects. This supports a model of a cluster glass with short-range-ordered polar clusters rather than a multidomain state (i.e., a multitude of small ferroelectric domains) in these relaxor systems.