FERROELECTRIC AND GLASSY STATES IN LA-MODIFIED LEAD-ZIRCONATE-TITANATE CERAMICS - A GENERAL PICTURE

Raman scattering, pyroelectric current, and dielectric susceptibility measurements have been carried out on a series of tetragonal and rhomb ohedral-structured Pb1-xLax(ZryTi1-y)(1-x/4)O-3 (PLZT) ceramics, under zero-field heating after zero-field cooling (ZFH/ZFC) and zero-held h eating after held-cooling (ZFH/FC) conditions. The results have been s hown to be in good agreement with previous transmission electron micro scopy observations. A dependence of the Raman spectra on light polariz ation (i.e., Raman selection rules or RSR), which are known to be a ch aracteristic property of single crystals, has been observed in the PLZ T compositions 9/65/35, 12/65/35, 6/40/60, and 12/40/60 illuminated wi th a 2 mu m wide laser spot (i.e., micro-Raman). The texture which has been observed by x-ray diffraction on 6/40/60 is discussed in conjunc tion with the Raman results. The combined data of Raman scattering exp eriments and electrical measurements, together with electromechanical and ferroelectric properties, are explained in terms of competing rand om fields. Furthermore, the disappearance of RSR in the ZFH/FC conditi ons for the ferroelectric relaxer PLZT 9/65/35 has given evidence for the existence of domains and grain boundaries in the field cooled cond itions. Similar Raman spectra were found for the ferroelectric PLZT co mposition 5/65/35 in zero-field conditions. The occurrence of RSR in P LZT x/65/35 for x > 8 (i.e., for only relaxer states with average cubi c symmetry) are interpreted as resulting from second-order scattering effects. This supports a model of a cluster glass with short-range-ord ered polar clusters rather than a multidomain state (i.e., a multitude of small ferroelectric domains) in these relaxer systems. (C) 1998 Am erican Institute of Physics.