ROLE OF CHARGE COMPENSATION MECHANISM IN LA-MODIFIED PB(MG1 3NB2/3)O-3-PBTIO3 CERAMICS - ENHANCED ORDERING AND PYROCHLORE FORMATION/

Selected area electron-diffraction (SAED) investigations were performe d on La-modified (1-x)Pb(Mg1/3Nb2/3)O-3-x(PbTiO3) ceramics for composi tions near the morphotropic phase boundary for various nonstoichiometr ic ordering conditions of Mg and Nb on the B-site cation positions. St udies were performed on specimens with La contents between 0 and 10 at . % and for x=0.35. Specimens were fabricated either by: (i) keeping t he average Mg/Nb/Ti ratio unchanged and while creating B-site vacancie s (La-PMN-PT), or (ii) changing the average Mg/Nb/Ti ratio (PLMN-PT). For La-PMN-PT, SAED studies revealed the presence of F spots for high La contents. The superlattice reflection intensity was found to increa se with increasing La content. However, for PLMN-PT, distinct diffuse superlattice reflections were observed at low La contents, which then decreased significantly in intensity with increasing La substitution. Quantitative analysis using standardless energy-dispersive x-ray spect roscopy was also performed. These investigations revealed that enhance d pyrochlore formation accompanies enhanced B-site cation ordering wit h increasing La content for La-PMN-PT. (C) 1996 American Institute of Physics.