Role of charge compensation mechanism in La-modified Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics: Enhanced ordering and pyrochlore formation

Selected area electron-diffraction (SAED) investigations were performed on La-modified (1−x)Pb(Mg1/3Nb2/3)O3–x(PbTiO3) ceramics for compositions near the morphotropic phase boundary for various nonstoichiometric ordering conditions of Mg and Nb on the B-site cation positions. Studies were performed on specimens with La contents between 0 and 10 at. % and for x=0.35. Specimens were fabricated either by: (i) keeping the average Mg/Nb/Ti ratio unchanged and while creating B-site vacancies (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 increase 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 spectroscopy was also performed. These investigations revealed that enhanced pyrochlore formation accompanies enhanced B-site cation ordering with increasing La content for La–PMN–PT.