EFFECTS OF LANTHANUM MODIFICATION ON THE ANTIFERROELECTRIC-FERROELECTRIC STABILITY OF HIGH ZIRCONIUM CONTENT LEAD-ZIRCONATE-TITANATE

Lanthanum-modified lead zirconate titanate specimens with between 0 an d 9 at.% lanthanum and a Zr/Ti ratio of 95/5, Pb1-xLax(Zh(0.95)Ti(0.05 ))(1-x/4)O-3 (PLZT 100x/9515), have been investigated using dielectric spectroscopy, Sawyer-Tower polarization, and dilatometric measurement s. La modification was found to suppress the stability of the ferroele ctric state, changing the phase stability and phase sequence observed on cooling. PLZT 0/95/5 was found to be ferroelectric from room temper ature to the Curie point; however, an antiferroelectric state was foun d to be stabilized as the long-range ferroelectric state was disrupted by La substitution on the Pb sites. With increasing La content (>3 at .%), a multicell cubic (MCC) state was found to be stable near the tem perature of the dielectric maximum. This MCC phase region was characte rized by a dielectric plateau in the Curie temperature range and by th e lack of any macroscopic symmetry changes. It is suggested that compe tition between long-range ferroelectric and short-range antiferroelect ric couplings is responsible for the MCC state, changes in the relativ e phase stability, and subsequent changes in the macroscopic propertie s with increasing La content.