Effect of A Site Substitution on Order-Disorder Transition in Pb(Fe<sub>1/2</sub>Nb<sub>1/2</sub>)O<sub>3</sub>(PFN) and Pb(Sc<sub>1/2</sub>Ta<sub>1/2</sub>)O<sub>3</sub> (PST)

Abstract

The effect of A site substitution of Pb(Fe1/2Nb1/2)O3 (PFN) and Pb(Sc1/2Ta1/2)O3 (PST) with Na or La on the order-disorder transition and dielectric characteristics was examined. It was clarified that the degree of ordering at the B site did not change by the substitution though it has been reported that in case of Pb(Mg1/3Nb2/3)O3 (PMN), the degree of ordering can be controlled by the A site substitution. The reason may be due to the difference in cation size ratio of B site, that is, Mg:Nb=1:2 for PMN and Fe:Nb and Sc:Ta=1:1 for PFN and PST. By partial substitution of A site by La or Na, the dielectric characteristics of PFN and PST drastically changed from normal ferroelectric to “relaxor ferroelectric”. This indicates that “relaxor ferroelectrics” can not be necessarily derived from the order-disorder state at the B site sublattice as understood so far. The “relaxor ferroelectric” property of Na or La doped PST and PFN would be classified into the same group of (Pb, La) (Zr, Ti)O3 (PLZT) and La doped (Sr, Ba)Nb2O6 (SBN).