Dielectric properties of Pb(Mg1/3Nb2/3)O3 and (Pb1-xLax)(Mg(1+x)/3Nb(2-x)/3)O3 ceramics prepared by columbite route

The role of the La-addition on the A-site of the perovskite Pb(Mg1/3Nb2/3)O3 (PMN) on the phase formation, microstructure and dielectric properties was investigated. Ceramic samples were obtained from PMN and (Pb1-xLax)(Mg1+x/3Nb2-x/3)O3 (PLMN) nanopowders synthesized by the columbite method using MgO and Mg-carbonate precursors. An influence on the degree of crystallinity and phase purity was found particularly in the PMN ceramics. Typical relaxor properties characterised by a diffuse phase transition with a maximum around 270K and relaxation in the kHz range were observed. The incorporation of La induces the formation of a short range nanopolar ordered superstructure, thus modifying the dielectric relaxation properties, strongly depressing the permittivity. The observed behaviour is discussed in terms of microstructural characteristics induced by the Mg-precursor and of La-incorporation in the PMN perovskite unit cell.