Calcium substituting B-site in relaxor ferroelectrics with perovskite structure probed by chemical ordering

Chemical ordering of Ca2+ doped 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 ceramics were investigated by dielectric spectra, TEM diffraction and A1g mode in Raman spectra. It is found degree of relaxor behavior increases first, and then decreases. It conflicts the prediction Ca2+ substitutes for A-site ion Pb2+ according to crystal chemistry theory. In this letter, a new mechanism that Ca2+ substitutes for B-site ions has been proposed, which satisfactorily explained change of chemical ordering. It exhibits strong evidence doped ions with larger ionic radius (Ca2+) are quite possibly substitute much smaller ones (Nb5+ or Ti4+) in B-site rather than all substitute larger A-site ion in relaxor ferroelectrics.