CATIONIC ORDERING IN LEAD SAMARIUM MAGNESIUM NIOBATE

Pyrochlore-free Sm2O3-doped/undoped Pb(Mg1/3Nb2/3)O-3 ceramics were fa bricated and their cationic ordering structures were investigated by X RD and TEM. In the X-ray diffraction patterns, only fundamental diffra ction peaks were observed for the undoped Pb(Mg1/3Nb2/3)O-3, while the (h+1/2 k+1/2 1+1/2) superlattice reflections were also observed for t he Sm2O3-doped Pb(Mg(1/3)nTb(2/3))O-3 In the SAED patterns, the (h+1/2 k+1/2 1+1/2) superlattice reflections as well as the fundamental diff raction spots were observed for both of the undoped and the Sm2O3-dope d Pb(Mg1/3Nb2/3)O-3, but the intensities of the superlattice reflectio ns were stronger for the Sm2O3-doped Pb(Mg1/3Nb2/3)O-3. In the centere d dark-field images, ordered domains of > 50 nm were observed only for the Sm2O3-doped Pb(Mg1/3Nb2/3)O-3 It has been therefore experimentall y assured that the Sm2O3-doping enhances the 1:1 ordering of Mg2+ and Nb5+ ions in Pb(Mg1/3Nb2/3)O-3. These experimental results are discuss ed on the basis of charge compensation mechanism.