Chemical ordering in lanthanum-doped lead magnesium niobate relaxor ferroelectrics probed by A(1g) Raman mode

Chemical ordering of the B-site cations in undoped, 5, 10, 20, and 30 mol % La3+-doped Pb(Mg1/3Nb2/3)O-3 (PMN) ceramics with perovskite structure, has been examined by Raman scattering. Two B-site chemical ordering models, th e space-charge model, and the random layer model assume a space group of Fm (3) over barm for the ordered nanoregions. It is found that A(1g) Raman mo de around 780 cm-1 from the B-site ordered nanoregions with a space group F m (3) over barm, is very sensitive to the delicate changes of the chemical order at B site. Frequency changes of this A(1g) characteristic mode with L a3+ doping, are analyzed according to the lattice parameters and chemical o rder effects. The present results provide stronge evidence supporting the r andom layer model in La-doped PMN. (C) 2001 American Institute of Physics.