Influence of B-site chemical ordering on the dielectric response of the Pb(Sc1/2Nb1/2)O-3 relaxor

The influence of chemical B-site ordering between Sc3+ and Nb5+ cations on the properties of the Pb(Sc1/2Nb1/2)O-3 (PSN) relaxor has been investigated . Depending of the degree of ordering, PSN exhibits different behaviours. F or a completely disordered material, a relaxor-ferroelectric phase transiti on is observed at 379 K by DSC. Ordering between Sc3+ and Nb5+ cations on t he B-site of the perovskite structure leads to a non-homogeneous material c onstituted of two phases: ordered and disordered phases. The phase transiti on temperature of the ordered phase is confirmed to be lower (346 K) than t hat of the disordered phase. It appears that the phase transition of the di sordered phase is shifted to lower temperature owing to the presence of the ordered phase. Moreover, an additional short-range structural ordering is shown to exist i n disordered PSN. This additional ordering, for which antiparallel displace ments of Ph atoms could be involved, is favoured by chemical ordering betwe en Sc3+ and Nb5+ and is long range in ordered PSN.