COMPARATIVE-STUDY OF THE ORDERING OF B-SITE CATIONS IN PB2SCTAO6 AND PB2SCNBO6 PEROVSKITES

A comparative study of as-grown Pb2ScTaO6 and Pb2ScNbO6 crystals obtained under similar conditions is made by X-ray and electron diffraction and by HREM at room temperature. From this study it can be concluded that: (i) the average distribution of atoms gives a cubic unit cell for both compounds though the study is conducted at a temperature close to T(c) for PST, and lower than T(c) for PSN; (ii) PST and PSN present the classical {111}-type ordering and PST material has always a higher degree of ordering than PSN when they are prepared under similar conditions; (iii) small domains of {110}-type ordering are observed in these two compounds leading to supplementary reflections, even by X-ray diffraction in the case of PSN.