Direct Imaging of Atomic Ordering in Undoped and La-Doped Pb(Mg1/3Nb2/3)O3

• Published in: Journal of the American Ceramic Society 2000-01, Vol.83 (1), p.181-88
• Main Authors: Xu, Zhengkui, Gupta, Surya M., Viehland, Dwight, Yan, Yanfa, Pennycook, Stephen J.
• Format: Article
• Language: English
• Subjects: Cations; Ceramics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Dielectric, piezoelectric, ferroelectric and antiferroelectric materials; Dielectrics, piezoelectrics, and ferroelectrics and their properties; dopants/doping; Exact sciences and technology; Imaging; Inorganic compounds; lanthanum; lead magnesium niobates; Magnesium; Niobates, titanates, tantalates, pzt ceramics, etc; Niobium; Order disorder; Physics; Relaxors; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Water, oxides, hydroxides, peroxides
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.2000.tb01168.x

In this paper, we report the first direct observations of local ordering in undoped and La‐doped Pb(Mg1/3Nb2/3)O3 (PMN) on an atomic scale by high‐resolution (∼1.26 Å) Z‐contrast imaging. The 1:1 ordering occurs by a variation in the occupancy of Mg and Nb cations between BI and BII sublattices. In ordered regions, the BII sublattice is dominantly occupied by Nb cations, but a small Mg occupancy cannot be excluded. The Mg cations were found to dominantly occupy the BI sublattice. Within the BI sublattice, the local Mg/Nb ratio was found to vary among the various BI sublattices. The results show that the random‐site model, rather than the space‐charge model, is a better structural model for the 1:1 ordering observed in PMN. A random distribution of Mg and Nb cations on the BI sublattice within 1:1 ordered regions is believed to be responsible for the relaxor behavior of mixed B‐site cation relaxors, such as PMN.