Pair Distribution Function: a B cation disorder in cerium doped BaTiO3

Perovskite-like compounds exhibit a variety of exploitable properties that can be chemically tuned using substitutions on the A, B or both cation sites of the ABO3 perovskite structure [1]. BaTiO3 is considered an environmental-friend ferroelectric: chemical substitutions at the Ba2+ and/or Ti4+ sites are in fact usually made to tailor properties for a variety of device and performance requirements [2]. A classical example is the solid solution BaTi1-xMIVxO3, where M could be Sn, Zr, Hf, Ce etc., whose ferroelectric behavior shows an almost continuous variation with composition [3]. The reason for this is, usually, that distinct B cations mixed on the octahedral sites form ordered arrangements, and the properties of complex perovskites are strongly affected by the type, degree and spatial extent of this order [4]. In this work attention has been focused on BaTi1-xCexO3 ceramic solid solutions. It represents a limit and interesting case due to a large difference in the Ti and Ce ionic radius ( rCe4+ = 0.87 Å and rTi4+= 0.605 Å), and it is a substitution that does not involve the creation of charge compensating lattice defects. Three samples with different cerium amount and three different polar behavior has been chosen: conventional ferroelectric (x = 0.05) but close to the so-called pinched transition, diffuse phase transition (x = 0.10) and non-ergodic relaxor (x = 0.20). In order to model the local structure and in particular to explore the local neighbourhood relation between cerium and titanium, refinements have been performed using Pair Distribution Function technique. With the aim of confirming PDF results, lattice energies have been furthermore calculated and compared for different structural configurations: from random distribution to a clustered supercell. Different numbers and size of BaCeO3 clusters have been considered and discussed. [1] Krayzman V., Levin I. and Tucker M.G. Journal of Applied Crystallography, 2008, 41, 4. [2] Maiti T., Guo R. and Bhalla A.S. Journal of the American Ceramic Society, 2008, 91, 6. [3] Shvartsman V.V., Lupascu D.C., Journal of the American Ceramic Society, 2012, 95, 1. [4] Krayzman V. and Levin I. Journal of Applied Crystallography, 2008, 41, 2.