Ba(Ti,Ce)O3 solid solution: the relationship between composition, grain size, and structural properties

BaTiO3 perovskite and its solid solutions are nowadays the most used ferroelectric materials, being them environmental friendly and with excellent properties. Among the various possible solid solutions with homovalent substitution at Ti site (BaTi1-xMIVxO3), only BaTi1-xZrxO3 was studied extensively from the structural point of view [1]. Other substitutions can be interesting: in particular, the one with cerium, BaCexTi1-xO3 (BCT), which presents a large difference in size between Ti and Ce ions. Therefore, in this work, BCT with different Ce amount (x=0.02-0.20) and various particle sizes (from 80-160 nm to 5 um) was deeply explored both on the average and on the local structure by means of traditional Rietveld method and Pair Distribution Function. BCT in its ceramic form (grain size: 1 to 5 um) presents a polar behaviour variation from conventional ferroelectric to relaxor via diffuse phase transition (DPT) [2, 3]. As the particle size is reduced, the so called "size effect" takes over, with larger variations in the electric properties with composition. It is well known that ferroelectricity is related to titanium displacement within the octahedra, and our Rietveld analysis results find a good agreement between measured material properties and titanium offcenter values in the ceramic materials. The progressive suppression of the spontaneous polarization with x and the cubic phase stabilization is related to the disruption of the correlated Ti displacements engendered by the large Ce4+ incorporated at the octahedral site [4], and a complex model must be used for the local structure. All the described effects are generally more pronounced when the material presents a reduced particle size, as cerium content and reduced size cooperate in the extension of the cubic structure stability field, with respect to the corresponding micrometric materials. The distortions at the local level are therefore confirmed to be largely responsible for the ferroelectric properties of the BaCexTi1-xO3 perovskite, either in the micrometric or in the reduced size samples. [1] V. Buscaglia, S. Tripathi, V. Petkov, M. Dapiaggi, M. Deluca, A. Gajovic, Y. Ren, J. Phys. Condens. Matter 26 (2014), 065901. [2] V.V. Shvartsman, D.C. Lupascu, J. Am. Ceram. Soc. 95 (2012), 1. [3] G. Canu, G. Confalonieri, M. Deluca, L. Curecheriu, M.T. Buscaglia, M. Asandulesa, N. Horchidan, M. Dapiaggi, L. Mitoseriu, V. Buscaglia, Acta Mater. 152 (2018), 258. [4] G. Confalonieri, V. Buscaglia, G. Capitani, G. Canu, N. Rotiroti, A. Bernasconi, A. Pavese & M. Dapiaggi, J. Appl. Cryst 51 (2018), 1283.