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Density-functional theory calculations are performed to examine how two characteristics of a trivalent dopant (the one, physical – the ionic radius, the other, chemical – the electronegativity) impact the thermodynamics of doping, the defect association energy and the hydration energy in barium stannate, a perovskite oxide candidate as an electrolyte for Solid Oxide or Protonic Ceramic Fuel Cells. The formation energies of several trivalent dopants currently used in experimental works are computed in different external conditions and on the two possible sites (Ba, Sn), in their ionized state. These dopants cover a wide range of ionic radii (from 0.62 to 1.03 Å) and can be divided in two families according to their electronegativity: elements of group IIIA (Ga, In), versus IIIB transitions metals and Rare Earths (Sc, Lu, Y, Gd, Sm, La). The oxygen vacancy and the protonic defect are also studied, either isolated or in the vicinity of the dopant substituted on Sn site (1st & 2nd neighbors). The association energy between the dopant and both the oxygen vacancy and the proton, as well as the formation energy of the dopant on the Ba site, are mainly governed by the ionic radius of the dopant, with the exception that electronegative dopants stabilize more the oxygen vacancy in their vicinity. Therefore, a subtle interplay between elastic effects and chemistry is found to control the hydration energy/enthalpy, the more electronegative dopants – indium particularly – producing, at given radius, a less stable hydrated state . We provide with general trends likely to help experimentalists in the design of new materials, regarding the choice of dopant. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we present a complete study of BaSn1−xYxO3−δ (x=0–0.50) compounds putting emphasis on transport properties as determined by impedance spectroscopy under controlled atmosphere. The measurements of transport properties reveal a p-type behavior in oxidative atmosphere and a pure ionic behavior in slightly reducing one. In strongly reducing conditions, the samples tend to be electron-conductive at high temperature. In wet atmosphere, the thermogravimetry and electrical measurements confirm the incorporation of protons and their predominance as charge carrier at low temperature. The higher bulk proton conductivities are observed for the higher yttrium contents, which is due to the increased amount of charge carriers. After applying different thermal treatments, we confirm that these samples tend to decompose in wet conditions and that low yttrium contents are desirable to increase the stability. The good stability in CO2-containing atmosphere is also confirmed. This work illustrates that an optimal value for yttrium content exists that allows obtaining a significant proton conductivity and sufficient stability. [Copyright &y& Elsevier]

Abstract: Electrical behaviour of compositions with x ≤0.100 in the BaSn1−x Nb x O3 system has been studied by employing complex impedance method in the temperature range 300–500 K and in the frequency range 100 Hz–10 MHz. An equivalent electrical circuit model, which contains a series arrangement of two parallel RC elements, is proposed to represent the electrical characteristics of the material. These studies show the contributions of two processes to the electrical conductivity, which are attributed to the activated hopping processes within the bulk. Electrical conduction behaviour has been explained in terms of the defect structure model. [Copyright &y& Elsevier]