Defect chemistry and transport properties of Ba_xCe_0.85M_0.15O_3-δ

Abstract

The site-incorporation mechanism of M 3+ dopants into A 2+ B 4+ O 3 perovskites controls the overall defect chemistry and thus their transport properties. For charge-balance reasons, incorporation onto the A 2+ -site would require the creation of negatively charged point defects (such as cation vacancies), whereas incorporation onto the B 4+ -site is accompanied by the generation of positively charged defects, typically oxygen vacancies. Oxygen-vacancy content, in turn, is relevant to proton-conducting oxides in which protons are introduced via the dissolution of hydroxyl ions at vacant oxygen sites. We propose here, on the basis of x-ray powder diffraction studies, electron microscopy, chemical analysis, thermal gravimetric analysis, and alternating current impedance spectroscopy, that nominally B-site doped barium cerate can exhibit dopant partitioning as a consequence of barium evaporation at elevated temperatures.

Processing of yttrium-doped barium zirconate for high proton conductivity

“…Such behavior is now well documented in barium-deficient, rare-earthdoped barium cerate. [24][25][26] Alternatively, the behavior may result from a reduction of the dopant content in the perovskite with yttria being expelled from the structure to maintain an A-to-B stoichiometric ratio of 1 to 1. In contrast to the uncovered samples, after even 24 h of exposure to this same temperature BYZ20 covered with excess powder of the same composition is free of yttria precipitates.…”

“…A discussion of the grain-boundary properties of these samples is presented elsewhere. 29 The detrimental impact of barium deficiency on the conductivity of doped barium cerate has been well documented 24,25 and explained in terms of the occupation of the trivalent dopant on the A rather than the B site. These effects, which occur in single-phase materials, are responsible for variations in bulk conductivity by a factor of 2 to 3.…”

Performance and stability of proton conducting solid oxide fuel cells based on yttrium-doped barium cerate-zirconate thin-film electrolyte

“…4(b) shows the detailed peak shifts of BCZY and BSCF heat-treated at high temperatures. The diffraction patterns of BCZY heat-treated at high temperatures over 900 ºC show peak shift towards higher 2 theta, indicating a smaller unit cell volume than the stoichiometric compound, resulting from the loss of BaO at high temperatures [47]. Ba-deficient doped barium cerate formed by the loss of BaO can readily incorporate a B-site doping element with a smaller ionic radius than Ba 2+ onto the A-site as described by the equation (4), resulting in the decrease of a unit cell volume [48].…”

“…If it is assumed that Y or Zr in B-site can be also diffused to BSCF to form Y/Zr doped B-site cation-rich BSCF, the peaks of A-site cation-rich BCZY should be slightly shifted towards lower 2 theta in the diffraction patterns due to the increase of the unit cell volume [47,49].…”

Correlation between Thermal Properties, Electrical Conductivity, and Crystal Structure in the BaCe0.80Y0.20O2.9 Proton Conductor

“…With the progress in the synthesis and characterization of the newly discovered materials, such as the BaCeO 3 and CaZrO 3 perovskites, an intense research has also been devoted to the comprehension of the defect chemistry of the same materials, in order to optimize their performance and build the basis for the development of other solid-state proton conductors [10][11][12][13][14][15] (1) with oxygen vacancies constituting the site for the incorporation of water in the form of hydroxyl groups through:…”