Mechano-Chemical Coupling in Double Perovskites as Energy Related Materials

Abstract

Double perovskites RBaB2O6-δ and Sr2 BMoO6, where R=rare-earth element and B=3d-transition metal, with A-site and B-site, respectively, cation ordering are very promising materials for a variety of different devices for moderate high temperature applications such as solid oxide fuel cells (SOFCs) and mixed ionic and electronic conducting (MIEC) membranes. The unique feature of the oxides is their ability to undergo both thermal strain and that induced by the defects of oxygen nonstoichiometry in the oxide lattice. The latter is called as chemical or defect-induced strain. This property was shown recently to be anisotropic for tetragonal double perovskites unlike that for perovskites with pseudo-cubic structure. The crystal lattice of a double perovskite expands along a-axis and simultaneously contracts along c -axis with the decreasing lattice oxygen content. Expansion along a-axis was found to obey the model for pseudo-cubic oxides proposed by us earlier and based on relative change of mean ionic radius. The possible reasons for lattice contraction along c axis are discussed as well.

Chemical lattice strain in nonstoichiometric oxides: an overview

“…18,144,145 The chemical strain of these oxides, calculated with eqn (32), was shown to agree well with experimentally determined expansion along the a axis, ε chem ( a ). 123,145–147 Moreover, for Sr 2 FeMoO 6– δ , ε chem of the cubic ( Fm 3̄ m ) polymorph is almost equal to that calculated with the model (eqn (32)) as well as to ε chem ( a ) of its tetragonal polymorph. 123,146 This indicates a similar nature of expansion of tetragonal ordered and cubic disordered perovskites along the a axis.…”

“…121,122 In its framework, the isotropic chemical strain of an oxide is approximated by that of a hypothetical crystal lattice formed by close-packed rigid spherical ions. It can be shown (see, for example, Tsvetkov et al 123 ) that the relative linear expansion of either the unit cell or the bulk of such a lattice is equal to the relative change in weighted mean ionic radius:where c i and r i are the concentration and the crystal ionic radius 81 of an i th ion in an oxide, and the subscript 0 denotes the reference state where a = a 0 and L = L 0 .…”

Synthesis, Single Crystal Growth, and Properties of Cobalt Deficient Double Perovskite EuBaCo2−xO6−δ (x = 0–0.1)

“…Interestingly, chemical lattice strain caused solely by oxygen vacancies formation was found to be anisotropic in double perovskites [5,6] with expansion in ab-plane due to decrease of cobalt oxidation state [5,6] and contraction along c-axis due to the high concentration of oxygen vacancies localized in rare-earth-oxygen-(REO-) plane, which prompts shifts in Co and O positions towards the REO-plane [6]. In the case of cobalt deficient double perovskite EuBaCo 2−x O 6− , however, it seems that cobalt oxidation state, and, as a consequence, its mean size (radius), remains unchanged due to cobalt vacancies formation.…”

“…Double perovskites LnBaB 2 O 6− (Ln = rare-earth element, B = 3d element) with layered structure, which consists of alternating perovskite layers containing either rare-earth elements or Ba [1][2][3], have already received great attention in past decades due to their fast oxide ion transport, high mixed ionic and electronic conductivity, and high catalytic activity with respect to the oxygen reduction [2][3][4][5][6]. The double cobaltites LnBabo 2 O 6− are of particular interest due to diverse physical properties of cobalt ions [4,[7][8][9], which may exist not only in different oxidation states: Co 2+ , Co 3+ , and Co 4+ , but also in different spin states, and may have several coordination environments, such as tetrahedral, octahedral, square pyramidal, and trigonal pyramidal.…”

Layered Oxygen-Deficient Double Perovskites as Promising Cathode Materials for Solid Oxide Fuel Cells

“…As can be seen, these values vary within 0.5–2.6%, exhibiting a strong anisotropy; simultaneous chemical expansion along the a -axis (in the ab -plane) and chemical contraction along the c -axis (out-of-plane) take place during the evolution of weakly-bonded oxygen. According to [ 58 , 77 ], the former occurs due to an increase inthe average radii of cobalt ions due to their reduction, but the latter occurs due to the change in the coordination environment of REE and cobalt ions.…”