Structural features, nonstoichiometry and high-temperature transport in SrFe1−xMoxO3−δ

Investigation of the microstructural features of SrCo0.8Fe0.2O3−δ perovskite

“…Variation of layer thickness showed that the best correspondence is observed for the thickness of 20 nm for brownmillerite phase and 80 nm for perovskite phase, which agrees with the experimentally determined coherence lengths. Similar nanostructuring phenomena were observed previously for nonstoichiometric ferrites with perovskite structure characterized by oxygen content 2.5<3−δ<2.7 [6][7][8][9]. Because the mobility of oxygen in ferrites is lower by an order of magnitude than that in SrCo 0.8 Fe 0.2 O 3−δ , for systems SrFe 1−x V x O 2.5+x (x00.05, 0.1) [6] and SrFe 1−x Mo x O 2.5 +3/2x (x00.05) [8], as well as SrCo 1−x Al x O 2.5+x [7] and CaTi 0.4 Fe 0.6 O 3−δ [9] the occurrence of nanostructuring in perovskites through the formation of coherent 90°brown-millerite domains randomly disoriented in six directions was (1) with modeling data obtained by the alternation of oxygen-deficient cubic perovskite (S. G. Pm3m) and brownmillerite with space groups Ibm2 (2), Pcmn (3), and Icmm (4).…”

“…For perovskites with oxygen content corresponding to the two-phase region 1/n < δ <1/(n +1) (either in result of redox process or aliovalent doping), as we demonstrated in this work and previously [6,8], nanostructuring, i.e., the formation of nanosized coherently jointed domains having the composition ABO 3−1/n and ABO 3−1/n+1 is characteristic feature. It may be assumed that this process sequentially takes place as the oxygen content of the sample changes, within the whole range of oxygen stoichiometry.…”

“…An intermediate case is nanostructuring, i.e., ordering of oxygen vacancies inside nanosized domains where the defects which are excess with respect to domain structure (oxygen interstitials, vacancies) are ejected to the vicinity of the domain boundaries, where they have higher mobility [4,5]. This phenomenon has been recognized previously as microdomain texture or microtwinning [6][7][8][9]. For materials in which high oxygen transport characteristics are required (oxygen-permeable membranes, electrodes for SOFCs), nanostructuring may play the key role because it is accompanied by the formation of the high concentration of interfaces (domain, antiphase, and twin boundaries) that can be the channels of enhanced diffusion with lower activation barriers [5,10].…”

Oxygen nonstoichiometry, chemical expansion, mixed conductivity, and anodic behavior of Mo-substituted Sr3Fe2O7-δ

“…The incorporation of molybdenum cations can be expected to raise the n-type electronic conduction in moderately reducing atmospheres, as for the perovskite-type analogue [14,15]. This effect, originating from the Mo 5+ formation and from shifting redox equilibrium between iron cations Solid State Ionics 181 (2010) 1052-1063 towards Fe 2+ [14,15], may be of potential interest for the SOFC anodes. At the same time, although donor-type doping is expected to decrease oxygen deficiency, the six-fold oxygen coordination of Mo 6+/5+ might promote vacancy rearrangement between the O1 and O3 sites of Sr 3 (Fe,Mo) 2 O 7-δ lattice, thus providing additional diffusion pathways.…”

Nano-domain states of strontium ferrites SrFe1−MO2.5+ (M=V, Mo; y≤0.1; x≤0.2)

“…Doping of SrFe 1 À y M y O 2.5 þ x with high-charged cations leads to the formation of the system outside the homogeneity region of brownmillerite structure and gives rise to a nano-domain structure [7,8]. The "order-disorder" phase transitions in case of nanostructured oxides do not lead to destruction of the materials.…”