Unraveling Crystal Structure and Transport Properties of Fast Ion Conducting SrCo_0.9Nb_0.1O_3−δ

Abstract

SrCo0.9Nb0.1O3−δ (SCN) has been investigated for oxygen transport membrane and solid oxide fuel cell applications as it is more stable than the state-of-the-art Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) material. Here, the crystal structure and transport properties of SCN were systematically investigated. Combined neutron and high-temperature X-ray powder diffraction analyses over the temperature range of 25–800 °C showed that the crystal structure of SCN belongs to the tetragonal space group P4/mmm with the unit cell a c × a c × 2a c, where a c is the lattice parameter of the cubic perovskite at temperatures <160 °C. The tetragonal (P4/mmm) to cubic (Pm3̅m) phase transition occurred in SCN with increasing temperature. This phase transition affected the electrical conductivity, whereas the impact on the magnetic susceptibility was not significant. The surface exchange and diffusion coefficients of SCN in the temperature range of 600–850 °C were characterized by electrical conductivity relaxation and oxygen permeation measurements. The self-diffusion and surface exchange coefficient of SCN are comparable with those of BSCF. Hence, SCN shows promise as a next-generation mixed ionic–electronic conducting ceramic.

Effects of Nb and Sn co-doping on the structure and properties of SrCoO3-δ oxygen transport membranes

“…Figure 1(a) shows the XRD patterns of the synthesized SCN, SCNT3, and SCNT5 powders, which confirmed the formation of perovskite-type oxide phases. The obtained XRD patterns are typical for perovskite-type oxide phases reported in the literature [23][24][25]27,28,30]. No evidence of secondary phases was observed, thus indicating that both Nb and Sn are incorporated into the perovskite lattice.…”

“…Figure 2 illustrates the observed, calculated, and difference profiles of SCNT3 and SCNT5 from the Rietveld refinement. Both SCNT3 and SCNT5 crystallized in the tetragonal space group P4/mmm, which is isostructural to SCN [30]. As shown in Figure 2(b,e), the characteristic (1 0 5) (2 1 3) and (1 1 5) (2 2 1) peaks at~79°and~85°c onfirm the formation of tetragonal perovskite because these peaks are absent in the cubic perovskite.…”

“…Many literature sources report a conventional cubic perovskite structure (space group Pm 3m and a~3.8 Å) for SCN [23][24][25]27,28], however, the crystal structure obtained from the neutron diffraction study of SCN exhibited a tetragonal perovskite structure (space group P4/mmm, a~3.8 Å and c = 7.6 Å) [30]. The crystal structures of SCNT3 and SCNT5 were investigated further by employing the Rietveld refinement to analyze the neutron diffraction patterns at 25°C.…”

“…B-site cations play a crucial role for both phase stability and oxygen transport properties [21]. It was found that 10 mol% Nb-doped SrCoO 3-δ (i.e., SrCo 0.9 Nb 0.1 O 3-δ ) shows promising oxygen permeability and low area specific resistance comparable to that of the Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ stabilizing oxygen vacancydisordered perovskite structure at operational conditions [22][23][24][25][26][27][28][29][30]. Similarly, Sn has been recognized as an effective B-site dopant for stabilizing oxygen vacancydisordered structures.…”

“…To the best of our knowledge, this is the first study on the effect of small amounts of Sn-doping on SrCo 0.9 Nb 0.1 O 3-δbased oxygen transport membranes. [30], where stoichiometric amounts of the precursors, SrCO 3 (Sigma Aldrich, ≥ 99.9 %), Co 3 O 4 (Alfa Aesar, ≥ 99%), Nb 2 O 5 (Sigma Aldrich, ≥ 99.9 %), and SnO 2 (Sigma Aldrich, ≥ 99.9%), were processed by ball milling in ethanol for 48 h. Then, the powders were calcined at 1100°C for 5 h in air, followed by uniaxial pressing at 100 MPa and isostatic pressing at 400 MPa to form green disks. The discs were sintered at 1200°C for 5 h in air.…”