A brief review of conductivity and thermal expansion of perovskite-related oxides for SOFC cathode

Abstract

Cathode materials with mixed ion-electron conductivity (MIEC) are necessary for the development of low or intermediate temperature solid oxide fuel cells. Perovskite and perovskite-related materials are promising candidates on this role. In the review the conductivity and the thermal expansion of materials with various types of perovskite-related structures such as pure perovskite, double perovskite, brownmillerite and Ruddlesden-Popper phases have been compared. And the literature data on the values of the electronic and ionic conductivities, the oxygen diffusion coefficient, and the thermal expansion coefficient of various compositions have been collected. It was shown that the disordered cubic perovskites possess the higher electronic conductivity whereas the layered perovskites and materials with the Ruddlesden-Popper structure have higher ionic conductivity and lower value of thermal expansion.

Formation of Solid Solutions and Physicochemical Properties of the High-Entropy Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (Ln = La, Pr, Nd, Sm or Gd) Perovskites

“…The thermomechanical behavior within the Ln(Co,Cr,Fe,Mn,Ni)O 3−δ series is similar for all compositions, although the correlation between the ionic radius of lanthanide ion and the value of TEC occurs-in general, the smaller the radius, the lower is the thermal expansion coefficient, which is especially evident for the La-based composition (Table 3). Such behavior is in line with that typically reported for the conventional LnTMO 3 perovskites [29], as well as other perovskite-type structures [35]. No sign of chemical expansion due to the oxygen release from the structure (i.e., increase of TEC) can be observed at higher temperatures, indicating that the materials maintain their total oxygen content up to 900 • C without any significant decrease.…”

“…The possibility of such modifications of the LnTMO 3 high-entropy perovskites has already been successfully proven in [22]. Still, the selection of the A-site lanthanide is expected to play an equally important role concerning the overall properties of the system, directly influencing electronic and ionic conductivity [19], thermomechanical and magnetic properties [20,29], but also indirectly affecting the system through different available alkaline-earth dopant solubility limit [30]. The present study aims to evaluate the lanthanide selection on the structure and properties of base Ln(Co,Cr,Fe,Mn,Ni)O 3−δ perovskites, as well as on the influence of Ln on the solubility of the most typical A-site dopant-Sr.…”

Ruddlesden-Popper phase A2BO4 oxides: Recent studies on structure, electrical, dielectric, and optical properties

“…CoO (LSC) perovskite. Most of the undoped A BO layered perovskites are poor oxide ion conductor due to less oxygen vacancies and interstitial oxide ions [80]. As discussed in Section 2, on partial substitution the oxygen stoichiometry tunes, i.e., material either becomes hypo-stoichiometric or hyper-stoichiometric [39,81].…”

Perovskite Structure Associated with Precious Metals: Influence on Heterogenous Catalytic Process

“…The electronic structure in perovskite oxides is defined by a lattice of BO 6 octahedra clusters, whereby their B-O-B bonds build up an electrical conduce way along the crystal structure through which the electrons and/or holes "flow" [43,45,55]. The lattice distortion degree of the pristine ABO 3 induced by ion doping may induce structural defects on the crystal structure generating and/or rearranging energy state levels that change the electronic structure strongly.…”

“…Thus, the same precious-doped perovskite matrix may suffer different distortion degrees according to the kind of precious metal present in its structure. Thereby, the lattice distortion may change the electronic structure of perovskite oxide materials remarkably and consequently affect the carrier transport mechanisms [39,44,47,48,55]. On the plasmonic point of view, the decision on the noble metals to be used should consider those able to support a strong surface plasmon resonance effect at the desired resonance wavelength.…”