Oxygen Non-Stoichiometry and Point Defect Equilibria in (La_1/6Pr_1/6Nd_1/6Gd_1/6Ba_1/6Sr_1/6)MnO_{3- δ}

Compositionally complex oxides (CCOs), also referred to as high entropy oxides, have several different cations (typically 5 or more) occupying a single site. CCOs have shown unique dielectric, ionic conductivity, and thermal conductivity properties, in addition to promising electrochemical properties for solid oxide fuel cells (SOFCs) [1,2]. In this work, the A-site of the common SOFC cathode La 0.8 Sr 0.2 MnO 3-δ (LSM) is modified with additional lanthanide and alkali elements, resulting in the composition (La 1/6 Pr 1/6 Nd 1/6 Gd 1/6 Ba 1/6 Sr 1/6 )MnO 3- δ . Typically, the average lattice parameter is correlated with bond length and strength, and thus energetics of oxygen vacancy formation energy. In the compositionally complex system, there is a wide range of cation radii on the A-site and so bond strengths are expected to vary significantly, resulting in a distribution of oxygen vacancy formation energies. Initial results have shown that the amount of oxygen released during reduction is significantly greater for the studied CCO in comparison with La 2/3 Sr 1/3 MnO 3-δ , the latter having the same amount of total acceptor dopant and with a similar lattice parameter as the CCO. The significant enhancement in oxygen loss is an indicator of a lower reduction enthalpy and suggests a significant impact from atomic structure that is not captured in long-range structure parameters (i.e., average lattice parameter). The oxygen non-stoichiometry measured by thermogravimetric analysis in ~10 -5 – 1 atm O 2 at 1200 o C – 1450 o C will be presented and the point defect equilibria analysis will be discussed. Comparisons with existing high temperature experimental and modeling studies on LSM will also be discussed. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 References [1] Xu, Y., et al., J. Adv. Ceram., 11 (2022) 794, DOI:10.1007/s40145-022-0573-7 [2] J. Dabrowa, et al., J. Mater. Chem. A, 8 (2020) 24455; DOI:10.1007/s40145-022-0573-7