Influence of atomic configuration on electronic and magnetic properties of complex Ruddlesden-Popper oxides La2−xSrxCo1/2Fe1/2O4

Ruddlesden-Popper (RP) transition-metal oxides belong to a versatile class of functional materials whose electronic properties can be tuned by varying chemical composition in a wide range. However, the relation between chemical composition and electronic properties of multi-metal RP oxides, in particular taking into account different distributions of metal ions in the lattice, has not been investigated systematically so far. In this work, we use density-functional theory (DFT) to explore the compositional dependence of electronic, magnetic, and structural properties of La <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts><mml:mrow><mml:mn>2</mml:mn> <mml:mo>-</mml:mo> <mml:mi>x</mml:mi></mml:mrow> </mml:mmultiscripts> </mml:math> Sr <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>x</mml:mi></mml:mmultiscripts> </mml:math> Co <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts><mml:mrow><mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn></mml:mrow> </mml:mmultiscripts> </mml:math> Fe <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts><mml:mrow><mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn></mml:mrow> </mml:mmultiscripts> </mml:math> O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mn>4</mml:mn></mml:mmultiscripts> </mml:math> oxide series for x = 0, 1, 2. To account for localized nature of transition-metal d-orbitals, self-consistent DFT+U approach Agapito-Curtarolo-Buongiorno-Nardelli (ACBN0) is employed. We show that widely used electronic-structure-based descriptors of oxygen-defect formation energies, oxygen transport, and catalytic activity strongly depend on the distribution of transition metal ions. Nevertheless, the distribution-averaged and ground-state descriptor values for La <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts><mml:mrow><mml:mn>2</mml:mn> <mml:mo>-</mml:mo> <mml:mi>x</mml:mi></mml:mrow> </mml:mmultiscripts> </mml:math> Sr <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>x</mml:mi></mml:mmultiscripts> </mml:math> Co <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts><mml:mrow><mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn></mml:mrow> </mml:mmultiscripts> </mml:math> Fe <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts><mml:mrow><mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn></mml:mrow> </mml:mmultiscripts> </mml:math> O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mn>4</mml:mn></mml:mmultiscripts> </mml:math> are found to depend monotonically on the composition x. In addition, we showed that in complex systems such as multi-metal Ruddlesden-Popper phases, Hubbard U values for the same species vary significantly between crystallographically non-equivalent sites.