Analysis of structural and electronic properties of Pr ₂NiO ₄ through first-principles calculations

The structural and electronic properties of bulk Pr ₂NiO _4+δ (δ=0 and 0.031) were analyzed using first-principles calculations based on the density functional theory (DFT) for application to electrode materials in solid-oxide fuel cells (SOFCs). Two structures of Pr ₂NiO ₄ were analyzed: one in space group I4/mmm associated with the high temperature tetragonal (HTT) structure, and the other in Bmab with the low temperature orthorhombic (LTO) structure. The main difference between the two structures is the pronounced tilting of the nickelate octahedra found in the Bmab structure. Here, we will show that the difference in the electronic properties between the two structures, i.e.half-metallic for the I4/mmm structure and metallic for the Bmab structure, is attributed to the tilting of the nickelate octahedra. Furthermore, we found that the presence of interstitial O atoms at the Pr ₂O ₂ bilayers is responsible for the tilting of the octahedra and thus is a dominant factor in the transition from the I4/mmm structure to the Bmab structure. These results would be of great significance to materials design related to the enhancement of O diffusivity in this material.