Exploration of Stable Strontium Phosphide-Based Electrides: Theoretical Structure Prediction and Experimental Validation

Inspired by the successful synthesis of alkaline-earth-metals-based electrides [Ca₂₄Al₂₈O₆₄]⁴⁺(e^-)₄ (C12A7:e^-) and [Ca₂N]⁺:e^- and high-throughput database screening results, we explore the potential for new electrides to emerge in the Sr-P system through a research approach combining ab initio evolutionary structure searches and experimental validation. Through employing an extensive evolutionary structure search and first-principles calculations, we first predict the new structures of a series of strontium phosphides: Sr₅P₃, Sr₈P₅, Sr₃P₂ and Sr₄P₃. Of these structures, we identify Sr₅P₃ and Sr₈P₅ as being potential electrides with quasi-one-dimensional (1D) and zero-dimensional (0D) character, respectively. Following these theoretical results, we present the successful synthesis of the new compound Sr₅P₃ and the experimental confirmation of its structure. Although density functional calculations with the generalized gradient approximation predict Sr₅P₃ to be a metal, electrical conductivity measurement reveal semiconducting properties characterized by a distinct band gap, which indicates that the newly synthesized Sr₅P₃ is an ideal one-dimensional electride with the half-filled band by unpaired electrons. In addition to presenting the novel electride Sr₅P₃, we discuss the implications of its semiconducting nature for 1D electrides in general and propose a mechanism for the formation of electrides with an orbital level diagram based on first-principles calculations.