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

Abstract

Inspired by the successful synthesis of alkaline-earth-metals-based electrides [Ca 24 Al 28 O 64 ] 4+ (e – ) 4 (C12A7:e – ) and [Ca 2 N] +: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: Sr 5 P 3, Sr 8 P 5, Sr 3 P 2 and Sr 4 P 3 . Of these structures, we identify Sr 5 P 3 and Sr 8 P 5 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 Sr 5 P 3 and the experimental confirmation of its structure. Although density functional calculations with the generalized gradient approximation predict Sr 5 P 3 to be a metal, electrical conductivity measurement reveal semiconducting properties characterized by a distinct band gap, which indicates that the newly synthesized Sr 5 P 3 is an ideal one-dimensional electride with the half-filled band by unpaired electrons. In addition to presenting the novel electride Sr 5 P 3, 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.