High-Density Electron Anions in a Nanoporous Single Crystal: [Ca 24 Al 28 O 64 ] 4 + (4 e - )

Abstract

We removed ∼100% of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO·7Al ₂ O ₃ , leading to the formation of high-density (∼2 × 10 ²¹ cm ^{– 3} ) electrons highly localized in the cages. The resulting electron forms a structure that we interpret as an F ⁺ center and migrates throughout the crystal by hopping to a neighboring cage with conductivity ∼100 siemens per centimeter, demonstrating that the encaged electron behaves as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The resulting [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} (4 e ^– ) may be regarded as a thermally and chemically stable single crystalline “electride.”