Microstructure of mayenite 12CaO·7Al 2 O 3 and electron emission characteristics

Electron emission characteristic, electrical conductivity of polycrystalline mayenite (12CaO·7Al 2 O 3 ) electride, formation of [Ca 24 Al 28 O 64 ] 4+ (e − ) 4 framework as a function of phase content, and microstructure have been investigated. The mayenite microstructure was investigated using high‐resolution transmission microscopy which revealed the type cage structure of 12CaO·7Al 2 O 3 partially filled by extra‐framework oxygen ions. Incorporation of electrons by means of carbon C 2 2 ‐ion template 12CaO·7Al 2 O 3 produces complex structure, and an incomplete C 2 2 ‐ion template 12CaO·7Al 2 O 3  structure consisting of mixture of a [Ca 24 Al 28 O 64 ] 4+ (e − ) 4 and [Ca 24 Al 28 O 64 ] 4+ (O 2− ) 2 framework had a direct effect on the electron emission. Surface chemistry and stability of the 12CaO·7Al 2 O 3 electride have been studied using x‐ray photoelectron spectroscopy. The work function of phase pure 12CaO·7Al 2 O 3 electride was determined from direct thermionic emission data and compared to the measurement from ultraviolet photoelectron spectroscopy (UPS). Depending on the extent of C 2 2 ‐ion template of 12CaO·7Al 2 O 3  structure, a work function of 0.9–1.2 eV and 2.1–2.4 eV has been measured and thermionic emission initiating at 600°C.