Synthesis, Reduction, and Electrical Properties of Macroporous Monolithic Mayenite Electrides with High Porosity

Room-temperature stable macroporous mayenite electride (C12A7:e^-) has been successfully prepared via a sol-gel method accompanied by phase separation, followed by heat-treatment and reduction processes. The obtained xerogel monoliths possess controllable macrostructure and a porosity of more than 60%, depending on adjusting the amount of poly(ethylene oxide) as a phase separation inducer. Heat-treatment allows the formation of multicrystals Ca₁₂Al₁₄O₃₂Cl₂ and Ca₁₂Al₁₄O₃₃ (C12A7), and the porosity increases to 78.67% after being heat-treated at 1100 °C. Further reduction promotes the transformation from Ca₁₂Al₁₄O₃₂Cl₂ or C12A7 to C12A7:e^- as well as the conversion from an insulator to a semiconductive electride. The carrier concentration of the electride reaches 3.029 × 10¹⁸ cm^-3 after being reduced at 1100 °C under Ar atmosphere, and the porosity still remains 66%. The macrostructure of the resultant mayenite electride before and after heat-treatment and reduction is perfectly preserved, indicating that the obtained macroporous monolithic mayenite electride could be utilized in the electronic components.