One of the greatest challenges in the enhancement of the electrical properties of conductive mayenite [CaAlO](4e) (hereinafter C12A7:e) is the design of a more suitable/simple synthesis strategy that can be employed to obtain the required properties such as excellent stable electrical conductivity, a high electron concentration, outstanding mobility, and an exceptionally large surface area. Therefore, to synthesize C12A7:e in the metallic state, we proposed a facile, direct synthesis strategy based on an optimized sol-gel combustion method under a nitrogen gas environment using the low-cost precursors Ca(NO)·4HO and Al(NO)·9HO. Using this developed strategy, we successfully synthesized moderately conductive nanoscale C12A7:e powder, but with unexpected carbon components (reduced graphene oxide (rGO) and/or graphene oxide (GO)). The synthesized C12A7:e composite at room temperature has an electrical conductivity of about 21 S cm, a high electron concentration of approximately 1.5 × 10 cm, and a maximum specific surface area of 265 m g. Probably, the synthesized rGO was coated on nanocage C12A7:e particles. In general, the C12A7:e electride is sensitive to the environment (especially to oxygen and moisture) and protected by an rGO coating on C12A7:e particles, which also enhances the mobility and keeps the conductivity of C12A7:e electride stable over a long period. Doped mayenite electride exhibits a conductivity that is strongly dependent on the substitution level. The conductivity of gallium-doped mayenite electride increases with the doping level and has a maximum value of 270 S cm, which for the first time has been reported for the stable C12A7:e electride. In the case of Si-substituted calcium aluminate, the conductivity has a maximum value of 222 S cm at room temperature.
A facile method to prepare pristine nanoscale mayenite electride is presented. The highest achieved conductivity of melted sample was ~28 S cm−1, with 93% mass density.
Novel approaches to synthesize efficient inorganic electride [Ca24Al28O64]4+(e−)4 (thereafter, C12A7:e−) at ambient pressure under nitrogen atmosphere, are actively sought out to reduce the cost of massive formation of nanosized powder as well as compact large size target production. It led to a new era in low cost industrial applications of this abundant material as Transparent Conducting Oxides (TCOs) and as a catalyst. Therefore, the present study about C12A7:e− electride is directed towards challenges of cation doping in C12A7:e− to enhance the conductivity and form target to deposit thin film. Our investigation for cation doping on structural and electrical properties of Sn- and Si-doped C12A7:e− (Si-C12A7:e, and Sn-C12A7:e−) reduced graphene oxide (rGO) composite shows the maximum achieved conductivities of 5.79 S·cm−1 and 1.75 S·cm−1 respectively. On the other hand when both samples melted, then rGO free Sn-C12A7:e− and Si-C12A7:e− were obtained, with conductivities ~280 S.cm−1 and 300 S·cm−1, respectively. Iodometry based measured electron concentration of rGO free Sn-C12A7:e− and Si-C12A7:e−, 3 inch electride targets were ~2.22 × 1021 cm−3, with relative 97 ± 0.5% density, and ~2.23 × 1021 cm−3 with relative 99 ± 0.5% density, respectively. Theoretical conductivity was already reported excluding any associated experimental support. Hence the above results manifested feasibility of this sol-gel method for different elements doping to further boost up the electrical properties.
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