Enhancing the injected electron concentration and thermionic emission property in C12A7:e − ceramic via Al site Zr doping

Abstract [Ca 24 Al 28 O 64 ] 4+ (4e − ) (C12A7:e − ) has excellent potential in electric propulsion owing to various advantages, including low work function, low working temperature, and stable chemical properties. However, increasing electron concentration enhances the thermionic emission property of C12A7:e − . This study used a chemical method—spark plasma sintering to synthesize Zr‐doped C12A7:e − (C12(A 1 − x Z x )7:e − , where x = 0 to 0.14). The study results show that C12(Al 0.86 Zr 0.14 )7:e − maximum injected electron concentration ( n ), conductivity ( σ ), electron mobility ( μ n ), and zero‐field emission current density ( J o ) improved to 2.4 × 10 21 /cm 3 , 1507 S/cm, 5.2 cm 2 /V·s, and 2.4 A/cm 2 , respectively. The emission current density of the C12(Al 0.86 Zr 0.14 )7:e − could be maintained at about 2.9 A/cm 2 under 1100°C, 4000 V, and 600 min. Theoretical calculation results prove that Zr doping broadens the cage conduction band (CCB) of C12A7:e − and reduces the bandgap between the CCB and the frame conduction band. In addition, Zr doping increases the electronic density of states near the Fermi level, and the density of states presents a continuous state. This helps to increase the injected electron concentration and enhance the electrical transport and thermionic emission characteristics of the sample. The calculation results provide theoretical support for the experiment.