Floating Zone Growth and Characterization of (Ca_1–xNd_x)₁₂Al₁₄O_33+6x (x ～ 0.001) Single Crystals

摘要

Rare earth Nd~(3+) ion-doped Ca_(12)Al_(14)O_(33) single crystals were grown at a rate of 1 mm/h by the floating zone technique in an oxygen atmosphere. The Nd concentration in the central area of the as-grown crystals was higher than that in the peripheral area due to the highly concave growth interface shape. The average Nd concentration in the as-prepared parallelepiped slices of ～6 × 3 × 2 mm~(3) for electride fabrication was ～0.093 ± 0.011 atom % Nd in contrast to the nominal 0.1 atom % Nd concentration. The Nd-doped C12A7:Nd single crystalline electride prepared by thermal treatment with a Ti metal at 1100 °C for 48 h induced an insulator–metal transition with the highest conductivity of approximately 1165 S/cm. These annealing conditions provide an approach to completely remove clathrated oxide ions from the crystallographic cages, leading to the formation of C12A7:Nd(e ~(–)) and C12A7:e ~(–) electrides with high-density electrons (～2.4 ± 0.2 × 10~(21) and ～1.8 ± 0.1 × 10~(21) cm~(–3)) localized in the cages. The carrier mobility at room temperature in C12A7:Nd(e ~(–)) was very similar to that in C12A7:e ~(–), even though it was very high at temperatures below ～150 K.