Floating Zone Growth and Characterization of (Ca_1- Nd )₁₂Al₁₄O₃₃₊₆ (x ∼ 0.001) Single Crystals

Rare earth Nd³⁺ ion-doped Ca₁₂Al₁₄O₃₃ 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 mm³ 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 × 10²¹ and ∼1.8 ± 0.1 × 10²¹ 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.