Thermal conductivity and Seebeck coefficient of 12CaO7 Al2 O3 electride with a cage structure

Thermal conductivity (κ) and Seebeck coefficient (α) of electron-doped light-metal oxide 12CaO7 Al2 O3 (C12A7 electride) with a subnanometer-sized cage structure are reported on single crystals with various electron concentrations (Ne). The semiconducting C12A7 electride exhibits n -type conduction with the highest α value of -100 μV K-1 at 300 K. The κ exhibits an amorphouslike T2 dependence at low temperatures and varies between 2.3 and 4.5 Wm-1 K-1 at 300 K. This is an order-of-magnitude lower than that of the constituents, CaO (15 Wm-1 K-1) and Al2 O3 (30 Wm-1 K-1). These properties are attributed to the cage structure, suggesting that the semiconducting electride should be regarded as a phonon glass and electron crystal material. The thermoelectric performance of electrides evaluated by a dimensionless figure of merit (ZT) shows an optimized value of 2× 10-3 at 300 K for the semiconducting electride with Ne of 5× 1020 cm-3.