Evidence for Bardeen-Cooper-Schrieffer-type superconducting behavior in the electride (CaO)12(Al2O3)7 :: e- from heat capacity measurements

The heat capacity of the single crystalline electride of ( CaO)(12) (Al2O3)(7) : e(-) (C12A7: e(-)) with T-c= 0.2 K was larger than that of electron- undoped C12A7 in the temperature range 0.085 - 5 K, reflecting the metallic nature of the electride. A superconducting transition was detected as a heat capacity jump Delta C-p= 3.4 mJ mol(-1) K-1, and the profile and magnitude of Delta C-p agreed well with those expected from the BCS theory. The electronphonon coupling constant ( lambda similar to 0.46 ) and Debye temperature ( Theta(D) similar to 630 K ) were much larger than those for alkali metals having s- like conduction electrons as in the present electride, suggesting that electrides having a rigid structure will be a class of BCS superconductors.