Yuan, H. Q., Grosche, F. M., Carrillo-Cabrera, W., Paschen, S., Langhammer, C., Sparn, G., Baenitz, M., Grin, Y., & Steglich, F. (2002). The Novel Superconducting Clathrates: Ba6Ge25 and Na2Ba4Ge25. AIP Conference Proceedings, 629, 233-241. doi:10.1063/1.1509149.