1. “Crystal structures of superconducting sodium intercalates of hafnium nitride chloride”. Oró-Solé J, Frontera C, Beltrán-Porter D, Lebedev OI, Van Tendeloo G, Fuertes A, Materials research bulletin 41, 934 (2006).   http://doi.org/10.1016/j.materresbull.2006.03.018