Superconducting nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I)

Christian M. Schurz, Larysa Shlyk, Thomas Schleid, Rainer Niewa
2011 Zeitschrift für Kristallographie  
Two different polymorphs of the metal nitride halides MNX (M ¼ Ti, Zr, Hf; X ¼ Cl, Br, I) are known to crystallize in layered structures. The two crystal structures differ in the way 2 1 {X[M 2 N 2 ]X} slabs are stacked along the c-axes. Metal atoms and/or organic molecules can be intercalated into the van-der-Waals gap between these layers. After such an electron-doping via intercalation the prototypic band insulators change into superconductors with moderate high critical temperatures T c up
more » ... emperatures T c up to 25.5 K. This review gathers information on synthesis routes, structural characteristics and properties of the prototypic nitride halides and the derivatives after electron-doping with a focus on superconductivity. 2. Synthesis of the starting materials MNX (M ¼ Ti, Zr, Hf; X ¼ Cl, Br, I) Synthesis via ammonolysis After Ruff and Eisner [11] investigated the Ti/N/Cl(Br) system to clarify compositions of different earlier formulated titanium nitrides in 1908, the already well known ammonolysis technique [12, 13] became a popular synthesis method for group IV nitride halides. Following the confirmation of the existence of TiNBr and TiNI by Fowles and Nicholls in 1958 [14], Juza and co-workers prepared various pure titanium and zirconium nitride halides during the 1960s [3, 4, 15, 16]. For synthesis the tetra- Z. Kristallogr. 226 (2011) 395-416 /
doi:10.1524/zkri.2011.1350 fatcat:ssv7meqjlrbbdcxorkjjgaoiya