“…The nickel-based pnictides SrNi 2 P 2 , SrNi 2 As 2 , BaNi 2 P 2 , and BaNi 2 As 2 have recently been found to be superconducting ( T c = 1.4, 0.62, 2.5–3, , and 0.7 K, respectively), along with the chalcogenides KNi 2 S 2 and KNi 2 Se 2 ( T c = 0.5 and 0.8 K, respectively) and the germanide SrNi 2 Ge 2 ( T c = 0.87 K) . Partial substitution at the p-block element or transition-metal site causes an increase of the critical temperature. , For example, the solid solutions BaNi 2 P 2– x Ge x and SrNi 2 P 2– x Ge x show an increase of T c up to 2.9 and 3.0 K, respectively, upon substitution of P atoms by Ge atoms, which can be regarded as a direct hole doping of the superconducting [Ni 2 P 2 ] layers. , …”