Superconductivity in Sr(Pd_1-xNi_x)₂Ge ₂

The systematic variations of lattice structure and superconducting transition temperature in Sr(Pd_1-xNi_x)₂Ge ₂ are reported. The X-ray diffraction patterns can be labeled by tetragonal I4/mmm (no. 139) space group with only minor impurities, which indicates the substitution Ni into Pd sites is successful and formed pure phase. The tetragonal lattice parameter a decreases and c increases monotonically with Ni concentration x, while the unit cell volume decreases. A systematic, gradual change of superconducting transition temperature T_c increases slightly to 3.2 K for very small Ni doping of x ∼ 0.1 then slowly decreases to 2.1 K for x = 0.5. Further investigation for SrNi₂Ge₂ by low temperature resistivity indicated a T_c,mid of 0.87 K suggesting that superconductivity exists through the whole Ni substitution levels.