Structure and anisotropic properties of BaFe2-xNixAs2 (x=0, 1, and 2) single crystals

The crystal structure, electrical resistivity, magnetic susceptibility, and heat capacity of single crystals of BaFe2As2, BaNi2As2, and BaFeNiAs2 are reported. BaFe2As2 data indicate the equivalence of C(T), d(chi T)/dT, and d rho/dT results in determining the antiferromagnetic transition at T-N=132(1)K. BaNi2As2 shows a structural phase transition from a high-temperature tetragonal phase to a low-temperature triclinic phase (P1 symmetry) at T-0=131 K, with superconducting critical temperature T-c=0.69 K. BaFeNiAs2 does not show any sign of superconductivity and its properties resemble BaCo2As2, a renormalized paramagnetic metal.