Synthesis, Characterization, and Electronic Properties of Nickel-Based Pnictides Th 2 Ni 5 As 3 N 2

We report the synthesis, structure, and physical properties of a novel quaternary compound, Th 2 Ni 5 As 3 N 2 . The target compound crystallizes in a tetragonal structure with lattice parameters a = 4.0650(4) Å and c = 22.0728(5) Å at 300 K. Its structure can be described as alternating stacking of antifluorite-type double-layered [Ni 5 As 3 ] subunits and fluorite-type [Th 2 N 2 ] layers along the c axis. The reduced axial ratio of the compound is attributed to the built-in chemical pressure exerted by the [Th 2 N 2 ] layers. A structural phase transition, accompanied by a resistivity anomaly and a specific heat jump, was observed at around 280 K. No superconductivity was detected down to 0.4 K. Electrical resistivity, heat capacity, magnetic susceptibility measurements, and first-principles calculations suggest metallic behavior with Pauli paramagnetism. Drawing from both experimental data and band calculations, the structural transition in relation to chemical pressure and the [Ni 5 As 3 ] subunit is discussed.