Structure and physical properties of Ni-based quasi-one-dimensional selenides Rb_0.9Ni_3.1Se₃ and K_0.7Ni_3.1Se₃

The materials with quasi-one-dimensional crystal structure have gained intense interest because of their novel structure and related properties such as electron correlations, charge-density wave and potential superconductivity. Here we report two new Ni-based quasi-one-dimensional selenides: Rb_0.9Ni_3.1Se₃ and K_0.7Ni_3.1Se₃. These two compounds are nonstoichiometric and composed of one-dimensional (Ni₃Se₃)_∞ infinite chains with face-sharing Ni₆ octahedra along the c direction. It is found that the interchain distance in these compounds is strongly influenced by the radius of intercalated alkali-metal cations, while the configuration of (Ni₃Se₃)_∞ chains is basically unaffected. The conductivity measurement indicates the metallic behavior of Rb_0.9Ni_3.1Se₃ and K_0.7Ni_3.1Se₃. Meanwhile, the magnetic susceptibility reveals the spin-glass state below 10 K. It is indicated that the magnetic moments in these compounds are related to the Ni[sbnd]Ni bonding distance. First-principles calculation reproduces the metallic state of this 133 phase, and also suggests that the magnetic interaction is attributed to the extra Ni in structure. These compounds form a Ni-based quasi-one-dimensional material family, which provides new platform to understand the structure-property relationship of quasi-one-dimensional materials, and also offer a series of potential precursors to synthesis the novel (Ni₃Se₃)_∞ molecular wires.