Cs_0.9Ni_3.1Se₃: A Ni-Based Quasi-One-Dimensional Conductor with Spin-Glass Behavior

In this work, we report the discovery of a new Ni-based quasi-one-dimensional selenide: Cs_0.9Ni_3.1Se₃. This compound adopts the TlFe₃Te₃-type structure with space group P6₃/ m, which consists of infinite [Ni₃Se₃] chains with face-sharing Ni₆ octahedra along the c direction. The lattice parameters are calculated as a = 9.26301(4) Å and c = 4.34272(2) Å, with the Ni-Ni distance in the ab plane as 2.582(3) Å, suggesting the formation of a Ni-Ni metallic bond in this compound. Interestingly, it has been found that Cs_0.9Ni_3.1Se₃ is nonstoichiometric, which is different from the other TlFe₃Te₃-type phases reported so far. Structure refinement shows that the extra Ni atom in the structure may occupy the 2c site, together with Cs atoms. Cs_0.9Ni_3.1Se₃ shows metallic behavior with monotonously decreased resistivity with temperatures from 300 to 0.5 K. Measurements on the magnetic susceptibility display a spin-glass state below 7 K. The specific heat curve gives a Sommerfeld coefficient of 14.6 mJ·K^-2·mol^-1 and a Debye temperature of 143.6 K. The discovery of this new compound enriches the diversity of low-dimensional materials in a transition-metal-based family and also sheds light on the structure-property relationship of this system.