Cs 0.9 Ni 3.1 Se 3 : 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: Cs0.9 Ni3.1 Se3 . This compound adopts the TlFe3 Te3 -type structure with space group P63 / m, which consists of infinite [Ni3 Se3 ] 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 Cs0.9 Ni3.1 Se3 is nonstoichiometric, which is different from the other TlFe3 Te3 -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. Cs0.9 Ni3.1 Se3 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.