Identification of high ionic conducting members (M(III) = Co, Ni) in the new lithium rich Li 4.50 M 0.50 TeO 6 (M(III) = Co, Ni, In) series

Many new lithium-excess compounds with rock-salt related structures have been extensively studied in recent years to discover high-capacity electrode materials for lithium-ion batteries. In the present work, lithium rich layered tellurates, Li M TeO (M(III) = Co, Ni, In), are added to the existing series of Li M TeO (M(III) = Cr, Mn, Fe, Al, and Ga) oxides. Structural investigations revealed their stabilization in the space group 2/ with a new cationic ordering. The structure consists of (Li M TeO ) honeycomb arrays along the plane by the edge sharing of TeO with (Li/M)O octahedra. The honeycomb arrays are separated by the intermediate layer of Li alone in Li Co TeO . On the other hand, in the Ni and In analogues, the interlayer region consists of Li with Te, and Li with In ions, respectively. XPS studies confirmed the +3 oxidation state of Co and Ni ions. The appearance of a strong band at 680 nm resulting from LMCT (O → Co) in the UV-vis DRS data of the Li Co TeO sample further indicated the presence of Co (d , low spin) ions. The absence of characteristic Ni bands at around ∼650 and 740 nm supported Ni ions. Li Co TeO showed diamagnetic behaviour, while Li Ni TeO displayed paramagnetic nature. A negative (-14(2)) K has been obtained in the temperature region of 300-100 K for Li Ni TeO representing dominant antiferromagnetic interactions. At 2 K, Li Ni TeO unveiled a non-linear trend with no significant hysteresis and nearly saturation at 5 T field indicating the existence of additional interactions. Li Co TeO and Li Ni TeO exhibited significant conductivity values of 0.016 and 0.003 S cm , respectively, at 300 °C, thereby opening up further studies in this direction.