Identification of high ionic conducting members (M() = Co, Ni) in the new lithium rich LiMTeO (M() = 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 4.50 M 0.50 TeO 6 (M( iii ) = Co, Ni, In), are added to the existing series of Li 4.50 M 0.50 TeO 6 (M( iii ) = Cr, Mn, Fe, Al, and Ga) oxides. Structural investigations revealed their stabilization in the space group C 2/ m with a new cationic ordering. The structure consists of (Li 1.50 M 0.50 TeO 6 ) 3− honeycomb arrays along the ab plane by the edge sharing of TeO 6 with (Li/M)O 6 octahedra. The honeycomb arrays are separated by the intermediate layer of Li alone in Li 4.50 Co 0.50 TeO 6 . 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 4.50 Co 0.50 TeO 6 sample further indicated the presence of Co 3+ (d 6 , low spin) ions. The absence of characteristic Ni 2+ bands at around ∼650 and 740 nm supported Ni 3+ ions. Li 4.50 Co 0.50 TeO 6 showed diamagnetic behaviour, while Li 4.50 Ni 0.50 TeO 6 displayed paramagnetic nature. A negative (−14(2)) K has been obtained in the temperature region of 300-100 K for Li 4.50 Ni 0.50 TeO 6 representing dominant antiferromagnetic interactions. At 2 K, Li 4.50 Ni 0.50 TeO 6 unveiled a non-linear trend with no significant hysteresis and nearly saturation at 5 T field indicating the existence of additional interactions. Li 4.50 Co 0.50 TeO 6 and Li 4.50 Ni 0.50 TeO 6 exhibited significant conductivity values of 0.016 and 0.003 S cm −1 , respectively, at 300 °C, thereby opening up further studies in this direction. A new series of lithium-rich oxides, Li 4.50 M 0.50 TeO 6 (M = Co, Ni, In), has been investigated for the structural, optical and magnetic properties. The ionic conductivity measurements reveal remarkable values for the Co and Ni analogues.