Formation of honeycomb ordered monoclinic Li2M2TeO6 (M = Cu, Ni) and disordered orthorhombic Li2Ni2TeO6 oxides

Abstract

Ion-exchange reactions of Na2Cu2TeO6 with excess of lithium nitrate at low temperature (300 °C) readily resulted in an isostructural honeycomb ordered monoclinic layered structure Li2Cu2TeO6, otherwise inaccessible by direct solid state high temperature reactions. Similarly, Li2Ni2TeO6(I) stabilized approximately in equal amounts in both of the known P2-type polymorphs (P6(3)/mcm and P6(3)22) was synthesized as an ion-exchange reaction product from Na2Ni2TeO6 using a melt of lithium nitrate. Additionally, a unique tellurium containing oxide Li2Ni2TeO6(II) without the honeycomb ordering of Ni(2+)/Te(6+) ions has been obtained for the first time by the direct high temperature (800-900 °C) synthesis. The oxides were investigated by refinement of powder X-ray diffraction patterns, room temperature magnetization experiments along with Raman spectroscopy and photoluminescence measurements. A structural model has been suggested for the metastable Li2Ni2TeO6(II) and the presence of structural disorder was evidenced in the broadening of the Raman bands and the intense broad photoluminescence (PL) spectra obtained for Li2Ni2TeO6(II).

Li3Co1.06(1)TeO6: synthesis, single-crystal structure and physical properties of a new tellurate compound with CoII/CoIIImixed valence and orthogonally oriented Li-ion channels

“…From powder data they derived a disordered structure type without a Ni II /Te VI honeycomb-like ordering and Li I /Ni II mixed occupation of the 8b and the two 16g sites. 22 Our singlecrystal investigations confirmed the missing honeycomb-like ordering and furthermore, Li 3 Co 1.06(1) TeO 6 exhibits a comparatively high-order three-dimensional lattice of two interpenetrating substructures. These two substructures consist of a lithium-oxygen and a cobalt/tellurium-oxygen structure part.…”

“…Kumar et al reported on a tellurium containing mixed oxide crystallizing in a disordered Fddd structure type without a M II /Te VI honeycomb-like ordering. 22 The given unit cell parameters of this compound (Li 2 Ni 2 TeO 6 : a = 589.21 (7), b = 859.9(1), c = 1769.1 (2) pm) are nearly the same as those of the here presented Li 3 Co 1.06(1) TeO 6 , also crystallizing without the honeycomb-like ordering in an orthorhombic unit cell with Fddd symmetry. Other previously known oxides with an orthorhombic Fddd symmetry are Li 3 M II 2 LO 6 (M = Ni, Co, Mg; L = Nb, Ta, Sb) [11][12][13][14] with the exception of Li 3 Co 2 NbO 6 .…”

“…During various refinement cycles, mixed occupations of the cobalt and lithium sites were tested. A simultaneous refinement of both Li sites together with the Co site as Li/Co mixed occupied sites according to Kumar et al 22 was not possible. In addition to this, refinements of the under-occupied Co site as the mixed Li/Co site resulted in a compound with a Li/Co ratio larger than that detected by the ICP measurements.…”

Interesting cationic (Li+/Fe3+/Te6+) variations in new rocksalt ordered structures

“…Two different polytypes I and II of Li 2 Ni 2 TeO 6 were also synthesized respectively by the low temperature ion-exchange reaction and by high temperature solid state method. 20…”

Flux-mediated syntheses, structural characterization and low-temperature polymorphism of the p-type semiconductor Cu2Ta4O11

“…The flux synthesis method is a versatile and advantageous technique for the modification of chemical composition, structure, and particle morphologies and sizes, as highlighted in recent reviews [7,11]. Reactions within molten-salt fluxes have been shown to yield faster reaction rates at relatively lower temperatures, highlyfaceted particles with more homogeneous particle distributions, and decreased activation barriers for the growth of solid-state compounds with limited thermal stability [12][13][14]. Changes in chemical composition and single-crystal particle morphologies of metal-oxides have been found to impact their physical properties, including their optical, electronic and photocatalytic properties.…”