Crystal data for a new family of phases, Li3Mg2XO6:X=Nb, Ta, Sb

Chemical Pressure Effect on the Stabilization of Rock-Salt ZnO-Lin-2MeOn-1 Solid Solutions Synthesized at High Pressure

Metastable ZnO-Lin-2MeOn-1 (Me = Sc3+, Ti4+, Ta5+) solid solutions with a rock-salt structure were synthesized through the solid-state reaction of ZnO with Lin-2Men+On-1 (n = 3, 4, 5) complex oxides at 7.7 GPa and 1300-1500 K. In all investigated systems, single-phase rock-salt solid solutions can be quenched down to ambient conditions in a wide (up to 80 mol% ZnO) concentration range. The phase composition, thermal stability, and thermal expansion of the recovered rock-salt solid solutions were studied by synchrotron powder X-ray diffraction. At ambient pressure, these solid solutions exhibit high thermal stability (up to 1000 K), with the decomposition temperature and decomposition products depending on the nature of the multiple charge cations.

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

A tellurate compound with Co^II/Co^III mixed valence states and lithium ions within orthogonally oriented channels was realized in Li₃Co_1.06(1)TeO₆. The single-crystal structure determination revealed two independent and interpenetrating Li/O and (Co,Te)/O substructures with octahedral oxygen coordination of the metal atoms. In contrast to other mixed oxides, a honeycomb-like ordering of CoO₆ and TeO₆ octahedra was not observed. Li₃Co_1.06(1)TeO₆ crystallizes orthorhombically with the following unit cell parameters and refinement results: Fddd, a = 588.6(2), b = 856.7(2), c = 1781.5(4) pm, R₁ = 0.0174, wR₂ = 0.0462, 608 F² values, and 33 variables. Additional electron density in tetrahedral voids in combination with neighboring face-linked and under-occupied octahedral lithium sites offers an excellent possible diffusion pathway for lithium ions. According to the symmetry of the crystal structure the diffusion pathways in Li₃Co_1.06(1)TeO₆ were found in two orthogonal orientations. The Co^II/Co^III mixed valence was investigated via X-ray photoelectron spectroscopy (XPS), revealing a composition comparable to that derived from single-crystal X-ray diffractometry. Magnetic susceptibility measurements underlined the coexistence of Co^II and Co^III, the title compound, however, showed no magnetic ordering down to low temperatures. The ionic conductivity of Li₃Co_1.06(1)TeO₆ was determined via alternating current (AC) electrochemical impedance spectroscopy and was found to be in the range of 1.6 × 10^-6 S cm^-1 at 573 K.

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

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).