Crystal chemistry of lithium in octahedrally coordinated structures. I. Synthesis of Ba8(Me6Li2)O24 (Me = Nb or Ta) and Ba10(W6Li4)O30. II. The tetragonal bronze phase in the system BaONb2O5Li2O

The preparation, single crystal growth, and crystallographic properties of a close-packed, eight-layer, hexagonal (a = 5.803 Å, c = 19.076 Å) modification having the stoichiometry Ba₈Nb₆Li₂O₂₄ and of a close-packed, ten-layer, hexagonal (a = 5.760 Å, c = 23.742 Å) phase with Ba₁₀W₆Li₄O₃₀ stoichiometry are discussed. The isostructural Ba₈Ta₆Li₄O₂₄ form of the eight-layer phase was also prepared (a = 5.802 Å, c = 19.085 Å). Proposed crystal structures involve the pairing of lithium and metal (Nb, Ta, or W) octahedra to yield face-sharing units. The relationship of this phenomenon to other known close-packed phases containing Li is demonstrated. An investigation of the Ba₈Nb₆Li₂O₂₄Ba₁₀W₆Li₄O₃₀ system is reported.A tetragonal bronze phase homogeneity region was delimited at 1200°C in the BaONb₂O₅Li₂O system. A new orthorhombic phase (a = 10.197 Å, b = 14.882 Å, c = 7.942 Å) was prepared with the stoichiometry Ba₄Li₂Nb₁₀O₃₀.