Lithio-tantite, ideally LiTa₃O₈

Lithio-tantite (lithium tritantalum octa-oxide) and lithio-wodg-inite are natural dimorphs of LiTa₃O₈, corresponding to the laboratory-synthesized L-LiTa3O8 (low-temperature form) and M-LiTa3O8 (inter-mediate-temperature form) phases, respectively. Based on single-crystal X-ray diffraction data, this study presents the first structure determination of lithio-tantite from a new locality, the Murundu mine, Jenipapo District, Itinga, Minas Gerais, Brazil. Lithio-tantite is isotypic with LiNb3O8 and its structure is composed of a slightly distorted hexa-gonal close-packed array of O atoms stacked in the [-101] direction, with the metal atoms occupying half of the octa-hedral sites. There are four symmetrically non-equivalent cation sites, with three of them occupied mainly by (Ta⁵⁺ + Nb⁵⁺) and one by Li⁺. The four distinct octa-hedra share edges, forming two types of zigzag chains (A and B) extending along the b axis. The A chains are built exclusively of (Ta,Nb)O6 octa-hedra (M1 and M2), whereas the B chains consist of alternating (Ta,Nb)O6 and LiO6 octa-hedra (M3 and M4, respectively). The average M1 - O, M2 - O, M3 - O and M4 - O bond lengths are 2.011, 2.004, 1.984, and 2.188 Å, respectively. Among the four octa-hedra, M3 is the least distorted and M4 the most. The refined Ta contents at the M1, M2 and M3 sites are 0.641 (2), 0.665 (2), and 0.874 (2), respectively, indicating a strong preference of Ta⁵⁺ for M3 in the B chain. The refined composition of the crystal investigated is Li₀.₉₆Mn₀. ₀₃Na₀.₀₁Nb₀.₈₂Ta ₂.₁₈O₈.