Lithiotantite, ideally LiTa3O8

Luiz A.D. Menezes Filho, Hexiong Yang, Robert T. Downs, Mário L. S. C. Chaves, Aba C. Persiano
2012 Acta Crystallographica Section E  
Key indicators: single-crystal X-ray study; T = 293 K; mean (Ta-O) = 0.005 Å; disorder in main residue; R factor = 0.028; wR factor = 0.058; data-to-parameter ratio = 27.9. Lithiotantite (lithium tritantalum octaoxide) and lithiowodginite are natural dimorphs of LiTa 3 O 8 , corresponding to the laboratory-synthesized L-LiTa 3 O 8 (low-temperature form) and M-LiTa 3 O 8 (intermediate-temperature form) phases, respectively. Based on single-crystal X-ray diffraction data, this study presents the
more » ... irst structure determination of lithiotantite from a new locality, the Murundu mine, Jenipapo District, Itinga, Minas Gerais, Brazil. Lithiotantite is isotypic with LiNb 3 O 8 and its structure is composed of a slightly distorted hexagonal close-packed array of O atoms stacked in the [101] direction, with the metal atoms occupying half of the octahedral sites. There are four symmetrically non-equivalent cation sites, with three of them occupied mainly by (Ta 5+ + Nb 5+ ) and one by Li + . The four distinct octahedra 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)O 6 octahedra (M1 and M2), whereas the B chains consist of alternating (Ta,Nb)O 6 and LiO 6 octahedra (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 octahedra, 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 Ta 5+ for M3 in the B chain. The refined composition of the crystal investigated is Li 0.
doi:10.1107/s1600536812013566 fatcat:schv6sa6bzff5pqa7ecvsm5loq