Transition metal-substituted lithium pnictogenide phases.: Synthesis and crystal structure determinations of novel phases in the Li-M-X systems (M = V, Nb, Ta; X = P, As)

Li-M-X systems have been investigated and crystal structures of several phases determined. Li7NbP4 crystallizes in the anti-fluorite-type structure (cubic, Fm (3) over barm, a = 5.996(1) Angstrom, Z = 1, R(F) = 3.02%). LiNbAs2 and Li4.54V1.22As4 display the blende-type structure, cubic F (4) over bar 3m space group (LiNbAs2:a = 6.309(1) Angstrom, Z = 2, R(F)= 2.12%; Li4.54V1.22As4:a = 6 167(1) Angstrom, Z = 1, R(F) = 1,49%), In all compounds, the transition metal statistically occupies some of the tetrahedral sites with lithium, For Li4.54V1.22As4. one of the octahedral sites of the fcc lattice is partially filled with lithium. This feature is also observed for the homologue compounds Li-x(Li3.20Nb0.80)As-4 and Li-x(Li3.64Ta0.36)As-4, 0<x<less than or equal to>4 (F (4) over bar 3m, Z = 1, a = 6,190(3) and 6.184(3) Angstrom, R(F) = 1.76 and 3,42%, respectively). (C) 2001 Academic Press.