Li3Ni2TaO6: A novel rock salt superstructure phase with partial cation order

Abstract

The new phase Li,Ni2Ta06 has a novel rock salt superstructure, a = 8.4259(3) A, b = 5.9073(3) A, c = 17.7329 A, Fddd. Within the cubic-close-packed oxide array, Ta occupies one set of octahedral sites giving isolated TaO, octahedra which edge-share with Li/NiO, octahedra. Li and Ni are distributed non-randomly over three other sets of octahedral sites with Li : Ni occupancy ratios of 0.73 : 0.27, 0.59 : 0.41 and 0.55 : 0.45, respectively. The higher Li : Ni ratio of the first set, 0.73:0.27 may be associated with cation-cation repulsion effects since this site is closest to Ta. Li,Ni,Ta06 is a very modest semiconductor with conductivity of ca. 4 x l o p 6 R-' cm-' at 300 "C and activation energy 0.77 eV; the disorder in the Li' site occupancy is, therefore, static and does not yield significant levels of Li+ ion conductivity.

Continuous Order–Disorder Transition in Li3Ni2NbO6and Cr-Doped Li3Ni2NbO6Rock Salt Structures

“…Samples were quenched in air or, for the higher In the field of rock salt superstructure phases, the recently discovered family, Li 3 M 2 XO 6 (M ϭ Mg, Co, Ni; temperatures, into Hg. Heating times at 1100ЊC and above were limited to about 10 min in order to prevent possible X ϭ Nb, Ta, Sb) is most unusual in showing a partial order of the cations (1,2). The high valency X atoms occupy lithia loss by volatilization.…”

Na3Ca2TaO6, a rock-salt superstructure phase with a fully ordered cation arrangement

“…These data suggested ionic conduction of Na 3 Ca 2 TaO 6 . Ionic conduction was not detected for Li 3 Ni 2 TaO 6 with partial cation ordering (Fletcher et al, 1994).…”

“…The crystal structures of a series of quaternary compounds containing lithium, i.e. Li 3 M 2 XO 6 (M = Mg, Co, Ni; X = Nb, Ta), were analyzed by X-ray and/or neutron powder diffraction (Fletcher et al, 1994;Mather et al, 1995). These compounds have a rock-salt superstructure with partial cation order.…”

Synthesis of Li3Cu2SbO6, a New Partially Ordered Rock Salt Structure

“…In the latter case the cations can be disordered to give the simple face centred cubic structure or can exhibit a range of cation ordering arrangements. Recently, a family of structures, Li M XO : M"Mg, Co, Ni; X"Nb, Ta, Sb, has been shown to exhibit partial cation order but with an unusual nonstatistical occupancy of the Li/M sites [1,2]: there are three sets of sites for the Li/M cations and the distribution over these sites is nonrandom and varies with the nature of M (and X). The partial cation order appears to be an equilibrium arrangement at low temperatures, although in the case of Li Ni NbO , the cation arrangement becomes increasingly statistical over the range 1100-1300°C, as the structure undergoes a continuous (partial) order-disorder transition [3].…”