Identification of the Li sites in the Li ion conductor, Li6SrLa2Nb2O12, through neutron powder diffraction studies

Synthesis and conductivities of the garnet-related Li ion conductors, Li5Ln3Sb2O12 (Ln=La, Pr, Nd, Sm, Eu)

“…In agreement with the neutron diffraction structural studies by Cussen and our previous structural studies of Li 6 [11][12][13]16], the former refinement resulted in a poor fit and a generally unstable refinement, and so further refinement continued with the Cussen structural model.…”

“…This work identified the space group as Ia-3d, with the Li occupying tetrahedral and distorted "octahedral" sites. Subsequently this structural interpretation has been confirmed by further work by Cussen et al, and a similar study of the higher Li content phase Li 6 SrLa 2 Nb 2 O 12 within our group [12,13]. In the latter it was shown that the distorted nature of the "octahedral site" gave a coordination closer to 4 coordinate, the remaining two Li-O bonds being quite long (>2.6 Å).…”

“…The second garnet phase could be a result of Li volatility from the surface under the high synthesis temperatures, and so may suggest a certain degree of non-stoichiometry in these systems, which needs further investigation. Further evidence in support of this conclusion is the significant spread of cell parameters reported in the literature for the The final refined structural parameters are given in [11,12,16], with Li present in both the ideal garnet tetrahedral site, and a more distorted second site normally vacant in the garnet structure. In agreement with our previous studies [12,16], a close inspection of the second sites suggests that the coordination is occ.…”

Synchrotron study of the garnet-type oxide Li6CaSm2Ta2O12

“…The ionic conductivity was enhanced through the increase of the Li content via partial substitution of trivalent La 3+ by divalent alkaline earth ions (Murugan et al, 2007). The structure of the title compound is closely related to that of Li 6 SrLa 2 Ta 2 O 12 (Percival & Slater, 2007). Li1 atoms are located at site 24d (tetrahedral), Li2 atoms at site 96h (distorted octahedral), Sm/Ca atoms are at site 24c (cubic), Ta atoms at site 16a (octahedral), and O atoms at general site 96h ( …”

“…Recently, high Li-ion conductivity was discovered in garnet-related compounds such as Li 5 La 3 M 2 O 12 (M = Nb, Ta), see: Thangadurai et al (2003); Cussen (2006). For studies focused on the substitution of La 3+ by divalent alkaline earth ions (Ca, Sr, Ba), see: Murugan et al (2007); Thangadurai & Weppner (2005a,b); O'Callaghan & Cussen (2007); Percival & Slater (2007). For indexing the powder diffraction pattern, see : Boultif & Louë r (2004).…”