[The arsenate Na3Fe2(AsO4) 3: structural study at low temperature and simulation of conduction properties of alkaline cations].

The crystal structure of the low-temperature garnet-like form of trisodium diiron(III) triarsenate, Na(3)Fe(2)(AsO(4))(3), exhibits a three-dimensional framework with small tunnels running along the [111] direction, in which the Na(+) cations are located. This study demonstrates the structural origins of the different ionic conductivities of the low- and high-temperature forms. Sodium conduction properties are simulated by means of the bond-valence-sum (BVS) model; the correlations between the low- and high-temperature crystal structures are discussed. The As, Fe and Na atoms lie on special positions (Wyckoff symbols 24d, 16a and 24c, respectively).