Framework 'interstitial' oxygen in La(10)(GeO(4))(5-)(GeO(5))O(2) apatite electrolyte.
Oxygen conduction at low temperatures in apatites make these materials potentially useful as electrolytes in solid-oxide fuel cells, but our understanding of the defect structures enabling ion migration is incomplete. While conduction along [001] channels is dominant, considerable inter-tunnel mobility has been recognized. Using neutron powder diffraction of stoichiometric 'La(10)(GeO(4))(6)O(3)', it has been shown that this compound is more correctly described as an La(10)(GeO(4))(5-)(GeO(5))O(2) apatite, in which high concentrations of interstitial oxygen reside within the channel walls. It is suggested that these framework interstitial O atoms provide a reservoir of ions that can migrate into the conducting channels of apatite, via a mechanism of inter-tunnel oxygen diffusion that transiently converts GeO(4) tetrahedra to GeO(5) distorted trigonal bipyramids. This structural modification is consistent with known crystal chemistry and may occur generally in oxide apatites.
Pramana
Stevin S
SS
Nanyang Technological University, School of Materials Science and Engineering, 50 Nanyang Avenue, 639798 Singapore.
Klooster
Wim T
WT
White
T J
TJ