Speaker
Mr
Matthew Tate
(Bragg Institute, ANSTO)
Description
Oxide ion conductors are used in a wide variety of applications, including oxygen sensors and separation membranes, but are undergoing significant study for their use in solid oxide fuel cells (SOFCs), which allow for the direct conversion of chemical to electrical energy. Apatite-type silicates and germanates, La9.33+x(TO4)6O2+3x/2 (T = Si,Ge), have exhibited high oxide ion conductivities, potentially allowing for their use in SOFCs.
Apatite-type compounds have the general formula, [AI4][AII6][TO4]6X2±δ, (A = alkaline or rare earth metal, or Pb; T = Ge, Si, P, V; X = O, OH, halides) and can be thought of as comprised of a framework of AI4(TO4)6 with flexible cavities containing AII6X2 units. The structures of apatite-type materials are primarily hexagonal, with the remainder being monoclinic, with several triclinic examples known. The origin of the triclinic structure is thought to be partly due to the size differences between the units comprising the framework and those within the cavities. The inclusion of interstitial oxide ions have been shown to promote the triclinic distortion, potentially caused by further expansion of the framework.
Three novel Bi(III)-containing lanthanum germanium apatite compounds (Bi2La8[(GeO4)6
]O3, Bi4Ca4La2[(VO4)2(GeO4)4]O2, and Bi4Ca2La4[(GeO4)6]O2) were synthesised by a solid state synthetic method, before undergoing AC impedance spectroscopy experiments to study their electrical properties. The Bi2La8[(GeO4)6
]O3 compound has been identified as being the first bismuth containing apatite with a triclinic structure, whilst the Bi4-containing compounds possess hexagonal structures. All samples show high levels of conductivity, with the triclinic sample possessing higher conductivity values than the hexagonal samples at high temperature.
Primary author
Mr
Matthew Tate
(Bragg Institute, ANSTO)
Co-authors
Prof.
Garry McIntyre
(Bragg Institute, ANSTO)
Dr
Ivana Evans
(Durham University, UK)
