title: Interstitial Oxide Ion Distribution and Transport Mechanism in Aluminum-Doped Neodymium Silicate Apatite Electrolytes.
abstract: Rare earth silicate apatites are one-dimensional channel structures that show potential as electrolytes for solid oxide fuel cells (SOFC) due to their high ionic conductivity at intermediate temperatures (500-700 °C). This advantageous property can be attributed to the presence of both interstitial oxygen and cation vacancies, that create diffusion paths which computational studies suggest are less tortuous and have lower activation energies for migration than in stoichiometric compounds. In this work, neutron diffraction of Nd(28+x)/3AlxSi6-xO26 (0 ≤ x ≤ 1.5) single crystals identified the locations of oxygen interstitials, and allowed the deduction of a dual-path conduction mechanism that is a natural extension of the single-path sinusoidal channel trajectory arrived at through computation. This discovery provides the most thorough understanding of the O(2-) transport mechanism along the channels to date, clarifies the mode of interchannel motion, and presents a complete picture of O(2-) percolation through apatite. Previously reported crystallographic and conductivity measurements are re-examined in the light of these new findings.
authors.affiliation: Nanyang Technological University , School of Materials Science and Engineering, 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Tao
authors.initials: T
authors.lastname: An
authors.affiliation: Energy Research Institute @ NTU (ERI@N), Nanyang Technological University , Singapore 637553, Singapore.
authors.forename: Tom
authors.initials: T
authors.lastname: Baikie
authors.affiliation: ICMA, CSIC-Universidad de Zaragoza , 50009 Zaragoza, Spain.
authors.forename: Alodia
authors.initials: A
authors.lastname: Orera
authors.affiliation: Bragg Institute , Australian Science and Technology Organisation, Lucas Heights, New South Wales 2234, Australia.
authors.forename: Ross O
authors.initials: RO
authors.lastname: Piltz
authors.affiliation: RWTH Aachen, Institute of Crystallography and Jülich Centre for Neutron Sciences (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ) , Lichtenbergstraße 1, 85747 Garching, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Meven
authors.affiliation: School of Chemistry, University of Birmingham , Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Slater
authors.affiliation: Singapore Institute of Manufacturing Technology (SIMTech), Agency for Science, Technology and Research (A*STAR) , 71 Nanyang Drive, 638075, Singapore.
authors.forename: Jun
authors.initials: J
authors.lastname: Wei
authors.affiliation: ICMA, CSIC-Universidad de Zaragoza , 50009 Zaragoza, Spain.
authors.forename: María L
authors.initials: ML
authors.lastname: Sanjuán
authors.affiliation: Nanyang Technological University , School of Materials Science and Engineering, 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: T J
authors.initials: TJ
authors.lastname: White