title: Structural study of the apatite Nd₈Sr₂Si₆O₂₆ by Laue neutron diffraction and single-crystal Raman spectroscopy.
abstract: A single-crystal structure determination of Nd8Sr2Si6O26 apatite, a prototype intermediate-temperature electrolyte for solid oxide fuel cells grown by the floating-zone method, was completed using the combination of Laue neutron diffraction and Raman spectroscopy. While neutron diffraction was in good agreement with P6₃/m symmetry, the possibility of P6₃ could not be convincingly excluded. This ambiguity was removed by the collection of orientation-dependent Raman spectra that could only be consistent with P6₃/m. The composition of Nd8Sr2Si6O26 was independently verified by powder X-ray diffraction in combination with electron probe microanalysis, with the latter confirming a homogeneous distribution of Sr and the absence of chemical zonation commonly observed in apatites. This comprehensive crystallochemical description of Nd8Sr2Si6O26 provides a baseline to quantify the efficacy of cation vacancies, oxygen superstoichiometry, and symmetry modification for promoting oxygen-ion mobility.
authors.affiliation: School of Materials Science and Engineering, Nanyang Technological University , 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Tao
authors.initials: T
authors.lastname: An
authors.forename: Alodia
authors.initials: A
authors.lastname: Orera
authors.forename: Tom
authors.initials: T
authors.lastname: Baikie
authors.forename: Jason S
authors.initials: JS
authors.lastname: Herrin
authors.forename: Ross O
authors.initials: RO
authors.lastname: Piltz
authors.forename: Peter R
authors.initials: PR
authors.lastname: Slater
authors.forename: Tim J
authors.initials: TJ
authors.lastname: White
authors.forename: María L
authors.initials: ML
authors.lastname: Sanjuán