Structural Study of the Apatite Nd 8 Sr 2 Si 6 O 26 by Laue Neutron Diffraction and Single-Crystal Raman Spectroscopy

• Main Authors: An, Tao, Orera, Alodia, Baikie, Tom, Herrin, Jason S., Piltz, Ross O., Slater, Peter R., Sanjuán, María L., White, Timothy John
• Other Authors: School of Materials Science and Engineering
• Format: Article
• Language: English
• Published: 2016
• Subjects: Solid electrolyte; Neodymium silicate; Single crystal; Raman spectrum; Neutron diffraction; Apatite
• Online Access: https://hdl.handle.net/10356/82206; http://hdl.handle.net/10220/39816
• Institution: Nanyang Technological University

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.