Dr. Frédéric Blanc ，Department of Chemistry and Stephenson Institute for Renewable Energy, University of Liverpool
Conference Room of Basic Energy Science Building
July 2, 2015 (Thursday) 9:00am
Abstract
We shall present examples of the investigation of the defects chemistry in fast ion conductors materials by multinuclear solid state NMR spectroscopy.
An approach combining experimental multinuclear NMR spectroscopy with density functional theory total energy and GIPAW NMR calculations yields a comprehensive understanding of the structural and defect chemistries of Sr and Mg-doped LaGaO3 and demonstrates that Ga-VO-Ga (VO = oxygen vacancy) environments are favored while Mg sites remain six-fold coordinated, albeit with significant structural disorder. The 17O NMR spectra reveal distinct resonances to anions occupying equatorial and axial positions with respect to the GaV-VO axis.1,2
Fergusonite materials LaNbO4 have shown extremely promising fast oxide ion conduction when doped with W (e.g. LaNb0.92W0.08O4+d).3 These materials differ from others such as the Sr and Mg-doped LaGaO3 perovskites as the conduction mechanism is based on interstitial oxygens rather than oxygen vacancies. High field 93Nb NMR data recorded under very fast MAS conditions on LaNb0.92W0.08O4+d allow the observation of local nobium environments not present in LaNbO4 and compatible with the presence interstitial oxygens.4 Similarly, insights into the existence of interstitial oxygens and their
location in new Ge doped langasite La3Ga5GeO14 phases were obtained from 71Ga and 17O NMR.5
Calculation of the energetics of aliovalent substitution into the LiMgPO4 olivine suggests that replacement of Mg2+ by In3+ is the most effective way to introduce lithium vacancies and thus generate lithium ion conductivity. An order of magnitude increase in the high temperature hopping rates probed by 7Li NMR, and over two orders of magnitude increase in the room temperature Li+ ion conductivity measured by impedance spectroscopy is observed on introduction of In3+ ions and Li vacancies, experimentally confirming the calculations.6
(1) Blanc, F. et al. J. Am. Chem. Soc. 2011, 133, 17662. (2) Blanc, F. et al. Solid State Nucl. Magn. Reson.
2012, 42, 87. (3) Packer, R. J. et al. J. Mater. Chem. 2006, 16, 3503. (4) Hanna, J. V. et al. Chem. Eur. J.
2010, 16, 3222. (5) Diaz-Lopez, M. et al. in preparation. (6) Enciso-Maldonado, L. et al. Chem. Mater.
2015, 27, 2074.
Ying Shi （9128）