Solid state NMR spin-lattice relaxation investigation of oxygen dynamics in scandium doped ceria from 60 to 1073 K

Abstract

Abstract Scandium spin dynamics in scandium doped ceria has been addressed first time through spin-lattice relaxation temperature dependence. Scandium spin-lattice relaxation temperature dependence in 0.5% scandium doped ceria matrix has been measured in the range between 60 K and 1073 K in magnetic fields 4.7 T and 8.5 T. The temperature dependence revealed four separate processes, two for 8-coordinated scandium and two for 7-coordinated scandium. However, none of these processes could be associated with oxygen vacancy hopping processes, directly responsible for ion conductivity in scandium doped ceria. We have established that for 7-Sc, the high temperature process is vacancy hopping around the scandium ion with activation energy 0.37 eV and the low temperature process is a Raman process involving local vibrations with characteristic energy 26 meV (208 cm − 1 ). For 8-Sc, the high temperature process is assigned to hopping between potential wells with different energy minima with apparent activation energy of 0.28 eV. We have shown that in this case the apparent activation energy of the process does not correspond to barrier height for hopping, but to barrier height plus energy difference between minima of corresponding wells. The low temperature process is again a Raman process involving local vibrations with even lower characteristic energy 20 meV (160 cm − 1 ).