Vacancy association energy in scandium doped ceria: super(45)Sc MAS NMR and 2D exchange spectroscopy study

• Published in: Solid state ionics 2014-12, Vol.267, p.49-53
• Main Authors: Poder, Reio, Subbi, Juhan, Kooskora, Helgi, Heinmaa, Ivo
• Format: Article
• Language: English
• Subjects: Cerium oxide; Exchange; Ion exchangers; Lattice vacancies; Nuclear magnetic resonance; Scandium; Two dimensional; Vacancies
• ISSN: 0167-2738
• DOI: 10.1016/j.ssi.2014.09.010

Oxygen vacancy exchange between Sc ions in 0.5% Sc-doped ceria Sc sub(0.005)Ce sub(0.995)O sub(0.9975) is investigated by means of 2D exchange spectroscopy (EXSY). super(45)Sc NMR spectrum of Sc-doped ceria contains two peaks-one corresponding to Sc ions coupled with an oxygen vacancy (Sc-7), and the other corresponding to Sc ions in a regular lattice site surrounded by eight oxygen ions (Sc-8). The vacancy exchange between these two Sc sites generates the cross-peaks in the EXSY spectrum. Relative amplitudes of the cross-peaks provide direct values of the exchange frequency at a given temperature. Arrhenius analysis of the exchange frequency gives the activation energy E sub(a) = 1.18 eV for the vacancy hopping between Sc sites. Most of this energy barrier is due to association energy which binds the vacancy to Sc super(3+). Large dopant-vacancy association energy in Sc doped ceria is demonstrated by super(45)Sc NMR spectrum of La/Sc doubly doped sample, Sc sub(x)La sub(x)Ce sub(1 - 2x)O sub(2 - x), x = 0.005, where the only line of Sc-7 site shows that all vacancies are bound by Sc super(3+) ions.