Ordering and entangled dynamics of oxygen vacancies and charges in CeO2-x

A. M. LLOIS; Y. GAO; G. E. MURGIDA; V. FERRARI; M. V. GANDUGLIA PIROVANO; D. ZHANG

Buenos Aires

Conferencia; 27th International Conference on Statistical Physics, StatPhys 27,; 2019

The known ability of ceria (CeO2) to release, capture, andtransport oxygen is the basis of its outmost importance in catalysisand also in other applications such as fuel cells, sensors, andresistive switching. In order to develop and optimize ceria baseddevices, the understanding of the ordering and the mobility of theoxygen vacancies and the charges left behind, upon vacancy formation,is crucial. To tackle this problem, we use density functional theoryin combination with statistical thermodynamics and ab initiomolecular dynamics (AIMD).The two electrons released during a vacancy formation localize in twoCe ions, changing their valence from Ce4+ to Ce3+.The Ce3+ ions are small polarons and localize, preferably, at Ce sites next nearest neighbors of the vacancy [1,2]. In reducedceria (111) surface, which is the most stable one, the vacancieslocalize mainly in the oxygen subsurface and present a repulsiveinteraction among them that vanishes at third nearest neighborsdistance [1]. In bulk ceria we note that the repulsive interactionbetween vacancies reaches a minimum at second or third neighboringsites distance, suggesting the formation of vacancy clusters [2].Based on recent experimental studies that report periodic arranges ofvacancies in reduced ceria surfaces, we modeled the distribution ofvacancies and polarons for each periodicity and calculated thestability range of each phase as a function of oxygen pressure andtemperature [3]. We also proposed a new quasi stable bulk structureof Ce3O5 [4] that can explain the formation ofone of the observed surface structures. Using AIMD simulations weanalized the migration of oxygen vacancies and the polaron hoppingsin reduced ceria (111) surface in the range of 300-900K [5].Different dynamic regimens were obtained for 300, 500, 700 and 900K.We observed a clear entanglement between the dynamics of vacanciesand polarons and identified different collective migrationmechanisms.p { margin-bottom: 0.1in; direction: ltr; color: rgb(0, 0, 0); line-height: 120%; }p.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; }p.cjk { font-family: "Noto Sans CJK SC Regular"; font-size: 12pt; }p.ctl { font-family: "FreeSans"; font-size: 12pt; }