Oxygen vacancy segregation in grain boundaries of BaZrO3 using interatomic potentials

Abstract

We have used classical interatomic potentials to determine the structure, interface energy and oxygen vacancy segregation energies of eight different grain boundaries (GBs) in BaZrO 3 with tilt axis [110]. Two of these have been studied previously with density functional theory and the agreement is satisfactory. The results suggest that oxygen vacancies prefer to reside near the boundary interface for all these GBs. The minimum segregation energies range between −1.86 eV and −0.57 eV, and the typical core width is about 10Å. The resulting depletion layers have been evaluated using a thermodynamic space-charge model. Space-charge potential barriers between 0.2-0.8 eV were obtained with dopant concentrations of 5 % and 10 %.

Theoretical modeling of defect segregation and space-charge formation in the BaZrO3 (210)[001] tilt grain boundary

“…5 it can be seen that both protons and oxygen vacancies segregate to the grain boundary with minimum segregation energies of −1.45 eV and −1.32 eV for vacancies and protons, respectively. A similar vacancy segregation energy was obtained for the (112)[110] grain boundary using DFT [20], and for a set low angle [110] grain boundaries using classical interatomic potentials [19]. The proton segregation is much stronger for this grain boundary compared to structures previously studied by our group [20] and Polfus et al [21] where the segregation energy is about −0.8 eV for all boundaries.…”

“…An oxygen vacancy segregation energy of about −1.5 eV has been found in other tilt grain boundaries of BaZrO 3 [19,20] suggesting that this is a typical value for vacancy segregation. The proton segregation tendency is found to be larger in the present study compared with some previous investigations [20,21], with segregation energy −1.3 eV compared with −0.8 eV in [20,21].…”

“…The results suggest that both defect species do segregate to the GB core but the strength of the segregation varied among the boundaries, favoring vacancies in some and protons in others [18,20]. We have also studied oxygen vacancy segregation in more complex structured low-angle [110] tilt grain boundaries using interatomic potentials, where we concluded that segregation to all considered boundaries was favorable [19]. Furthermore, Polfus et al [21] have studied defect segregation to the (111)[110] GB using DFT and their results regarding oxygen vacancy and proton segregation are in agreement with our results [20].…”

“…In turn, the potential depletes the surrounding regions of mobile charge carriers thus limiting the conductivity [9,10]. The spacecharge model has been applied to BaZrO 3 by several research groups where the space-charge potentials have been determined based on both experiments [6,8,[11][12][13][14][15][16] and theoretical modeling [17][18][19][20][21].…”

Proton Conduction in Nonstoichiometric ∑3 BaZrO3 (210)[001] Tilt Grain Boundary Using Density Functional Theory

“…[1][2] Among many proton-conductors, the acceptor-doped barium zirconate (BaZrO 3 , BZO) has been intensively studied as an electrolyte of protonic ceramic fuel cell (PCFC) because of its high proton conductivity through the grain interior and sound chemical stability. [3][4][5][6][7][8][9][10][11][12] However, the low proton conductivity across the grain boundary compared to that of grain interior has been recognized as a critical issue. [3][4][5][6][7][8][9][10][11][12][13] The low proton conductivity of BZO grain boundary has been often interpreted with the space charge layer (SCL) model, in which the positively charged protons accumulate in grain boundary.…”