Blocking grain boundaries in acceptor-doped BaZrO3 proton conductors

M. Shirpour, R. Merkle

Among the oxide proton conductors, Y-doped BaZrO3 with excellent chemical stability and relatively high total conductivity is an interesting electrolyte material for intermediate temperature fuel cells. Its main drawback is the blocking character of the grain boundaries (GBs) combined with small grain size. To identify the origin of the blocking character and to develop means for improving the grain boundary properties, potential reasons for blocking effect are investigated. Evidence for applicability of the space charge model (positive GB core and depletion of positively charged protons, oxygen vacancies and holes in adjacent space charge zones) is provided by the bias-dependence of GB resistance and capacitance (Fig. 1), and the increasing GB conductivity with increasing acceptor dopant segregation upon annealing (Fig. 2) which helps to compensate the positive GB core charge.

Figure 1: (a) microelectrodes on large-grained Ba(Zr,Y)O3-d sample, (b) shrinking of GB semicircle in impedance spectrum of a single GB under DC bias.

Figure 2: (a) increase of GB conductivity upon annealing (grain size remains unchanged). (b) accumulation of acceptor dopants in GB region, measured by TEM-EDX.

see also poster1  poster2  


M. Shirpour, B. Rahmati, W. Sigle, P. A. van Aken, R. Merkle, and J. Maier
Dopant Segregation and Space Charge Effects in Proton-Conducting BaZrO3 Perovskites
Journal of Physical Chemistry C 116(3), 2453-2461 (2012)   DOI: 10.1021/jp208213x

M. Shirpour, C.T. Lin, R. Merkle, and J. Maier
Nonlinear electrical grain boundary properties in proton conducting Y-BaZrO3 supporting the space charge depletion model
Physical Chemistry Chemical Physics 14(2), 730-740 (2012)  DOI: 10.1039/C1CP22487E

M. Shirpour, R. Merkle, and J. Maier
Space charge depletion in grain boundaries of BaZrO3 proton conductors
Solid State Ionics  225 (2012) 304   DOI: 10.1016/j.ssi.2012.03.026

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