Cation dopant sites in the CaZrO3 proton conductor: a combined EXAFS and computer simulation study

Ceramics of pure, 5% Yb- and 5% Nd-doped CaZrO3 were prepared and investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy and computer simulation techniques. The EXAFS results reveal that Yb3+ behaves as an acceptor-dopant, substituting for Zr4+, while the larger Nd3+ lanthanide dopant behaves as a donor-dopant, substituting for Ca2+. The EXAFS results are borne out by atomistic modelling where small lanthanide dopants are predicted to substitute on the Zr4+ site (with oxygen vacancy compensation that is vital for proton incorporation), while larger lanthanide dopants substitute on the Ca2+ site. The drop in proton conductivity exhibited for the larger lanthanides may be related to the reduced oxygen vacancy concentration arising from dopant site-selectivity.