Acceptor doping in the proton conductor SrZrO 3

), and this is detrimental to proton conductivity. Due to its larger ionic radius, Y exhibits a greater tendency than Sc to self-compensate at the Sr site. We also investigated the proton-dopant association. The binding energy of a proton to a negatively charged acceptor impurity is 0.41 eV for Sc and 0.31 eV for Y, indicating that proton transport is limited by trapping at impurity sites.