Combined experimental and modelling studies of proton conducting La1-xBa1+xGaO4-x/2: proton location and dopant site selectivity

In this paper, neutron diffraction studies are reported on the La1-xBa1+xGaO4-x/2 system in order to locate the proton sites. Difference Fourier maps suggested the presence of unfitted nuclear density (negative for H2O treated samples, and positive for D2O treated samples) adjacent to the O3 and O4 sites, giving sensible O-H/D distances. The results therefore indicate more than one proton site, consistent with modelling studies which suggested that there was little difference between the proton defect energies for different oxygen sites. The results indicate a mixture of inter- and intra-tetrahedra H bonding interactions, with the shortest interaction being of the order of 2 Å. Further modelling studies into dopant site selectivity are also reported which indicate that charge and size effects dominate the solution energies.