Site occupancy of rare-earth cations in BaTiO3

A systematic study on the site occupancy of rare-earth cations in Ba-rich a nd Ti-rich BaTiO3 fired in reducing atmosphere is performed. The correspond ing lattice relaxation is used as an indicator of site occupancy and, to a lesser extent, defect structures. Accurate lattice parameters are obtained from X-ray diffraction data that is analyzed with the maximum likelihood me thod to account for correlated errors in the c and a lattice parameters. Co mparisons of lattice volume as a function of ionic radius of the dopant rev eals three regimes, with the intermediate sized cations (0.087 nm less than or equal to r less than or equal to 0.094 nm where r is the ionic radius i n six-fold coordination) demonstrating amphoteric behavior (occupying A- or B-sites). Defect chemistry analysis of site occupancy links the importance of metal vacancy ratios and oxygen vacancy concentrations with site occupa ncy. The trends predicted from the defect chemistry analysis are consistent with the observed lattice relaxations.