The application of a new potential model to the rare-earth doping of SrTiO3 and CaTiO3

We have performed a computational study on the rare-earth (RE) doping of the perovskite structured materials; SrTiO3 and CaTiO3. The calculations have been completed using new Sr-O and Ca-O potentials in combination with a recently developed set of interatomic potentials, previously fitted and tested on polymorphs of BaTiO3. Particular attention has been given to the energetic and structural consequences of rare-earth doping via the five major dopant incorporation schemes. For SrTiO3, large RE ions dope at the Sr-site via a Sr vacancy mechanism, whereas smaller RE ions prefer doping via self-compensation due to the size of the ions being approximately half way between the size of the larger Sr-site and smaller Ti-site. Our simulations show that for CaTiO3, large to mid-sized RE ions (La to Eu) energetically favour Ca-site doping with Ca vacancy charge compensation and smaller ions dope via self-compensation. On comparison with previous calculations for BaTiO3, our results show the effect of the A-site size decrease from Ba to Ca on the favoured incorporation mechanism. The results for both materials are in good agreement with experiment. An overall assessment of the RE-doping in this perovskite series (ATiO(3), where A = Ba, Sr or Ca) is given.