First-principles study of Ca2+ and Mn2+ substituents in KTaO3 - art. no. 134415

The structural properties, energetics, and dynamics of Ca2+ and Mn2+ substi tuents in KTaO3 are investigated from first principles. It is found that Ca substitutes for both K and Ta ions. Oxygen vacancies bind to isolated Ca i ons residing at Ta sites, causing off-center Ca displacement and forming la rge dipoles. There is also evidence that oppositely charged defects may clu ster together. Our calculations predict that the activation energy for dipo le reorientation via oxygen vacancy hopping within the first-neighbor shell of Ta-substituting Ca or. Mn exceeds 2 eV. On the other hand, Mn2+ substit uting at the K site displaces off center along the (100) direction, also fo rming a dipole. This dipole can reorient via Mn hopping motion with an acti vation energy of similar to0.18 eV, in reasonable agreement with experiment s. We argue that, in general, metal ion hopping at the A site, not oxygen v acancy hopping, is responsible for the small activation energies found in e xperiments.