Atomistic simulation studies of trapped hole bipolarons in BaTiO₃

Abstract

Classical shell-model-and embedded-cluster-rype cdculuians are employed in order to supply thearetical arguments in favour of hale bipolarons in BaTiOx which have recently been speculated to exist in this photorefractive material. Our investigations concern the geometrical structure of hole bipolaram trapped at acceptor defects, their spin state and hole ionization energies. In particular the embedded-cluster modelling studies, which explicitly include the local electronic defect strncture. suggest the importance of lattice relaxation and electron correlation terms in order to stabilize diamosetic 0:-molecules (bipolaram) in BaTiO3. Our simulations show that hole bipalnrans arc predominantly bound at Ti-site acceptor defects. A trapping of bipolarons at Ba-site acceptors is in most cases unfavourable. Finally. by extrapolating OUT present results to the high-T, superconducting oxides we qualitatively discuss the possible r6le of small hole (perouy) bipolamns in these materials.

Interconversion of intrinsic defects in SrTiO3(001)

“…We find that V Sr does not result in occupied gap states. However, our calculations show that O int 2--, a largely unexplored candidate defect [50], does. We previously found that O 2 is readily absorbed when epitaxial films of NdTiO 3 are exposed to air, and that it most likely resides in interstitial sites [51].…”

Semi-Empirical Calculations of Hole Polarons in MgO and KNbO3 Crystals

“…(iii) Of great interest are detailed ab initio polaron simulations which would include the electron correlation effects (cf. [21]). This could give more confidence to the pre- Fig.…”

Ab initiostudy of oxygen vacancies in BaTiO3

“…The modelling of the embedding lattice and of cluster-lattice interactions employs a shellmodel pair-potential description (see also references [18][19][20]). The shell-model parameters have been taken from the earlier work of Lewis and Catlow [2].…”