Polaronic deformation at theFe2+/3+impurity site inFe:LiNbO3crystals

Abstract

Iron doped LiNbO 3 crystals with different iron valence states are investigated. An extended x-ray absorption fine structure (EXAFS) spectroscopy study highlights evident changes in the local structure around iron that can be ascribed to the presence of small polarons. In particular, when a Fe 3+ replaced a Li ion, the oxygen octahedron shrinked with respect to the pure material, with an average iron-oxygen bond value very similar to that of Fe 2 O 3 hematite. When adding an electron, it localizes at the Fe site in a configuration very close to the atomic Fe d orbitals, inducing a relaxation of the oxygen cage. The same system was modelled by spin-polarized density functional theory (DFT). Several local as well as hybrid exchange-correlation functionals were probed on the bulk LiNbO 3 structural properties. The computation is then extended to the case of hematite and finally to the Fe defect in LiNbO 3. The calculations reproduced with good accuracy the large lattice relaxation of the oxygen ligands associated to the electronic capture at the Fe center that can be interpreted as due to the polaron formation. The calculations reproduce satisfactorily the available EXAFS data, and allow for the estimation of the polaron energies and the optical properties of the defect.

Atomic insight to lattice distortions caused by carrier self-trapping in oxide materials

“…4). Considering this scaling our calculations are consistent with recent ab initio studies of the polaronic deformation at the impurity site in Fe:LiNbO 3 by Sanson et al 39. who found a ≈4.7% decrease of the Fe-O distance ( nm) upon hole capture by Fe 2+ , thus, supporting our model assumptions.…”

Local structure and spin transition inFe2O3hematite at high pressure

“…The validity of this assumption was tested in Ref. [27] and is also confirmed by the subsequent agreement with the crystallographic data of hematite. The same assumption was made for the analysis of the next-nearest-neighbor Fe-Fe/O distances.…”

Bound electron polarons in lithium niobate

“…Several local and semilocal exchange-correlation functionals have been tested as described in Ref. [13]. Due to the overall satisfactory agreement with the experimental results and the moderate computational cost, the semi-local form proposed by Perdew and Wang (PW91 [14]) of the generalized gradient approximation (GGA) is employed in this work.…”