Isomer shift and quadrupolar splitting of the Mössbauer spectrum of ferroelectrics

The parameters of the Mössbauer spectrum of Fe 3+ ions in ferroelectrics are considered. It is shown that the internal electric fields in ferroelectrics cause the strong polarization of the—covalency occupied 4s shell of Fe 3+ . This gives the significant contribution to the isomer shift and quadrupolar splitting of the Mössbauer spectrum. For BaTiO 3 , this contribution determines both sign and magnitude of the observed discontinuous change of the shift at T c . It is also shown that the structure reconstruction of BaTiO 3 decreases the isomer shift at the transition in the ferroelectric phase. The contribution of the electrically polarized 4s shell of Fe 3+ ion to the quadrupolar splitting of the Mössbauer spectrum for BaTiO 3 gives more than a half of the observed value of the quadrupolar splitting.