Mossbauer investigation of Fe-57-doped Ni(III) perovskites ANi(0.98)Fe(0.02)O(3) (A = Pr, Nd, Sm, Y, Lu, Tl) versus temperature

摘要

Nickelates ANiO(3) (A = Pr, Nd, Sm, Lu, Y, Tl) containing Mossbauer probe Fe-57 atoms were synthesized. In the case of nickelates with larger rare earth (A = Pr, Nd, Sm) the Mossbauer spectra confirm that ferric ions are located in single type of crystallographic positions. On the contrary, the spectra of ANi(0.98)Fe(0.02)O(3) with small cations (A = Lu, Y, Tl) can be described as a superposition of two sub-spectra which indicate that 57Fe probe atoms are simultaneously stabilized in two non-equivalent crystallographic positions. These results have been interpreted in terms of partial charge disproportionation of Ni3+ cations associated with the electronic localization in monoclinic distorted Lu, Y, Tl nickelates. The modification of 57 Fe spectra for TlNi0.98Fe0.02O3 as a function of temperature has shown that this charge disproportionation occurs in varying degrees, corresponding to the charge states Fe(3+sigma)+ and Fe(3-sigma')+. On the contrary, the spectra for Lu and Y nickelates show that charge variation (sigma, sigma') for dopant Fe(1) and Fe(2) cations does not depend on temperature. (C) 2002 Elsevier Science (USA). [References: 15]