Electronic state of 57Fe Mössbauer probe atoms in Cu(III) oxides with perovskite and perovskite-related structures

Mössbauer spectroscopy studies were developed in order to obtain an evaluation of different physico-chemical factors characterizing the electronic structure of the local sites (CuO6) into three copper(III) oxides: LaCuO3 having a three-dimensional (3D) perovskite structure; SrLaCuO4 and La2Li0.50Cu0.50O4 with a two-dimensional (2D) K2NiF4-type structure. All these matrixes have been doped with 57Fe (1 at.%) Mössbauer probe atoms. Such evaluation was based on analysis of the 57Fe Mössbauer parameters (isomer shift and quadrupole splitting) characterizing the formal oxidation state and the local structure of the 57Fe probe atoms. The obtained results underline that four main factors play an important role in the stabilization of formally trivalent “Cu3+” ions: (i) the involved preparation process (in particular the oxygen pressure level able to impede the formation of oxygen vacancies); (ii) the dimensionality (3D or 2D) of the lattice; (iii) the chemical surrounding and (iv) the local structural distortion of the transition metal site (CuO6), both last factors governing the local crystal field energy, orbital ordering and a possible charge transfer Cu3+-O2− ↔ Cu2+-O−(L).