Distribution of Mn3+ and Mn4+ species between octahedral and square pyramidal sites in Bi2Mn4O10-type structure

Abstract

The cationic distribution in the iron substituted manganites Bi ₂ Mn _{4– x} Fe _x O ₁₀ (0≤x≤1) has been investigated combining X-ray powder diffraction (XRPD), magnetic susceptibility measurements and ⁵⁷ Fe Mössbauer spectroscopy. Iron is at the trivalent state and exhibits, like Mn ³⁺ the high spin configuration. It is shown that Fe ³⁺ is distributed over the two sites of the structure, octahedral and square pyramidal, with a preferential occupation of the second one. Consideration of the Mn(Fe)-O distances leads, for x=1, to the cationic distribution Bi ₂ [Mn _1.66 ⁴⁺ Fe _0.34 ³⁺ ] _O [Mn _1.00 ³⁺ Mn _0.34 ⁴⁺ Fe _0.66 ³⁺ ] _P O ₁₀ , showing that Mn ⁴⁺ is also susceptible to sit in the pyramidal site. Magnetic and structural study of the oxides Bi ₂ Mn _{4– x} Ti _x O ₁₀ (0≤x≤1) and Bi ₂ Mn _3.75 Al _0.25 O ₁₀ suggests that Ti ⁴⁺ and Al ³⁺ respectively sit in the octahedral and square pyramidal sites of the structure according to the formulae Bi ₂ [Mn _{2– x} ⁴⁺ Ti _x ⁴⁺ ] _O [Mn ₂ ³⁺ ] _P O ₁₀ and Bi ₂ [Mn ₂ ⁴⁺ ] _O [Mn _1.75 ³⁺ Al _0.25 ³⁺ ] _P O ₁₀ .