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 Bi₂Mn_4–xFe_xO₁₀ (0≤x≤1) has been investigated combining X-ray powder diffraction (XRPD), magnetic susceptibility measurements and ⁵⁷Fe Mössbauer spectroscopy. Iron is at the trivalent state and exhibits, like Mn³⁺ the high spin configuration. It is shown that Fe³⁺ 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 Bi₂[Mn_1.66⁴⁺Fe_0.34³⁺]_O[Mn_1.00³⁺Mn_0.34⁴⁺Fe_0.66³⁺]_P O₁₀, showing that Mn⁴⁺ is also susceptible to sit in the pyramidal site. Magnetic and structural study of the oxides Bi₂Mn_4–xTi_xO₁₀ (0≤x≤1) and Bi₂Mn_3.75Al_0.25O₁₀ suggests that Ti⁴⁺ and Al³⁺ respectively sit in the octahedral and square pyramidal sites of the structure according to the formulae Bi₂[Mn_2–x⁴⁺Ti_x⁴⁺]_O[Mn₂³⁺]_P O₁₀ and Bi₂[Mn₂⁴⁺]_O[Mn_1.75³⁺Al_0.25³⁺]_P O₁₀.

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