A. Ducouret

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

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 Mossbauer 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 .

Neutron diffraction and Mössbauer spectroscopy studies of the mixed valent T1-1212 ferrite (Tl0.5Pb0.5)Sr3Fe2O8

Abstract The mixed valent 1212-ferrite (Tl0.5Pb0.5)Sr3Fe2O8 has been characterized using powder neutron diffraction data collected at 1.5 and 293 K. The structure is confirmed to be close to that of the Tl-1212 superconductor (Tl0.5Pb0.5)Sr2CaCu2O7 but with no deviation from a full occupancy of (Tl,Pb) and oxygen sites. 57Fe-Mossbauer spectroscopy data depend upon the temperature between 4.2 and 293 K. They have been explained on the basis of a mixture of trivalent and tetravalent iron states at 4.2 and 150 K. At temperature higher than 150 K the existence of intermediate iron states Fen+ (3