Two new Sr-rich layered manganites with a 1:1 Bi-Sr ordering:: 1201 Bi0.4Sr2.6MnO5-δ and 2201 Bi0.9Sr3.1MnO6-δ

Two new strontium-rich manganites with a layered structure, Bi0.4Sr2.6MnO5-delta and Bi0.9Sr3.1MnO6-delta, have been synthesized and characterized, using X-ray powder diffraction and electron microscopy. The first, Bi0.4Sr2.6MnO5-delta, crystallizes in the space group I4/mmm with a = 5.3756(1) Angstrom and c = 35.578(1) Angstrom and shows for the first time the possibility to stabilize a manganite with a 1201-type structure. The second, Bi0.9Sr3.1MnO6-delta, which crystallizes in the P2(1) space group with a = 5.2829(2) Angstrom, b = 5.2998(2) Angstrom, c = 23.9906(6) Angstrom, and gamma = 90.27(2)degrees, exhibits a 2201 unmodulated structure. Both oxides are characterized by a 1:1 ordering between bismuth and strontium forming rows parallel to (b) over right arrow, while a quadrupling of the c parameter is observed in the case of the 1201 structure. The investigation of their magnetic properties shows a complex magnetic behavior connected to the existence of trivalent manganese in MnO2 planes. (C) 2000 Academic Press.