Synthesis, structure, and magnetic properties of the layered bismuth transition metal oxide solid solution Bi sub 2 Fe sub 4 minus x Ga sub x O sub 9

The solid solution Bi{sub 2}Fe{sub 4{minus}x}Ga{sub x}O{sub 9} (0 {le} x {le} 4) was synthesized and investigated by X-ray diffraction, Moessbauer spectroscopy, and susceptibility measurements. The system was found essentially to follow Vegard's law. The crystal structure of the x = 2 member, Bi{sub 2}Fe{sub 2}Ga{sub 2}O{sub 9}, was solved. The structure is orthorhombic with space group Pbam (No. 55), a = 7.946(1) {angstrom}, b = 8.355(1){angstrom}, and c = 5.929(1) {angstrom}. Iron and gallium were nonstatistically distributed over two octahedral and two tetrahedral sites. The iron displayed a 60% preference for the octahedral positions. Magnetic susceptibility and Moessbauer measurements showed antiferromagnetic behavior. The ordering temperature, T{sub N}, exhibited a strong dependence on x, decreasing rapidly with gallium doping from T{sub N} = 245 {plus minus} 5 K for x = 0 to T{sub N} {lt} 4.2 K for x = 3. Spin-glass-like behavior was observed in the gallium-substituted compounds, and a previously undetected spin rearrangement at 220 K for the x = 0 compound is reported.