P. Millet et al., Syntheses, crystal structures and magnetic properties of francisite compounds Cu3Bi(SeO3)(2)O2X (X = Cl, Br and I), J MAT CHEM, 11(4), 2001, pp. 1152-1157
Synthetic analogues of francisite, a mineral of complex formula Cu3Bi(SeO3)
(2)O2X with X = Cl, Br, I, have been obtained by solid state reaction. Cont
rary to the previous structure description, the framework can be better des
cribed as formed of copper(II)-oxygen layers linked together in the [001] d
irection by long bismuth-oxygen bonds. These layers are formed by a hexagon
al network of [CuO4] square plane sharing apices whose geometry is reminisc
ent of a Kagome type lattice. Preliminary magnetic susceptibility measureme
nts performed on the X = Cl and Br compounds have revealed ferromagnetic-li
ke behaviour below T-c approximate to 24 K. Linear birefringence and X-band
Electron Spin Resonance (ESR) data are also presented.