Synthesis, magnetic properties and Mössbauer spectroscopy for the pyrochlore family Bi2BB'O7 with B=Cr and Fe and B?=Nb, Ta and Sb

M. C. BLANCO; D. G. FRANCO; Y. JALIT; E. V. PANNUNZIO MINER; G. BERNDT; A, PAESANO JR; G. NIEVA; R. E. CARBONIO

Conferencia; At the Frontiers of Condensed Matter V; 2010

The samples Bi2BB´O7, with B = Cr and Fe and B´= Nb, Ta and Sb were prepared by solid state method. The crystallographic structure was investigated on the basis of X-ray powder diffraction data. Rietveld refinements show that the crystal structure is cubic, space group Fd-3m. The Bi3+ cation on the eight-coordinate pyrochlore A-site shows displacive disorder, as a consequence of its lone pair electron configuration. There is also a considerable A-site disorder shown by Rietveld Analysis and confirmed in the case of the iron containing samples with M¨ossbauer spectroscopy. The magnetic measurements show paramagnetic behavior at all temperatures for the Cr oxides. The Fe pyrochlores show antiferro-magnetic order around 10K.