Subsolidus phase equilibria and magnetic characterization of the pyrochlore in the Bi2O3-Fe2O3-Sb2Ox system

The subsolidus phase equilibria of the Bi2O3-Fe2O3-Sb2Ox system have been investigated by X-ray powder diffraction. The isothermal section of the system at 775-800 °C has been constructed. It can be represented by 9 phase assemblage triangles. Ternary compound formation is limited to pyrochlore which forms a substantial solid solution region of Bi-deficient compositions relative to Bi2FeSbO7. As follows from the phase diagram, approximately 7-25% of Bi positions in pyrochlore may be occupied with Fe3+ ions that was confirmed by Mossbauer data. Magnetic measurements were carried out on the pyrochlore specimen of quasi-chemical formula (Bi1.8Fe0.2)(FeSb)O7. The existence of the strong short-range antiferromagnetic superexchange interactions and spin-glass magnetic transition at around 9 K were revealed.