Subsolidus phase equilibria in the La2O3–Fe2O3–Sb2O5 system and characterization of layered ternary oxide LaFe0.5Sb1.5O6

Phase equilibria in the La2O3-Fe2O3–Sb2O5 system have been studied. The isothermal section was constructed at T=900 °С. The existence of the ternary oxide LaFe0.5Sb1.5O6 was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe0.5Sb1.5O6 crystallizes in a trigonal layered structure relating to PbSb2O6 type (space group P-31m, a=b=5.2446(3) Å, c=5.1930(3) Å, Z=1). The fine powder of LaFe0.5Sb1.5O6 was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe0.5Sb1.5O6 in the applied magnetic field H=5000 Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100 Oe the magnetic data of LaFe0.5Sb1.5O6 indicates an unusual critical behavior near phase transition at T<2 K.