New complex bismuth oxides in the Bi2O3–NiO–Sb2O5 system and their properties

• We have constructed the isothermal section of the system Bi2O3–NiO–Sb2O5.
• The boundaries of pyrochlore structure solid solution have been determined.
• New Bi3Ni2/3Sb7/3O11 compound of KSbO3 structure type have been discovered.
• The structures were studied by means of synchrotron X-ray diffraction and XAFS.
• Magnetic measurements revealed that both compounds are paramagnetic at 2–350 K.

Phase equilibria in the Bi2O3–NiO–Sb2O5 system have been investigated. The isothermal section of the system (650°) has been constructed. For the first time the existence of the pyrochlore structure solid solution, (Bi2−xNix)Ni2/3−ySb4/3+yO7±δ, x=0.1−0.35, y=0−0.1, and a new compound Bi3Ni2/3Sb7/3O11 of KSbO3 structure type have been discovered. The structures and properties of these compounds were studied by XRD, XAFS, diffuse reflection spectroscopy and magnetic methods. Rietveld refinement of synchrotron radiation-based powder XRD data for pyrochlore sample of 38.43Bi2O3–33.0NiO–28.57Sb2O5 composition and Bi3Ni2/3Sb7/3O11 compound was performed. The best possible refinement of the positional parameters for both pyrochlore and Bi3Ni2/3Sb7/3O11 structures was achieved for disordered models. Magnetic, diffuse reflection and an X-ray absorption spectroscopy study confirmed that in both compounds nickel ions are mainly in a 2+ oxidation state. According to magnetic data, Bi1.84Ni0.16(Ni0.63Sb1.37)O7 pyrochlore and Bi3Ni2/3Sb7/3O11 are overall paramagnetic in nature.

Isothermal section of the Bi2O3–NiO–Sb2O5 system at 650 °C in air and variation of magnetic susceptibility and inverse susceptibility with temperature for Bi1.84Ni0.79Sb1.37O7 pyrochlore.Figure optionsDownload as PowerPoint slide