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Pyrochlore Range from Bi2O3–Fe2O3–TeO3 System for LTCC and Photocatalysis and the Crystal Structure of New Bi3(Fe0.56Te0.44)3O11

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Author to whom correspondence should be addressed. e-mail: matjaz.valant@ung.si.

Abstract

A new pyrochlore homogeneity field in Bi2O3–Fe2O3–TeO3 system is characterized with respect to its compositional range and phase relations to adjacent phases. The sintering temperature of these pyrochlores is 880°C and they do not react with metallic silver, which makes them suitable for low-temperature cofired ceramics (LTCC) technology. Magnetic measurements indicate a spin-glass formation. The spin freezing temperature that occurs at around 20 K shows a slight, yet systematic, variation with the sample composition. The dielectric constant increases with an increase in Bi content from 37(1) to 55(1). At cryogenic temperatures, they show the dielectric relaxation typical for displacive pyrochlores. The UV–Vis diffuse reflectance data were used for calculation of the electronic band gap. The lowest band gap was determined to be 1.965 eV. Next to the pyrochlore range, another new phase was discovered. Structural analysis showed that Bi3(Fe0.56Te0.44)3O11 crystallizes as KSbO3-type in a displacive disordered cubic inline image symmetry with a lattice parameter of 9.47045(15) Å.

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