Solid state miscibility in the pseudo-binary TiO2 - (FeSb)O4 system at 1373 K

The tetragonal rutile-type (FeSb)O4 compound was synthesized reacting Fe2O3 and Sb2O3 in O2. Solid solubility in the pseudo-binary TiO2-(FeSb)O4 (rutile - tripuhyite) system was investigated annealing powder mixtures characterized by different TiO2(FeSb)O4 molar ratios in an O2 flux. Complete miscibility was found in the whole compositional range at 1373 K. The crystal structures of (FeSb)O4 and selected terms of the (Ti2xFe1-xSb1-x)O4 solid solution (0 <= x <= 1) were refined from X-ray powder diffraction data using the Rietveld method. Selective broadening of the X-ray lines was observed and analyzed by means of the Gaussian quadratic plot. Line broadening is probably related to a phase transformation taking place at low temperature, as suggested by the excess molar volume of the solid solution. As a result local chemical inhomogeneity and microstrain in the direction perpendicular to the 00l lattice planes for compositions 0.2 <= x <= 0.6 are generated.