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Structural and microstructural changes in the zirconium–indium mixed oxide system during the thermal treatment

The zirconium–indium mixed oxide systems on both the zirconium- and the indium-rich side of the concentration range were prepared by co-precipitation from aqueous solutions of the corresponding salts, followed by washing and heat-treatment. The thermal behavior (up to 1000 °C) of the dried samples was examined by X-ray powder diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectrometry, differential thermal analysis and thermogravimetric measurements. The obtained results show that the increase in the amount of the second phase causes an increase of both the crystallization temperature of the amorphous precursors of ZrO2, from 435 °C (0 mol.% of InO1.5) to 476 °C (not, vert, similar62 mol.% of InO1.5), and of the topotactic transition temperature of cubic In(OH)3 to cubic In2O3, from 259 °C (0 mol.% of ZrO2) to 290 °C (not, vert, similar25 mol.% of ZrO2). The amorphous precursors of ZrO2 phase exhibit an extended capability to incorporate In3+ ions (more than 60 mol.%). With a rise in temperature the maximum solubility of In3+ ions in the ZrO2 lattice decreases from not, vert, similar55 mol.% in the crystallization products obtained after calcination at 400 °C to not, vert, similar10 mol.% after calcination at 1000 °C. The results of phase analysis indicate that the incorporation of In3+ ions partially stabilized both the tetragonal and cubic ZrO2 polymorphs. The maximum solubility of Zr4+ ions in the starting In(OH)3 lattice was estimated at not, vert, similar10 mol.%. Thermal treatment causes a small increase of Zr4+ ion solubility limits, estimated at not, vert, similar15 mol.% in the cubic In2O3 lattice after calcination at 1000 °C. Precise lattice parameter measurements, by using Le Bail refinements of the powder diffraction patterns with added silicon as an internal standard, show that the incorporation of In3+ ions caused a very small decrease of the cubic ZrO2 lattice, while the incorporation of Zr4+ ions had a negligible influence on the parameters of cubic In(OH)3 and In2O3 lattices. The obtained results were compared with the results obtained for mixed oxides of zirconium and undersized trivalent metals (systems ZrO2–Fe2O3, ZrO2–Ga2O3, ZrO2–Cr2O3 and ZrO2–Al2O3).

ZrO2 ; In2O3 ; X-ray diffraction ; Raman spectroscopy ; electron microscopy ; DTA

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