Characteristics and local structure of hafnia-silicate-zirconate ceramic nanomixtures.
Zirconate systems having the composition 3HfO2·15SiO2·xY2O3·(82 - x)ZrO2, where x = 2, 7 and 12 mol% Y2O3, were synthesized by a sol-gel method. The analysis of X-ray diffraction data showed the presence of the t-ZrO2, m-ZrO2, m-HfO2, Y2SiO5 and Y2Si2O7 crystalline phases in a ceramic nanomixture. Spectroscopic data show that the increase of the Y2O3 content of samples determines the increase of the t-ZrO2, m-HfO2 and silicate crystalline phases. Gap energy values decrease almost linearly with increasing Y2O3 content of samples. A detailed study of XANES data does not show a significant difference with increasing Y2O3 content of the samples suggesting an appreciable stability of the hafnium ions +4 oxidation state and their microvicinity. EXAFS results show that the local structure around the Hf cation is similar to that from the monoclinic crystalline HfO2 where the Hf-O coordination number tends to 7. The bond lengths of Hf-O shells show small deviations from ∼2.12 Å and the Hf-metal paths become more structured by increasing the Y2O3 content of the samples.
['Pop|L|L|', 'Rada|S|S|', 'An|P|P|', 'Zhang|J|J|', 'Rada|M|M|', 'Suciu|R C|RC|', 'Culea|E|E|']
composites sol-gel sol-gel method XANES EXAFS. XAS hafnia–silicate–zirconate nanostructure spectroscopy