Abstract—
Using high-pressure, high-temperature processing of a low water content amorphous tantalum hydroxide, TaO0.5–2.0(OH)4–1 · (1.0–2.5)H2O, at p = 5.0–6.0 GPa and t = 800–900°C, we have obtained a mixture of two phases, Ta2O5 · 2/3H2O (sp. gr. P63/mсm, а = 7.4736(2) Å, с = 7.6798(2) Å, Z = 3, V = 371.48(1) Å3) and H2Ta2O6 · 2/3H2O (sp. gr. P63/mсm, а = 7.4998(2) Å, с = 7.6171(2) Å, Z = 3, V = 371.04(1) Å3), both crystallizing in the hexagonal tungsten bronze (HTB) structure. According to thermogravimetric analysis results, the material contains 4.9(3)% water. After water removal, heating in air to 550°C causes the HTB phase to convert into δ-Ta2O5. X-ray diffraction data have been analyzed by the Rietveld method and the following reliability factors have been obtained: RF = 0.0374 for Ta2O5 · 2/3H2O and RF = 0.0416 for H2Ta2O6 · 2/3H2O. We assume that the MO3 stoichiometry of the basic HTB cell in these compounds is ensured by different mechanisms.
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ACKNOWLEDGMENTS
This work was supported by the Russian Foundation for Basic Research, project no. 16-03-00171 a.
The transmission electron microscopic work was carried out using equipment at the Shared Characterization Facilities Center, Omsk Scientific Center, Siberian Branch, Russian Academy of Sciences.
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Zibrov, I.P., Filonenko, V.P., Trenikhin, M.V. et al. High-Pressure Synthesis of H2 –xTa2O6 – 0.5x · 2/3H2O (0 ≤ x ≤ 2) with the Hexagonal Tungsten Bronze Structure. Inorg Mater 55, 489–494 (2019). https://doi.org/10.1134/S0020168519040174
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DOI: https://doi.org/10.1134/S0020168519040174