Abstract
Using high-pressure heat treatment of amorphous low-hydrated tantalum hydroxide of composition TaO0.5–2.0(OH)4–1 · 1.0–2.5H2O at p = 5.0 GPa and t = 600–750°C, we obtained a mixture of two phases: H2Ta2O6 · H2O with a defect pyrochlore structure (sp. gr. Fd3m, a = 10.5956(1) A, Z = 8, V = 1189.53(3) A3) and TT-Ta2O5 (δ) (α-UO3 structure, sp. gr. P3 m1, a = 3.6368(2) A, c = 3.8943(5) A, Z = 1, V = 44.61 A3). The X-ray diffraction data for these compounds were analyzed by the Rietveld method. The agreement factors obtained are RF = 0.0541 for H2Ta2O6 · H2O and RF = 0.0885 for TT-Ta2O5. These phases are assumed to form an intergrowth structure along certain crystallographic planes. We have proposed a mechanism of intergrowth structure formation in the [111] direction of the pyrochlore structure and in the [001] direction of TT-Ta2O5.
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