Structures and phase transitions of B-Ta2O5 and Z-­Ta2O5: two high-pressure forms of Ta2O5

• Published in: Acta crystallographica. Section B, Structural science Vol. 56; no. 4; pp. 659 - 665
• Main Authors: Zibrov, I. P., Filonenko, V. P., Sundberg, M., Werner, P.-E.
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.08.2000
• Subjects: High-pressure forms; Microscopy, Electron; Models, Molecular; Molecular Structure; Oxides - chemistry; Phase Transition; Phase transitions; Powder Diffraction; Pressure; Sensitivity and Specificity; Structure; Tantalum - chemistry
• ISSN: 0108-7681; 1600-5740
• DOI: 10.1107/S0108768100005462

A sample of Ta2O5, ditantalum pentaoxide, heat‐treated in a `toroid'‐type high‐pressure chamber at P = 8 GPa and T = 1470 K, was studied by X‐ray powder diffraction and high‐resolution transmission electron microscopy (HRTEM). Two high‐pressure modifications of Ta2O5, isostructural with B‐Nb2O5 and Z‐Nb2O5, were identified from the X‐ray powder pattern. Both structures were refined by the Rietveld method from the X‐ray diffraction data: B‐Ta2O5, a = 12.7853 (4), b = 4.8537 (1), c = 5.5276 (2) Å, β = 104.264 (2)°, V = 332.45 Å3, Z = 4, space group C2/c; Z‐Ta2O5, a = 5.2252 (1), b = 4.6991 (1), c = 5.8534 (1) Å, β = 108.200 (2)°, V = 136.53 Å3, Z = 2, space group C2. The Z‐Ta2O5 modification is new. The Ta atoms are six‐coordinated in B‐Ta2O5 and seven‐coordinated in Z‐Ta2O5. The two structures are closely related, which makes an intergrowth and a transformation between them possible. An idealized model of the intergrowth structure has been given. The HRTEM study showed defect‐rich B‐Ta2O5 crystals, which could be interpreted as an intergrowth between the B‐­Ta2O5 and Z‐Ta2O5 phases.