The crystal structure of the high temperature form of Ta2O5

New Calcium Tantalate Polytypes in the System Ca2Ta2O7–Sm2Ti2O7

“…The tantala polymorphs have been described in terms of corner-and edge-linked pentagonal bipyramids and octahedra (18,19). However, a pentagonal bipyramid sharing two adjacent equatorial edges with octahedra is topologically equivalent to a triangular group of corner-shared octahedra.…”

The structure of niobium and tantalum oxides processed by concentrated light flux

“…The β-modification of Та 2 О 5 is stable up to 1360°С. This phase looks like colourless rhombic crystals (z = 11) of the space group P2mm, with the melting point 1787°С and the density 8.18 g/cm 3 [5,6,12]. The α-modification of Та 2 О 5 is stable above 1560°С and looks like grey tetragonal crystals (z = 6) of the space group I4 1 /amd (the melting point being 1887°С and the density 8.37 g/cm 3 ).…”

“…In particular, the both modifications have the same structural units. They contain ТаО 6 octahedrons and distorted pentagonal ТаО 7 bi-pyramids, forming a three-dimensional framework of bonds of a different type [12][13][14][15]. Obviously, the ceramic samples contain different modifications of Nb 2 O 5 and Та 2 O 5 that belong to different crystalline systems.…”

Thermal expansion of specimens of niobium and tantalum pentoxides obtained by melting in an optical furnace

“…Melted specimens of Ta 2 O 5 had a rhombic phase (a = = 4.3998 nm, b = 0.3894 nm, c = 0.6209 nm, space group Pmm2 [2]) and also contained 15 -20% monoclinic phase (a = 0.3810 nm, b = 0.3810 nm, c = 0.3810 nm, c = = 3.5764 nm, b = 90°, space group I2 [13]). Therefore we may speak of possible partial hardening of the high-temperature monoclinic Ta 2 O 5 phase due to rapid cooling in the focal zone of the optical furnace.…”