The crystal structure of synthetic natrotantite

Abstract

Ideal natrotantite has the composition Na2Ta4O11, space group R-3c, a = 6.2092(1), c = 36.619(1) Å, Z = 6. The structure of synthetic natrotantite has been refined by the Rietveld method to Rp = 8.67, Rwp = 9.24, RB = 2.33 % using X-ray powder diffractometer data. The structure consists of layers of (l) edge-sharing NaO7 polyhedra and TaO7 octahedra and (2) edge-sharing TaO7 pentagonal bipyramids, alternating along Z. Natrotantite is topologically identical to, but not isomorphous with Na2Nb4O11 ; the Na2Nb4O11 structure is a monoclinic distortion of the natrotantite structure. The structure is also similar to that of calciotantite from which it differs in its layer (l) topology and in its layer stacking. Natural natrotantites are typically non-stoichiometric ; Na2-xTa4O11-x(OH,F)x is proposed as a more realistic formula for the mineral.

Synthesis and Optical Properties of Ag(I), Pb(II), and Bi(III) Tantalate-Based Photocatalysts

“…The A 2 Ta 4 O 11 (A = Na, Ag) structures consist of layers of edge-sharing TaO 7 pentagonal bipyramids alternating with layers of TaO 6 octahedra surrounded by 7-coordinate Na(I) cations or 6-coordinate Ag(I) cations, as described previously. 12,15,18,37 The layer containing isolated TaO 6 octahedra is connected to the adjacent layers via corner sharing of the apical oxygens of the TaO 7 pentagonal bipyramids and are stacked down the c-axis, as shown in Figure 2. PbTa 4 O 11 is structurally similar to the A 2 Ta 4 O 11 phases, with the Pb(II) cations surrounding the isolated TaO 6 octahedra that alternate with the TaO 7 pentagonal bipyramid layers.…”

Structural characterization of Pu-bearing murataite ceramic

“…containing murataite modules in their structure are considered as murataite polytypes. The murataite structure contains four distinct cation sites capable to accommodate variable size cations [6]. Suitability of the murataite-based ceramics as potential nuclear waste forms was also confirmed by their good radiation resistance [7,8].…”

Dielectric properties, polymorphism, structural characterisation and phase diagram of Na2Nb4O11–Ag2Nb4O11 solid solutions

“…Lattice parameters (a, b and c in Å; β in degrees) and unit cell volume (V in Å 3 ) from XRD data at room temperature vs x for (Na 1 À x Ag x ) 2 Nb 4 O 11 . The lattice parameters of the hexagonal-R unit cell for x 40.8 are redefined on monoclinic axes [16]. Error bars are smaller than actual symbols.…”

“…The lattice parameters of the hexagonal-R unit cell above $ 340 K are redefined on monoclinic axes[16]. Error bars are smaller than actual symbols.…”