Ilmenite-type Na2(Fe2/3Te4/3)O6

Na2(Fe2/3Te4/3)O6 was obtained under hydrothermal conditions and adopts the ilmenite (FeTiO3) structure type.


Structure description
Crystals of Na 2 (Fe 2/3 Te 4/3 )O 6 were inadvertently obtained during hydrothermal synthesis attempts originally aiming at a phase with composition Na 12 Fe III 6 Te VI 4 O 27 •3H 2 O and for which possible relationships with the potassium phase K 12 Fe III 6 Te VI 4 O 27 •3H 2 O (Eder, 2023) were to be investigated.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.
All crystals under investigation were systematically twinned with at least two twin domains present.During the integrating and scaling process of the finally chosen crystal, a pseudo-Laue class of 3.m was suggested by X-AREA (Stoe, 2021) with similar R int values compared to the Laue class corresponding to the actual structure (3).From this pseudo-symmetry imposed by the twinning, one possible twin law (m ( 210) ) with a transformation of a, À aÀ b, c was derived.The intensity data were integrated on basis of a hexagonal primitive unit-cell of same dimensions to include the reflections of both twin domains (Fig. 3).By applying the twin law given above, the ratios of the respective domains refined to values of 0.540:0.460(2).For the sake of charge-neutrality, the mixedoccupied (Fe III /Te VI ) site was constrained to a ratio of 1:2 for Fe:Te.The two atom types located at this site were refined with common displacement parameters.

Figure 1
Figure 1 Crystal structure of ilmenite-type Na 2 (Fe 2/3 Te 4/3 )O 6 in a projection along [100] showing the layer stacking along [001].[(Fe,Te)O 6 ] units are shown in the polyhedral representation (red octahedra), Na atoms (blue) with bonds to the O atoms.Displacement ellipsoids are drawn at the 74% probability level.

Figure 3 (
Figure 3 (a) Reconstructed reciprocal h0l plane of Na 2 (Fe 2/3 Te 4/3 )O 6 ; (b) reflections belonging to the two twin domains are marked in green squares (domain 1) and orange circles (domain 2); reflections of the two domains overlap in every third row h.