Freudenbergite

Abstract

Na2Fe2Ti6Ol6 , monoclinic, C2/m, a = 12.267(6), b = 3.823 (5), c = 6.483 (3) A, fl = 107.16 (5) °, Z = 4, D x = 3.97 g cm -3. The crystalswere prepared by heating a mixture of Fe and TiO 2 in 10 M NaOH solution, sealed in a gold tube, at 650°C and 1000 atm for 21 days. Black platy crystals were obtained.The substance is isostructural with Na0.2TiO2, with mean M(1)-O, M(2)--O and Na-O distances of 1.993, 1.973 and 2.715 A respectively.

Low-temperature synthesis of freudenbergite-type titanate bronzes from metal halides, crystal growth from molybdate flux, and crystal structure determination of Na1.84Zn0.92Ti7.08O16

“…The structure refinements using synchrotron powder data are based on the structure model from Ishiguro et al [7] and essentially confirm the literature knowledge (Figs. 1 and 2, Table 1).…”

“…Lattice parameters and atomic positions of the Fe-containing single crystals described in Ref. [7] were reproduced very well for the powders investigated in this study.…”

“…According to the literature model of the Fe-containing freudenbergite-type phase [7] there are two metal atom sites (Wyckoff symbol 4i) occupied by iron and titanium. The original structure refinement based on single-crystal data and resulted in the formula Na 2 (Ti 2.92 Fe 1.08 )(Ti 3.08 Fe 0.92 )O 16 [7].…”

“…Later, its composition and crystallographic description was questioned, reinvestigated and corrected, suggesting that freudenbergite crystallizes monoclinically with the approximate formula Na 2 M y Ti 8Ày O 16 [2][3][4]. In the following, similarities with synthetic bronzes were recognized and repeatedly discussed [5,6], until Ishiguro et al succeeded in growing hydrothermally single crystals of synthetic freudenbergite, Na 2 (Fe 1.08 Ti 2.92 )(Fe 0.92 Ti 3.08 )O 16 , establishing its crystal structure in the monoclinic crystal system, space group C2/m [7]. The crystals were black and plate-like.…”

“…Structure refinements were performed based on structure model from literature [7] using the Rietveld method, program TOPAS 4.2 [15]. Positional parameters and occupancies were refined freely.…”