| 1. |
- Kosa, Ladislav, et al.
(författare)
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Phase transitions of K2TaF7 within 680-800 degrees C
- 2008
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Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 6:1, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- Three thermal effects on heating/cooling of K2TaF7 in the temperature interval of 680-800 degrees C were investigated by the DSC method. The values determined for the enthalpy change of the individual processes are: Delta H-transII(m)(K2TaF7; 703 degrees C) = 1.7(2) kJ mol(-1), Delta H-transI(m)(K2TaF7; 746 degrees C) = 19(1) kJ mol(-1) and Delta H-transIII(m)(K2TaF7; 771 degrees C) = 13(1) kJ mol(-1). The first thermal effect was attributed to a solid-solid phase transition; the second to the incongruent melting of K2TaF7 and the third to mixing of two liquids. These findings are supported by in situ neutron powder diffraction experiments performed in the temperature interval of 654-794 degrees C.
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| 2. |
- Langer, Vratislav, 1949, et al.
(författare)
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Dipotassium heptafluorotantalate(V), β-K2TaF7, at 509 K
- 2006
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Ingår i: Acta Crystallographica Section E: Structure Reports Online. - 1600-5368. ; E62:4, s. i91-i93
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Tidskriftsartikel (refereegranskat)abstract
- Upon heating to 509 K, monoclinic α-K2TaF7 (P21/c) transforms to orthorhombic β-K2TaF7 (Pnma) which is composed of discrete K+ cations and TaF72- anions. In the anion, the Ta atom is sevenfold coordinated by F atoms, with the Ta-F distance varying from 1.88(2) to 1.965(19) Å. The two independent K+ cations are surrounded by F atoms positioned within 2.740(17)-2.979(10) and 2.989(17)-3.15(5) Å. Ta, both K and one of the four F atoms are located on a mirror plane, Wyckoff position 4c.
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| 3. |
- Langer, Vratislav, 1949, et al.
(författare)
-
Redetermination of Na3TaF8
- 2010
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Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C66:9, s. i85-i86
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of trisodium octafluoridotantalate,Na3TaF8, has been redetermined using diffractometer data collected at 153 K, resulting in more accurate bond distances and angles than obtained from a previous structure determination based on film data. The structure is built from layers running along [101], which are formed by distorted [TaF8] antiprisms and [NaF6] rectangular bipyramids sharing edgesand corners. The individual layers are separated by eightcoordinated Na ions. Two atoms in the asymmetric unit are in special positions: the Ta atom is on a twofold axis in Wyckoff position 4e and one of the Na ions lies on an inversion centre in Wyckoff site 4d.
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