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'Thermal Decomposition' in keywords Facet   Publication Year 1988  [X]
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1Author    Schaffrath, R. GruehnRequires cookie*
 Abstract    Single crystals of the new oxochlorotantalate Nd 7 , 1 Ta 8 0 2H Cl f , could be obtained only by chemical transport reactions (T 2 —» T,; T 2 — 1000 °C, T, = 900 °C) with mixtures of Cl 2 /TaCl 5 as transport agent. NdTa0 4 was chosen as the starting material. A direct preparative route to Nd 7 ,,Ta s 0 2x Cl(, from binary and ternary components, however, was not successful. Nd 7 33 Ta H Oi x Clf, crystallizes in the space group Cmmm with a = 10.3381(8) Ä, b = 18.865(1) A, c — 3.9152(3) A; Z = 1. The structure was refined to R — 4.42%, R w = 2.76%. Main building units are pairs of edge-sharing Ta0 6 -octahedra which are connected with threefold capped trigonal prisms around Nd. Especially remarkable is one Nd position with an occupation factor of 0.833. The relationship of this new structure type with Nd 2 Ta 2 0 7 Cl 2 is considered. Furthermore, we have measured the magnetic susceptibilities of both Nd-compounds in a temperature range from 3,6 to 251,3 K. The results are compared with calculated data. 
  Reference    Z. Naturforsch. 43b, 1567—1574 (1988); eingegangen am 7. Juli 1988 
  Published    1988 
  Keywords    Oxochlorotantalates, Thermal Decomposition, Preparation, Chemical Transport Crystal Structure 
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 TEI-XML for    default:Reihe_B/43/ZNB-1988-43b-1567.pdf 
 Identifier    ZNB-1988-43b-1567 
 Volume    43 
2Author    Klaus-Jürgen Range, Reinhard Zintl, AntonM. HeynsRequires cookie*
 Title    The Thermal Decomposition of Ammonium Metavanadate(V) in Open and Closed Systems  
 Abstract    The thermal decomposition of ammonium metavanadate(V) has been studied at atmospheric pressure, at hydrothermal, and high-pressure conditions, respectively. In a closed high-pressure system a redox reaction between vanadium(V) and ammonia takes place, to yield with increasing temperature the compounds (NH 4) 2 V 6 0 12 (0H) 2 , VO : _ A (OH) A , and V 2 "0 2 "_,, the composition of the product eventually approaching V 2 0 3 at 1100 °C. All these compounds can easily be con-verted into V 2 O s by heating in air. The mid-infrared spectra of the decomposition products obtained by slow heating of NH 4 VO, in air, are virtually identical and show that ammonium hexavanadate(V), (NH 4) 2 V h O| 6 , is the most important, and perhaps only, intermediate in the "non-reduction" case. On further heating, (NH 4) 2 V 6 0 lft may not only loose ammonia and water to form V 2 0 5 but could as well partially be reduced by ammonia. This could explain the diversity of intermediate "compounds" described in the literature. Hydrothermal reaction of NH 4 VO, yielded (NH 4) 05 V 2 O 5 , (NH 4) 2 V,0 8 , and V 2 0 3 at rather low temperatures. 
  Reference    Z. Naturforsch. 43b, 309—317 (1988); received November 9 1987 
  Published    1988 
  Keywords    Ammonium Metavanadate(V), Thermal Decomposition, High-pressure Reactions, Hydrothermal Reactions 
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 TEI-XML for    default:Reihe_B/43/ZNB-1988-43b-0309.pdf 
 Identifier    ZNB-1988-43b-0309 
 Volume    43