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1998[X]
1Author    Tetsuo Asaji, Keizo Horiuchi, Takehiko Chiba, Takashige Shimizu, Ryuichi IkedaRequires cookie*
 Title    NMR * NQR and DTA * DSC Studies of Phase Transitions in Pyridinium Tetrachloropalladate(II) and Pyridinium Tetrachloroplatinate(II)  
 Abstract    From the measurements of DTA • DSC and the temperature dependences of 35 C1 NQR frequen-cies, phase transitions were detected at 150 K, 168 K, and 172 K for (pyH) 2 [PtCl 4 ], and at 241 K for (P yH) 2 [PdCl 4 ], In order to elucidate the motional state of the constituent ions in the crystals in connec-tion with the structural phase transitions, the 35 C1 NQR and 'H NMR spin-lattice relaxation times and the second moment of the 'H NMR line were measured as functions of temperature. For both com-pounds, the potential wells for the cationic reorientation are suggested to be highly nonequivalent at low temperatures. Above 168 K, the pyridinium ions in (pyH) 2 [PtCl 4 ] are expected to reorient between almost equivalent potential wells. As for (pyH) 2 [PdCl 4 j, it is expected that the orientational order of the cation still remains even above the second order transition at 241 K. A change of the potential curve from two-unequal to three-unequal wells is proposed as a possible mechanism of the second order tran-sition. The activation energies for the cationic motion in the respective model potential are derived for both compounds at high and low temperatures. 
  Reference    Z. Naturforsch. 53a, 419—426 (1998); received December 30 1997 
  Published    1998 
  Keywords    Phase transition, NQR, NMR, Spin-lattice relaxation, DSC 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0419.pdf 
 Identifier    ZNA-1998-53a-0419 
 Volume    53 
2Author    V. Berbenni, A. Marini, D. CapsoniRequires cookie*
 Title    Solid State Reaction Study of the System Li 2 C03/Fe 2 03  
 Abstract    A thermoanalytical (TGA/DSC) and diffractometric (XRD) study has been performed on the solid state reaction system Li 2 C0 3 -Fe 2 0 3 in the x Li range 0.10-^0.50. A detailed analysis of the results shows that the data are in agreement with a reaction model where the carbonate decomposition is regulated by the formation of both LiFe0 2 and LiFe 5 0 8 , and the relative amount of the two phases depends on the initial composition. The DSC evidence offers the possibility to directly quantify the LiFe 5 O x phase. Fur-thermore it allows one to obtain the enthalpies of formation of both LiFe0 2 and LiFe 5 0 8 . 
  Reference    Z. Naturforsch. 53a, 997—1003 (1998) 
  Published    1998 
  Keywords    Lithium Ferrites, Solid State Reaction, Iron (III) Oxide, Lithium Carbonate, TGA, DSC 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0997.pdf 
 Identifier    ZNA-1998-53a-0997 
 Volume    53