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2000 (1)
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1996 (1)
1Author    J. M. Ramallo-López, F. G. Requejo, A. G. Bibiloni, M. Rentería, L. Gutierrez, E. E. MiróRequires cookie*
 Title    Combined TDPAC and EXAFS Study of InPt/FER Catalysts  
 Abstract    Time Differential Perturbed Angular Correlation (TDPAC) experiments using 111 In as probe were performed in order to determine the nature of In-sites in In-ferrierite (In/FER), before and after the incorporation of Pt through the hyperfine interaction between the nuclear quadrupole moment of the probe's nucleus and the extranuclear electric field gradient (EFG). Extended X-ray Absorption Fine Structure (EXAFS) measurements were performed to measure the absorbance above the Pt's L m absorption edge in the transmission mode in order to determine the local environment of Pt atoms in Pt/FER and InPt/FER catalysts. TDPAC spectra of 111 In in In/FER and InPt/FER taken at 500°C in air indicated that there are no changes in the indium surroundings after the incorporation of Pt. Three sites were found for indium in both samples. Two of them correspond to the two sites of indium in ln 2 0 3 and the third one is attributed to In in exchange sites of the zeolites. Their population, quadrupole frequencies and asymmetry parameters didn't change with the incorporation of Pt. EXAFS experiments showed similar near neighborhood Pt-0 distances and Pt coordination number in Pt/FER and InPt/FER samples. There is no evidence of the presence of any In-Pt bimetallic entity in InPt/FER catalyst. 
  Reference    Z. Naturforsch. 55a, 327—330 (2000); received August 26 1999 
  Published    2000 
  Keywords    Hyperfine Interactions, TDPAC, EXAFS, Catalysis, Ferrierite 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0327.pdf 
 Identifier    ZNA-2000-55a-0327 
 Volume    55 
2Author    P. Wodniecki, B. Wodniecka, M. Marszalek, A. Z. HrynkiewiczRequires cookie*
 Title    PAC Studies of Ag-Hf Intermetallic Compounds  
 Abstract    The hyperfine quadrupole interaction of 181 Ta and 111 Cd probes in HfAg and HfiAg com-pounds was studied at 24 to 1100 K with the time -differential perturbed angular correlation (TDPAC) technique. The EFGs measured in HfAg on 181 Ta and m Cd are 1.388(5)x 10 18 VcnT 2 and 0.340(5)x 10 lx Vcm -2 , respectively. For both probe atoms a linear decrease of the EFG with temperature was observed with slopes 1.1 l(2)x 10 -4 KT 1 and 1.73(5)x 10~ 4 KT 1 for 181 Ta and "'Cd, respectively. In Hf 2 Ag, 0.469(2)x 10 18 VcnT 2 was determined on 181 Ta nuclei and 0.428(5)x 10 18 Vcm -2 on '"Cd. Also a linear EFG temperature dependence with the large slope of 2.39(6)x 10 -4 K" 1 was observed for "'Cd probes in Hf 2 Ag, while the EFG measured on l8l Ta nuclei in this compound exhibits a very weak temperature variation which can be fitted neither with a linear T nor a T ?/2 dependence. In all cases the electronic contributions to the EFG are very small indicating that these transition element systems do not obey the universal correlation between the electronic and the ionic EFG observed in numerous other systems not belonging to the transition metal series. 
  Reference    Z. Naturforsch. 51a, 437—441 (1996); received November 20 1995 
  Published    1996 
  Keywords    Hyperfine interactions, perturbed angular correlations, electric field gradient, inter-metallic compounds, Ag-Hf system 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0437.pdf 
 Identifier    ZNA-1996-51a-0437 
 Volume    51 
3Author    P. Wodniecki, B. Wodniecka, A. Kulińska, A. Z. HrynkiewiczRequires cookie*
 Title    Electric Quadrupole Interaction at 181 Ta in Isostructural Orthorhombic Cu 8 Hf 3 and Cu 8 Zr 3 Compounds  
 Abstract    The quadrupole interaction of 181 Ta probes in isostructural Cu 8 Hf 3 and Cu 8 Zr 3 intermetallic compounds was studied in the temperature range 24 K -1100 K with the time-differential perturbed angular correlation technique. Two nonaxial electric field gradients corresponding to two nonequiv-alent hafnium or zirconium sites in the investigated structure were found. A linear decrease in the quadrupole interaction frequency with increase of temperature for the 8(d) sites was evidenced, while the v Q (T) dependence for the 4(c) sites is weaker and has a T 312 character. 
  Reference    Z. Naturforsch. 53a, 355—357 (1998); received October 31 1997 
  Published    1998 
  Keywords    Hyperfine Interactions, Perturbed Angular Correlations, EFG, Intermetallic Compounds, Cu-Hf and Cu-Zr Systems 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0355.pdf 
 Identifier    ZNA-1998-53a-0355 
 Volume    53