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'Nuclear quadrupole resonance' in keywords Facet   Publication Year 1994  [X]
Facet   section ZfN Section A  [X]
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1Author    M. Ariusz, M. Aćkow Iak, M. Arek BojarskiRequires cookie*
 Title    Automatically Tuned Probe Head System for Pulsed NQR Spectroscopy in Extreme Thermodynamic Conditions * M ich ał O stafin  
 Abstract    A com plete N Q R probe-head system operating in the frequency ranges 0 .5 -1 5 0 and 150— 300 M H z is described. The head is particularly suited for N Q R experiments carried out at a remote location, for example in a low-temperature cryostat or high-pressure chamber. M oreover, the head system includes a microprocessor-controller for automated tuning of the probe to the operating frequency of the associated N Q R spectrometer. The controller can be easily interfaced to a PC via standard serial port. 
  Reference    Z. Naturforsch. 49a, 42 (1994); received July 23 1993 
  Published    1994 
  Keywords    Nuclear quadrupole resonance, Pulsed spectrometers, Instrum entation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0042.pdf 
 Identifier    ZNA-1994-49a-0042 
 Volume    49 
2Author    G. L. Petersen, P. J. Bray, R.A M ArinoRequires cookie*
 Title    A New Pulsed Nuclear Quadrupole Resonance Spectrometer  
 Abstract    A new pulsed nuclear quadrupole resonance spectrometer is described and a number of Nitrogen-14 spectra are shown and discussed. The spectrometer is computer interfaced and both data acqui­ sition and all adjustments other than the matching network tuning are automatic. Spectra may be produced using fast Fourier transforms or by the Clark Method. The latter is particularly valuable when very wide line widths are encountered. 
  Reference    Z. Naturforsch. 49a, 65—7 (1994); received November 18 1993 
  Published    1994 
  Keywords    Nuclear quadrupole resonance, Spectrometer, Instrumentation, Fourier transform 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0065.pdf 
 Identifier    ZNA-1994-49a-0065 
 Volume    49 
3Author    J. Pelzl, C. DimitropoulosRequires cookie*
 Abstract    Recent and novel data obtained from chlorine NQR measurements on natural and deuterated (NH4)2 MC16 compounds are discussed with special regard to the influence of the ammonium-ion dynamics on the structural stability of these crystals. The temperature dependence (4.2 K to 350 K) of the chlorine NOR frequency \ q and relaxation rates Tj-1 , T2-1 obtained from the natural ammonium salts of Sn, Pd, Os, Pb, Te, Se and from the deuterated salts of Sn, Te and Se are analysed. Slight deviations from the normal temperature behaviour of vQ and Tt~ 1 are found in Sn, Pd and Os compounds which stay cubic in the whole temperature range. The ammonium compounds of Pb and Te undergo a structural transformation between 80 K and 90 K from the cubic to a trigonal phase which is distinguished by the preservation of the single line spectrum of the chlorine NQR below rel. The observed divergence of Tl_ 1 at the transition point can be described in terms of a spin-phonon process in the presence of an overdamped soft mode. Deuteration of (N H 4)2 TeCl6 only slightly affects the transition of Tcl but leads to new structural changes at lower temperatures. Whereas the natural compound stays trigonal down to 4.2 K the deuterated crystal undergoes two additional structural transformations at Te 2 = 48 K and Tc3 = 28 K which are correlated with a slowing down of the deuteron motion. Approaching Tc2 from above, the spin-lattice relaxation rate and the spin-spin relaxation rate of the chlorine NQR exhibit distinct anomalies which are attributed to limited jumps of the octahedron in a shallow potential. The barrier height of this potential deduced from the chlorine NQR spin-lattice relaxation rate is 400 K. The transition at Tc2 is explained by the condensation in one minimum of this potential. At Tc3 a long range correlation is formed which is accompanied by a rotation of the octahedron about its fourfold axis. A similar mechanism is adopted for the transitions observed in (NH4)2 SeCl6 at Tc= 24 K and in (ND4)2 SeCl6 at Tc = 48 K. 
  Reference    Z. Naturforsch. 49a, 232—246 (1994); received August 12 1993 
  Published    1994 
  Keywords    Nuclear quadrupole resonance, Structural phase transitions, Ammonium-ion dynam­ ics, Hexahalogenometallates, Critical behaviour 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0232.pdf 
 Identifier    ZNA-1994-49a-0232 
 Volume    49