Fluorine and proton spin absorption and relaxation in solid ammonium heptafluozirconate

Abstract

H 1 magnetic resonance absorption in (NH4)aZrF7 has been studied over the temperature range 20 ~ to -196~A line width transition due to low activation energy reorientations of two types of NH4 + ion was observed. The fluorine absorption data give also evidence of reorientation of zirconiumfluorine complex. The transient experiment carried out at 15-3 and 22.9 Mc/sec in the same temperature interval supports the absorption results by indicating conclusively that two motions are effective in the crystal studied. The slower one is the zirconium-fluorine ion reorientation, the faster one, the reorientation of the weakly hydrogen-bonded NH4 + ions. The relaxation data exhibit strong F-H and H-F cross relaxations: at higher temperatures fluorines and protons relax essentially through the slower motion of the zirconium-fluorine complex, while at lower temperatures both spins relax through the high frequency reorientation of the NHC ions. The observed dynamic disorder is compatible with the Hampson-Pauling interpretation of the (NHa)aZrF7 structure and thus supports implicitly the existence of the (ZrFT)---complex.

Time-dependent electric quadrupole interactions in (NH4)3HfF7

“…Therefore it is reasonable to expect reorientation processes at elevated temperatures. This assumption is strongly supported by the results of Pintar et al [9], who investigated the isomorphous Zrcompounds by NMR.…”

“…These results are also in striking agreement with NMR measurements at 19F in the isomorphous Zr-compound. Pintar et al [9] related the temperature dependence of the line shape to a relaxation behaviour, which should be caused by an activation process with an activation energy of 8 (2) kcal/ mole corresponding to 0.35 (8) eV.…”

A neutron diffraction analysis of the disorder in ammonium heptafluorozirconate

“…Nuclear magnetic resonance studies have shown that the ZrF~-ions and NH + ions in (NHa)3ZrF7 are dynamically disordered and reorienting (Blinc & Lahajnar, 1967;Pintar, Lahajnar & Slivnik, 1966). The present neutron study was begun to determine the nature of the disorder of the ammonium ions.…”