<p> The temperature dependences of the deuteron spin-lattice
relaxation times, T1, in ferroelectric ammonium sulfate, (ND4)2SO4 , and
ammonium fluoroberyllate, (ND4)2BeF4, have been studied by transient
methods over the range 80 to 47S°K. The ability to resolve the
individual correlations of the two independent ND4 groups in the deuteron
experiment has thrown new light on the reorientation of the ammonium
groups and their behaviour in the phase transition.
It has been proposed that the mechanism of the phase transition
in ammonium sulfate is a disordering, with respect to the a b plane in
the paraelectric phase, of the ND4 dipoles which also make the dominant
contribution to the spontaneous polarization. The present N.M.R. results
show that in (ND4)2so4 ,T1 at both non-equivalent ND4 groups is affected
at the phase transition, whereas in (ND4)2BeF4 , it is affected at only
one ND4 group. This suggests that the phase transitions in these two materials are rather different and that in ammonium sulfate both types of ammonium ions are involved whereas in ammonium fluoroberyllate only one type is involved in the transition. Such a conclusion is supported by evidence from measurements of thermal and dielectric properties.
An earlier study of the proton spectrum in (NH4)2so4 reported a
value of 33 gauss^2 for the second moment at 20°K. This is considerably
smaller than the expected rigid lattice value of 5O gauss^2 and it was
concluded that while some of the NH4+ groups are effectively rigid at
20°K others are still reorienting. Our new results for the proton second moment confirm the low value down to 4.2°K but our results for T1 indicate that the proton line is not motionally narrowed. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18569 |
| Date | 11 1900 |
| Creators | Kydon, Donald |
| Contributors | Petch, H. E., Physics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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