Trapping by Dislocations in α’-PdDx Observed by NMR
Spin-spin relaxation of 2D in α’-PdD0.64 measured by a CPMG sequence exhibits two coexisting relaxation times, T2b < T2a both much less than the spin-lattice relaxation time T1 at 20°C, when the sample is loaded from the gas phase so that it passes through the α-α∃ two-phase region. T1 is explained by a fluctuating quadrupolar interaction with electric field gradients due to the motion of neighbouring deuterons. T2a must be predominantly due to some other mechanism, identified as interaction with field gradients due to long-range strain fields of dislocations, with a much longer correlation time than that characterizing the T1 mechanism. T2b is tentatively ascribed to deuterons trapped in dislocation cores, since this decay is absent in a sample loaded under high pressure so as to avoid the mixed-phase region and thus greatly reduce the dislocation density. The signal amplitude associated with T2b is temperature dependent with an activation energy ~ 40 meV which would represent the deuterium-dislocation interaction energy. A difficulty with this interpretation is the large apparent fraction of trapped deuterium.
KeywordsDislocation Density Electric Field Gradient Quadrupolar Interaction Dislocation Core Scripta Meet
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