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Nmr Study of Cluster-Assembled Nanophase Copper
Published online by Cambridge University Press: 25 February 2011
Abstract
63Cu and 65Cu NMR spectra from cluster-assembled nanophase copper with an average grain size between 5 and 10nm show a broadened peak, at the normal Knight-shifted frequency for copper metal, which arises from only the central 1/2 to -1/2 transition. A very broad background is observed on either side of that peak. Some samples exhibit a second broad peak at a position normally associated with non-metallic copper. Pulsed NMR measurements of the central peak show that virtually all the copper signals are significantly broadened and have a spin-spin relaxation time longer than larger grained copper samples. Line shape measurements, using spin echoes, as a function of delay between rf excitation and measurement show there are a number of copper sites with longer relaxation times which have a significantly larger broadening. Those sites are tentatively identified as being at or near a grain boundary or free surface. A small orientation effect is observed indicating an anisotropy within the samples. An isochronal anneal of one sample showed significant, but not complete, line narrowing after an anneal at 450°C consistent with other nanophase metals which show grain growth above 40-50% of the melting temperature.
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- Copyright © Materials Research Society 1993