科研之友
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摘要
In this study we present an alternative approach to separating.. contributions to the NMR shift originating from the Knight shift and chemical shielding by a combination of experimental solid-state NMR results and ab initio calculations. The chemical and Knight shifts are normally distinguished through detailed studies of the resonance frequency as a function of temperature and carrier concentration, followed by extrapolation of the shift to Zero carrier concentration. This approach is time-consuming and requires studies of multiple samples. Here, we analyzed Pb-207 and Te-125 NMR spin-lattice relaxation rates and NMR shifts for bulk and nanoscale PbTe. The shifts are compared with calculations of the Pb-207 and Te-128 chemical shift resonances to determine the chemical shift at zero charge carrier concentration. The results are in good agreement with literature values from carrier concentration dependent studies. The measurements are also compared to literature reports of the Pb-207 and Te-128 Knight shifts of n- and p-type PbTe semiconductors. The literature data have been converted to the currently accepted shift scale. We also provide possible evidence for the %26quot;self-cleaning effect%26quot; property of PbTe nanocrystals whereby defects are removed from the core of the particles while preserving the crystal structure.
- 出版日期2013-5-2
