NMR STUDY OF SELF-DIFFUSION AND ELECTRONIC STRUCTURE OF METALLIC COPPER IN SOLID AND LIQUID STATES

The Knight shift K and the nuclear relaxation times T1 and T2 of Cu in metallic copper have been measured in the temperature range from room temperature up to the metal melting point, and into the liquid state up to 1200°C. A pulse technique was used. T1 and T2 were measured with an accuracy of ±3%, using a spin echo method. T2 becomes equal to T1 at high temperatures. From the data of T2 versus temperature, the diffusion constants for the Cu self-diffusion were calculated using the Eisenstadt-Redfield approach. The values of these constants are ED=1.97±0.04 eV and D0=0.11±0.05 cm2 sec-1 for Cu63, and ED=2.00±0.04 eV and D0=0.15±0.07 cm2 sec-1 for Cu65. The electronic structure of Cu was deduced from the effect of lattice expansion on K and T1. Assuming a free-electron model, one expects both (T1T)-1 and K to be temperature-independent. However, an increase of ∼10% in (T1T)-12 and K was observed as the temperature was raised from 25°C to the mp. Upon melting, there is a jump of 5.0±0.5% in (T1T)-12 and K. In the liquid phase, K rises moderately, whereas (T1T)-12 shows a steep rise of 5% per 100°C. This behavior is identical for both isotopes. It is shown that the main mechanism for the nuclear relaxation is the interaction with the conduction electrons. As the (T1T)-12 and the K temperature dependence cannot be explained by the free-electron model, we relate the behavior to the well-known band structure, using recent measurements and calculations which give the dependence of the density of states on the lattice constants. The jump in (T1T)-12 upon melting is explained in terms of the removal of the Fermi-surface distortion. No explanation is offered for the rise in (T1T)-12 with temperature in the liquid state. © 1969 The American Physical Society.