Conduction electron, compression

Most of these studies, mainly in the period 1955 to 1970, have been concerned with cathodic hydrogen evolution. Different parameters characterizing the bulk properties of each metal have been adduced, including physical parameters such as electron work funchon, electrical conductivity, hardness, compressibility, temperature of evaporation, and heat of evaporation, and chemical parameters such as the affinity to hydrogen or oxygen. 

Finally let us return to the volume dependence of isomer shift. In fig. 28 (bottom) a strong deviation from the linear extrapolation of initial slope dS/dln V = 15mm/s is apparent. The change in contact density by the compression of conduction electrons can be described by (Kalvius et al. 1974)... 

The volume dependence of p(0) is expected to be hyperbolic and indeed such a fit connects very well the experimental points (solid line in fig. 28, bottom). Volume reduction simply compresses the conduction electron gas. This result questions somewhat the suggested break around 15GPa in the S(F) dependence of EuO (see Abd-Elmeguid and Taylor 1990) which had been derived from linear fits. In one sense this point is academic since a valence change was excluded from the lack of temperature variation. But one may ask why the occurrence of an insulator-metal transition is not reflected in the isomer shift. 

High-pressure experiments up to 8.3 GPa at 4.2 K were carried out by Kratzer et al. (1986). The observed rise in Curie temperature dTc/dP = 3.5 0.3 K GPa is well within the range predicted by a calculation using a modified RKKY exchange (Jaakkola and Hanninen 1980). The pressure coefficient of is extremely small dB, [/dP= — 0.4 0.1 TGPa Similarly, the ionic electric field gradient decreases by 5% between ambient pressure and 8.3 GPa. Isomer shifts exhibit the linear pressure dependence expected from a compression of mainly s-like conduction electrons. 

In contrast to the above compounds, RCu2 (R=Gd, Tb) the magnetic transition temperature decreases under pressure (Luong and Franse 1981). The authors explained this behavior by the decrease of the density of states at the Fermi level caused by the expansion of the conduction electron band under compression. The exchange integral variation was not taken into account. 

To illustrate the effect of radial release interactions on the structure/ property relationships in shock-loaded materials, experiments were conducted on copper shock loaded using several shock-recovery designs that yielded differences in es but all having been subjected to a 10 GPa, 1 fis pulse duration, shock process [13]. Compression specimens were sectioned from these soft recovery samples to measure the reload yield behavior, and examined in the transmission electron microscope (TEM) to study the substructure evolution. The substructure and yield strength of the bulk shock-loaded copper samples were found to depend on the amount of e, in the shock-recovered sample at a constant peak pressure and pulse duration. In Fig. 6.8 the quasi-static reload yield strength of the 10 GPa shock-loaded copper is observed to increase with increasing residual sample strain. 

---