Electron variation with lattice parameter

Intramolecular vibrations strongly scatter electrons near the Femii-surfacc in doped fuUerenes. A simple expression for the electron-phonon coupling parameters for this case is derived and evaluated by quantum-chemical calculations. The observed superconducting transition temperatures and their variation with lattice constants can be understood on this basis. To test the ideas and calculations presented here, we predict that high frequency Hg modes acquire a width of about 20% of their frequency in superconductive foUerenes, and soften by about 5% compared to the insulating fuUerenes. 

As can be seen in Figure 6, Tc of RM2B2C compounds also much depends on the lattice parameters. As an example the dashed line represents the variation of Tc in a series with non-magnetic elements R. It should be noted that the effects of lattice parameters in Figure 6 cannot be explained by only taking into account the variation of N( p) in the expression (3), caused by the variation of the lattice parameters. In particular in CeN E C and YbN E C superconductivity is suppressed by strong hybridization of 4f electrons with conduction electrons (see Sections 4.2 and 4.12). 

In crystals with a high concentration of shallow donors or acceptors, another contribution to the volume change at room temperature is the presence of free carriers in the continuum. This effect is related to the minimization of the total energy of the crystal compared to that of the undoped crystal ([24] and references therein). This purely electronic effect has been considered, together with the eventual presence of a high concentration of native defects, in the variation of the lattice parameter of Si-doped GaAs conducting substrates used in the electronic industry [3],... 

This proves that only the extended tr-electron system of the diacetylene backbone is responsible for the enhanced polarizability. This conclusion is supported by the experimental analysis for three orthogonal directions in TS single crystals shown in Fig. 9.33 [75]. The minor variations for the two orthogonal directions (2) and (3) can be explained by the changes of the lattice parameters. In contrast, the change of the respective lattice parameters with polymer content does not suffice to explain the change of Ae. ... 

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