Band structure pressure effects

For the alkali metal halides the influence of the anion is practically non-existent as can be seen from the comparison of RbCl, RbBr and Rbl (Table 3). In the more covalent structures both atoms appear to be effected by increase in pressure, as changes in the band structure lead to an increase in conductivity. 

Fig. 27. Temperature and pressure effect on the areas of the IR bands associated with P-sheets, disordered/tum structures and a-helices of SNase at pH 5.5 and 25 °C.

Hall effect measurements are reported for three single crystals of the charge transfer salt HMTSF-TCNQ in the temperature range 1.4-200 K at ambient pressure and under hydrostatic pressures of approximately 6 Kbars. There is evidence that the high conductivity of this material at low temperatures arises from a small number of electrons with a high mobility and a low degeneracy temperature as suggested by other experiments and a recent band-structure calculation. 

The effect of bending of the nitro group indicates how a band-gap closure can be achieved. The question remains, however, weather appreciable bending of the NO2 group inside the nitromethane crystal can be achieved within the experimentally accessible pressure range. This can be addressed through electronic structure calculations on the effect of static pressure, uniform and uniaxial, on the optical gap of nitromethane. The pressure effect is also studied with the presence of molecular vacancies to examine the combined pressure vacancy effect on the band-gap structure. 

Piezoresistive sensors. To measure the pressure, the resistance change to stress (the piezoresistance effect) may be employed. When silicon is stressed, the resulting strain breaks the cubic symmetry of the underlying crystal structure. The band structure of silicon is very sensitive to its crystal structure and, as a result, the consequent modification causes changes in the resistivity of the material (holes in the case of p " material). This change is... 

---