High Pressure as an Experimental Variable

High pressure has traditionally been viewed as a macroscopic, thermodynamic experimental variable. Classic applications of pressure have involved equation of state studies of liquids and soHds and measurements of the variation of physical properties as a function of pressure [57,59 - 66]. The basic effect of pressure on a system is a consequence of the thermodynamic stabiHty requirements of the second law [67] and can be expressed most generally as 

Equation (1) indicates that, in order to comply with the second law, the volume of a material must decrease upon isothermal compression. The precise maimer, however, in which a material reduces its volume in response to an applied pressure is unspecified by the second law and requires consideration on a molecular level. Molecular attributes such as bond angles, bond lengths, covalency, coordination number, and intermolecular forces can be influenced by pressure. Since these attributes are responsible for defining chemical, electrical, optical, and magnetic properties, pressure is a potentially powerful probe of the properties of materials. 

When considering the potential effect of pressure on a system, it is useful to recognize the magnitude of pressure required to significantly alter molecular and bulk properties. The isothermal compressibility, k (or its reciprocal K, the bulk modulus) (Eq. 2), gives an indication of the sensitivity of a system to pres- 

Our focus in this review is on the luminescence behavior of solid state lanthanide and transition metal systems over a pressure range extending up to 300 kbar. Since this magnitude of pressure is well beyond everyday experience, it is beneficial to consider how these pressures compare to those encountered in the physical world. Table 1 presents selected examples from a more comprehensive compilation presented by Jayaraman [68]. The pressures in Table 1 range from 10 bar in outer space to 10 bar at the center of the sun. The unit of pressure of relevance to this review is the kbar. From Table 1, we see that 1 kbar corresponds approximately to the pressure at the deepest point in the ocean. A pressure of 50 kbar would result if one were to invert the Eiffel tower and place it on 

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NMR relaxation or line width measurements are sensitive to the degree of crystallinity in solid polymers, because the protons in the crystalline lattice experience strong dipole-dipole interactions which cause fast spin-spin relaxation and line broadening. As a result, line width and relaxation studies have been used to measure crystallinity in a broad range of polymers. The use of high pressure as an experimental variable in NMR studies of polymer crystallinity offers new details about polymer crystallization. The study of pressure and temperature effects on the... 

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