DIFFRACTOMETRY UNDER HIGH PRESSURES

Milos Steinhart

Institute of Macromolecular Chemistry, Prague, Czech Republic

Perm. Address: University of Pardubice, Studenská 84, Czech Republic

Pressure and temperature are the main thermodynamic parameters and considerably influence the behavior of matter. Studies of changes caused by varying these parameters are both important and interesting and deepen our knowledge about the world around us. Temperature measurements are well established and instrumentation improvements are necessary perhaps mainly if very high accuracy or special control is needed. On the other hand, pressure measurements are relatively much younger. The, macroscopic effects on material caused by pressure have been all around us and many were used for centuries. They even had historical consequences e.g. when hammering iron weapons and this was almost without any knowledge on the microscopic level. But the beginning of serious experiments goes back less than a hundred years and the field is still under a fast development in several directions. The behavior dependence on pressure is being studied by many techniques. Among them, particularly, diffraction and scattering methods, which can “see” into the structure, are very important.

One of the recent instrumentation frontiers is, naturally, the highest-pressure edge. Into this group mainly improvements of diamond anvil cell techniques belong. Other direction is high pressure combined with other extreme sample environment properties, mainly high temperature. Here several kinds of multi-anvil presses are employed. Quite special are methods dedicated to polymer and biopolymer studies where some other properties are preferred to maximum pressure. These are mainly a relatively big volume but also, for instance, a possibility to change operatively the sample environment, such as the chemical content of the solution.

This contribution is trying to lay a physical basis and show the main techniques and their principles recently used for reaching high pressures. Then it illustrates the recent development in the main directions. We are trying to prove that reaching very high pressures is not just a simple competition among labs but rather a competition with the nature due to the astrophysical, geophysical but also biological consequences.

[1] A. Jayaraman, Rev. Sci. Instrum. 57 (6) (1986) 1013 – 1031

[2] M. Steinhart, in Exp. metody v rtg. a neutronové analýzy (1994), 209-216

[3] High-pressure Techniques in Chemistry and Physics, W. B. Holzapfel & N. S. Issacs, Eds., Oxford Uni. Press 1997

The research was supported by the Grant Agency of the Czech Republic (Project No.: 203/00/13170) and the Academy of Sciences of the Czech Republic (Project No.: AVOZ 4050913)