Diamond Anvil Cells are among the most powerful tools employed in High-Pressure research. They allow to attain static pressures up to several hundreds of kilobar by compression of small volume samples
The DAC has enabled us to obtain phase stability information. Scientists constantly endeavor to improve DAC experimental techniques in order to obtain better data and to obtain further information about the physical properties of any material. With the addition of a laser or a resistance heater or with cryogenic cooling, we can also use the DAC to explore the pressure, volume, temperature relationship and the resulting structural changes of any material its equation of state and phase diagram. Higher pressure and increased temperature may force further structural changes, until the material loses its crystal structure entirely that is, it melts.
These include techniques for low- and high-temperature studies, x-ray diffractometry, spectroscopy with the DAC, and other measurements. Results on selected materials, with a view to illustrating the physics behind high-pressure phenomena, are presented and discussed from years. These include metal-semiconductor transitions, electronic transitions, phonons and high-pressure lattice dynamics, and phase transitions. A whole section is devoted to the behavior of condensed gases, principally H2, D2, O2, N2, and rare-gas solids.
The concept underlying the Diamond Anvil Cell system is very simple. The sample, held between two diamond anvils and confined by a gasket, is squeezed between the anvils’ small faces. The maximum pressure value varies according to the dimensions of the small faces of the diamond anvil (culets), to the force exerted on the diamonds as well as to the dimensions of the hole in the gasket.
DAC technology thus provides an inexpensive way to compress tiny samples of materials to ultra-high pressures in order to identify changes in their properties. Pressure is measured by observing the fluorescence properties of the investigated target (eg. Ruby crystal) with a green laser.
The idea that high pressure may be attained through the application of a modest force on a microscopic area has to be ascribed to Drickamer. He, in the early 50es performed high-precision measurements of electric resistivity, X-ray diffraction and optical absorption at pressures of up to tens of a Gpa.
In the following years, different and new types of diamond anvil cells were built, thus allowing the start of a new era, that of high pressures. In 1965 the metal gasket technique was employed in order to generate hydrostatic pressure 3. thus allowing the pressurization of liquids and gases. The ruby-fluorescence technique for pressure calibration was introduced in 1973.
