Elastic and piezoelectric properties of minerals I. Principles and experimental approaches
Jürgen Schreuer, Siegfried Haussühl, 2005. "Elastic and piezoelectric properties of minerals I. Principles and experimental approaches", Mineral behaviour at extreme conditions, Ronald Miletich
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Since the formulation of the “Law of Spring”, Ut Pondus sic Tensio by Robert Hooke in 1678, elastic properties of solids have been subject of intensive research in various fields of basic and applied sciences. For example, as the interior of our planet is not directly accessible by experiment, models of the structure of the Earth are mainly based on seismic data. The interpretation of seismic wave propagation and the derivation of equations of state in geosciences require a profound knowledge of the elastic and visco-elastic properties of the constituting mineral phases. All geological materials undergo phase transitions at certain thermodynamical conditions, which can lead to dramatic variations in their elastic properties. Often the influence of the transition extends over a wide temperature and pressure range. Therefore, elasticity serves as a highly sensitive probe for the investigation of structural instabilities related to phase transitions (Carpenter & Salje, 1998). Although most people are not aware, we cannot imagine life today without piezoelectric single crystals and ceramics. Most electronic devices make use of specific interactions between elastic and piezoelectric properties of crystal species like α-quartz and tourmaline. The so-called electromechanical coupling effects allow for conversion of mechanical into electrical energy and vice versa. Examples for technical applications are frequency filters and delay lines in communication technologies, ultrasound generators and clock oscillators. The pure piezoelectric effect is used in pressure sensors in combustion engines and gas turbines.
In view of the importance of elasticity and piezoelectricity it is rather surprising that relatively little is known about these basic physical properties of crystals.
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Mineral behaviour at extreme conditions
Extreme conditions and their effects on matter and materials are currently fashionable topics in modern science. Perhaps the fascination derives from the unimaginable dimensions that grab our attention and push the boundaries of our imagination. Imagine the pressures in extremely dense neutron stars where electrons and protons are fused together and atoms collapse to the density of an atomic nucleus; imagine temperatures of thousands of degrees Kelvin at the solar surface, or multimegabar and terapascal pressures deep within the interior of our planets. But even a simple droplet of water represents an extreme environment when it comes into contact with an otherwise stable crystal of rock salt, causing the crystal to dissolve as external conditions are drastically changed. We have an inherent desire to understand these diverse kinds of phenomena in nature, the mechanisms of the material changes involved, as well as the extreme conditions which are becoming increasingly demanded to achieve the extraordinary performance of new engineering materials. This rapidly evolving area of science is necessarily interdisciplinary, as it combines fundamental physics, chemistry and biology with geoplanetary and materials science, in addition to increasingly becoming one of the keys to engineering and technology aimed at process optimisation. Current experimental methods permit materials to be studied at pressures of several megabars, temperatures of tens of thousands of degrees Kelvin, and to achieve magnetic fields of several thousand teslas. Moreover, the rapid surge in computer technology has, in turn, permitted the solution of many previously intractable problems, and now even allows the behaviour of matter to be predicted far beyond the range of conditions currently accessible to experimentation. Previously unknown phenomena such as the formation of new phases, new forms of electronic and magnetic order, melting, atomic and electronic excitation, ionisation or the formation of a plasma state might result from exposing matter to extreme conditions well beyond those which were characteristic of the equilibria at the time of formation. With this volume of EMU Notes in Mineralogy we have endeavoured to provide up-to-date reviews of our understanding of the behaviour of minerals and geomaterials at exterior conditions that are sufficiently extreme to induce changes. In total 18 chapters reflect the diversity of this theme, but also demonstrate how strongly interdisciplinary this domain of modern mineralogy has become, bringing together physicists, chemists and geologists as well as experimentalists and computer scientists. The present volume contains the contributions of the lectures presented at the 7th EMU School, held at the University of Heidelberg from June 19 to June 25, 2005.