Microscopic-macroscopic relationships in silicates: Examples from IR and Raman spectroscopy and heat capacity measurements
Charles A. Geiger, Boris A. Kolesov, 2002. "Microscopic-macroscopic relationships in silicates: Examples from IR and Raman spectroscopy and heat capacity measurements", Energy Modelling in Minerals, Carlo Maria Gramaccioli
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The field of lattice dynamics links the atomistic vibrational properties of a material to its macroscopic thermodynamic properties. In physics and chemistry lattice dynamic studies have been undertaken for a number of years, but, in comparison, relatively little work has been done in crystallography/mineralogy. This is partly a result of their historical development where the focus has been a determination of the static properties of crystal structures using primarily diffraction measurements. In addition, compositionally and structurally complex silicates that are of geochemical and geophysical interest are not easily amenable to lattice dynamic study. This situation in mineralogy has been changing and experimental vibrational spectroscopic and computational investigations are increasing in both number and scope. Although further study of the important silicate mineral groups is required before their vibrational properties are well described, good progress has been made in understanding many simple oxide and silicate structures. Atomistic and lattice dynamic study, when combined with the solid base of structural, crystal chemical and thermodynamic data that exists for silicates, enables prediction of mineral behaviour at different pressure and temperature conditions. In addition, it provides valuable insight that can be used to interpret or understand the macroscopic thermodynamic functions like heat capacity and bulk physical properties such as thermal expansion and elastic constants. These are cutting-edge research topics for mineralogists and mineral physicists and work in this general area is now an important part of mineral sciences. Accordingly, this book considers the energetic and lattice dynamic properties of Earth and planetary materials and, here
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The present book shows the arguments which have been considered in the EMU School (No. 4), dealing with Energy Modelling in Minerals; these arguments have been selected in order to provide examples of application of the most advanced theories to several cases. It should be pointed out that although the ultimate solution of our problems should involve “ab initio” quantum-mechanical calculations, at present such sophisticated procedures are far from being routine. Therefore, although “ab initio” approaches will play an ever-increasing role in the future and some important and most recent examples of such approaches are illustrated here, the greatest part of the contributions is dealing with empirical atom-atom calculations. Remarkably enough, such “semi-empirical” applications are often quite successful, providing excellent (or comparatively excellent) results in spite of their more or less approximate nature. It often happens that the methods here illustrated are some steps ahead of the current level of empirical treatment, thereby indicating a possible way of improvement by figuring out routines to be adopted in practice. If some methods seem to be too speculative to be actually usable, here they also are shown, in view of their possible discussion, or just to indicate a way to obtain promising developments. Among the descriptions of practical methods and results, some purely theoretical arguments have been inserted; these arguments — although abstract — according to our opinion are fundamental for earth scientists. Owing to the present status of the art, in a number of arguments there is no unique opinion with respect to their theoretical treatment as it is explained by different authors. Instead of having all of them discarded except the one which looks to be the most appropriate to the Editor (who might sometimes be personally involved in the question), most of such controversial points have been left just as they are, in the original draft of their advocates. Accordingly, the reader might find some discrepancies between some articles and others, which may lead to some obscurity; there are, however, several good reasons in favour of our behaviour. First of all, with a few exceptions we apologize about, our attention in inviting the contributors has been extended to all the principal authors in the world, with no limitation to a group of particular friends; moreover, the presence of different opinions in the context might give rise to interesting debates and critical objections; a further point is that the validity of the different treatments is shown per se by either the level of the theory and most of all by the agreement with the corresponding experimental data. Since we have to do with an advanced school, and in line with what should be a scientific procedure, it is important to provide the user with the possibility of choosing what seems to be the most appropriate method among a number of selected possibilities, rather than yielding to the assertion that something is indeed the ultimate and unquestionable “truth”.