IR spectroscopy as a tool for the characterisation of ceramic precursor phases
Anton Beran, Dietmar Voll, Hartmut Schneider, 2004. "IR spectroscopy as a tool for the characterisation of ceramic precursor phases", Spectroscopic methods in mineralogy, Anton Beran, Eugen Libowitzky
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Infrared (IR) spectra originate from transitions between vibrational energy levels of vibrating atomic groups and they are usually observed as absorption spectra. Molecules, atomic groups and even the whole lattice in crystals may interact with the electromagnetic field of light and absorb part of the energy carried by the light. The molecule interacts only with light that carries the right amount of energy to promote the molecule from one discrete energy level (ground state) to another. When it happens that IR radiation can be absorbed and a ground state molecule can be promoted to its first excited vibrational state, we say that the molecule has made a transition between the ground state and the excited state. Light of IR frequencies can generally excite molecules or functional atomic groups from one vibrational energy level to another. Hence, IR spectroscopy is called “vibrational spectroscopy”. Visible and UV radiation are higher energetic and can promote the redistribution of electrons in a molecule or atomic group, such that the electronic potential energy of the molecule is changed (“electronic spectroscopy”).
Using the terminology of quantum mechanics, we have to state that if a molecule is placed in an electromagnetic field (IR light), a transfer of energy from the field to the molecule will occur only when Bohr’s frequency condition is satisfied:
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Spectroscopic methods provide information about the local structure of minerals. The methods do not depend on long-range periodicity or crystallinity. The geometric arrangement of atoms in a mineral phase is only one aspect of its constitution. Its vibrational characteristic, electronic structure and magnetic properties are of greatest importance when we consider the behaviour of minerals in dynamic processes. The characterisation of the structural and physico-chemical properties of a mineral requires the application of several complementary spectroscopic techniques. However, it is one of the main aims of this School to demonstrate that different spectroscopic methods work on the same basic principles. Spectroscopic techniques represent an extremely rapidly evolving area of mineralogy and many recent research efforts are similar to those in materials science, solid state physics and chemistry. Applications to different materials of geoscientific relevance have expanded by the development of microspectroscopic techniques and by in situ measurements at low- to high-temperature and high-pressure conditions.