Diffraction techniques: Shedding light on structural changes at extreme conditions
Ronald Miletich, Clivia Hejny, Günter Krauss, Ullrich Angela, 2005. "Diffraction techniques: Shedding light on structural changes at extreme conditions", Mineral behaviour at extreme conditions, Ronald Miletich
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Following the discovery of X-ray scattering on crystalline materials, crystallography and the experimental application of diffraction techniques have resulted in our current understanding of the atomic arrangements and bonding in condensed phases.
Soon after Max von Laue’s famous experiments in 1912 (Fig. 1), for which he received the Nobel Prize in Physics in 1914, a period of pioneering work began. Starting with father and son Bragg in the early twenties, the “century of crystal-structure determination” brought insight to the atomic view of solid matter, which only had been a matter of speculation before the discovery of scattering by crystals. Scattering techniques were de-veloped over the subsequent years, not only using X-ray radiation, but also involving electron and neutron scattering phenomena. Nowadays, with the evolution of powerful radiation sources, such as neutron spallation sources or synchrotron radiation facilities, the nature of atomic structure can be visualised even for the most complex macromolec-ular systems which include thousands of atoms.
The pioneering work of structure solution was carried out at ambient conditions, starting with basic structures such as of sodium chloride, zincblende or diamond. Structure solution was not straightforward from the beginning. The so-called “phase problem”, i.e. the fact that the amount of phase shift on wave interference could not be determined experimentally from diffraction data, kept crystallographers busy for decades. It resulted in fundamental approaches, such as the Fourier summation of a set of squared (but not phased) amplitudes as introduced by A.L. Patterson (1934). H. Hauptman and J. Karle (1950) employed statistics and probability distributions as applied in the “direct methods” to overcome the phase problem.