Cristalografia

Appl. Phys. A 89, 813–823 (2007) DOI: 10.1007/s00339-007-4223-2

Applied Physics A
Materials Science & Processing

j.-l. hodeau1,u r. guinebretiere2

Crystallography: past and present∗
1 2

Institut NEEL, C.N.R.S./U.J.F., BP166 X, 38042 Grenoble Cedex, France Lab. Science des Proc´ d´ s C´ ramiques et de Traitements de surface SPCTS, ENSCI, e e e 87065 Limoges, France

Received: 1March 2007/Accepted: 25 June 2007 Published online: 28 September 2007 • © Springer-Verlag 2007
ABSTRACT In the 19th century, crystallography referred to the study of crystal shapes. Such studies by Ha¨ y and Brau vais allowed the establishment of important hypotheses such as (i) “les mol´ cules int´ grantes qui sont cens´ es etre les plus pee e e ˆ tits solides que l’on puisse extraire d’un min´ral” [1], (ii) the e definition of the crystal lattice and (iii) “le cristal est clivable ` parall` lement a deux ou trois formes cristallines” [2]. This more phological crystallography defined a crystal like “a chemically homogeneous solid, wholly or partly bounded by natural planes that intersect at predetermined angles” [3]. It described the main symmetry elements and operations, nomenclatures ofdifferent crystal forms and also the theory of twinning. A breakthrough appeared in 1912 with the use of X-rays by M. von Laue and W.H. and W.L. Bragg. This experimental development allowed the determination of the atomic content of each unit cell constituting the crystal and defined a crystal as “any solid in which an atomic pattern is repeated periodically in three dimensions, that is, any solid that“diffracts” an incident X-ray beam” [3]. Mathematical tools like the Patterson methods, the direct methods, were developed. The way for solving crystalline structure was opened first for simple compounds and at that time crystallography was associated mainly with perfect crystals. In the fifties, crystallographers already had most apparatus and fundamental methods at their disposal; however, we hadto wait for the development of computers to see the full use of these tools. Furthermore the development of new sources of neutrons, electrons and synchrotron X-rays allowed the studies of complex compounds like large macromolecules in biology. Nowadays, one of the new frontiers for crystallographers is to relate the crystal structure to its physical-chemical-biological properties, this meansthat an accurate structural determination is needed to focus on a selective part of the structure (chemical order, anisotropy, charge transfer, magnetic order) versus an external parameter like temperature, pressure, magnetic or electric field. Modern crystallography is also extended to the study of very small crystals, powders, ill-ordered or non-crystallized materials. Thus presently,crystallography is concerned with any solid that “scatters” an incident beam. Nevertheless, as quoted by A. Guinier, “the problems facing crystallographers have only changed, ... new ones have appeared which require reflection and imagination, ... and which in turn may still bring much joy to all those who like crystallography” [4].

Such developments open up crystallography to modern materials like artificialones and nanostructures with low- and/or multi-scaled-periodicities and/or extremely small “crystal size” and to materials of the “real world”, with mixtures of phases and/or amorphous contribution and/or defects, a common characteristic of ancient materials analysed in patrimonial research. In our contribution we will show by selected examples that these improvements were allowed (i) by the useof powerful sources, apparatus and detectors which allow micro-diffraction, in-situ diffraction, spectroscopy, resonant scattering, inelastic scattering, coherent scattering, (ii) by the development of methods like diffraction anomalous fine structure (DAFS), pair distribution function (PDF), simulated annealing, single object reconstruction, (iii) by combination of scattering and spectroscopy...