Crystallography is a science that examines the arrangement of atoms in solids. The word “crystallography” derives from the Greek krustallos meaning cold drop or originated in cold. A more current definition states that it is a science describing the atomic and molecular structure of solids and its relation to physical, chemical and biological properties. In 2014 we will celebrate 100 years since awarding the Nobel Price to Max von Laue for the experiments that for the first time revealed the atomic (crystal) structure of solid matter via X-ray diffraction. That is why the UNO announced the year 2014 to be the International Year of Crystallography. One of the basic thoughts in the search for a crystal structure is a presumption of its symmetry and of the periodic arrangement of its basic building elements – atoms, eventually molecules. Since we live in three-dimensional space, we intuitively – and usually correctly – understand three-dimensionally ordered structures. However, the improving experimental methods allowed us to discover that there is an important group of solids that deviate from this strict rule, while their properties are related to seemingly negligible deviations from the well-established order. With the help of electron density isolines in the Ta-Ge-Te alloy crystal the stamp shows that instead of the expected placement on the straight line, atoms positions are modulated so that they create a crenel, which ultimately results into the change of substance’s properties. The motive depicted in FDC shows such usage of symmetry that abstracts (from bottom to top) from a specific atoms arrangement in a kaolinite structure to symbolic schemes of OD theory that reflecting the laws of symmetry, lead to simplified and more understandable presentation. The stamp on FDC represents a fragment of such a structure. On commemorative sheet is a depiction of Laue diagram of a chromium compound crystal with a threefold symmetry axis in line with the primary X-ray beam. UV protective layer printed on surface of postage stamp is derived directly from Laue diagram depicted on Commemorative sheet which is finally stamped by commemorative cancellation dedicated to honour of Max von Laue.                                               

Dalma Gyepesová
Ľubomír Smrčok