Systematic of polymorphous transformation of crystals, generalized on the base of M.J. Burger’s criteria

Abstract

The paper proposes an extended (3\xa0×\xa03) classification of polymorphous transformations, which includes the 0 th \xa0coordination sphere in addition to the M.\xa0J.\xa0Burger’s I and II coordination spheres. As a\xa0result, the first parameter of this classification is the number of a\xa0transformable coordination sphere\xa0— it takes the value equal to 0 (atom, ion), 1 (the coordination polyhedra) and 2 (the nearest to the coordination polyhedra environment). The second parameter of the classification is determined by the Burger’s energy barrier for a\xa0transformation. And here, in addition to transformations with a\xa0break of chemical bonds (reconstructive) and without it (deformational), some intermediate types of transformations take place\xa0— with a\xa0disordering of structural units (atoms, molecules and other atomic complexes). As examples of polymorphous transformations with transformation of\xa0the\xa00 th \xa0coordination sphere, there are considered electron transitions in an atom, changes of the atom’s spin, and magnetic ordering of atoms in a\xa0crystal structure. Transformations with disordering are illustrated by substitutions-jumps of structural units and their slowed down or free rotation. There is developing the concept of “polymorphism” of chemical elements.