Peculiarities of the electronic structure of calcium and strontium apatites

Abstract

The comparison of the calculated data of the total density of electronic states for a crystal elementary cell (LMTO-calculation) and cluster-calculation XO 4 3− of a tetrahedron has shown practical concordance of the form and main features of curves that indicates the determining role of nanofragment structures XO 4 3− tetrahedron in formation of the main features of calcium apatites total density of states. It is confirmed, that the electronic structure of stochiometric apatites systems is low sensitive to anions type (which is located along c-axis of crystal), right up to its elimination, that practically can be revealed in lability of apatite's structure relative to its position. The symmetry of XO 4 3− anion oscillations in a crystal lattice of apatite is determined not only by the symmetry of its local environment but also appreciably by the nature of chemical bonds X–O inside anion. The greatest influence on tetrahedral sublattice in calcium apatite renders ion Cl −, and in strontium apatite ion OH −. The symmetry of tetrahedrons in strontium fluorapatite is higher comparing to hydroxy- and chlorapatite. The indirect interaction metal–metal is observed in metal sublattice. This interaction occurs mainly between atoms in Ca (2) positions with participation of oxygen hydroxyl group atoms. The channel of interaction Ca (2)–O (3)–Ca (1) through of oxygen atoms from PO 4 − groups is observed thus less expressed. The interaction of ions Ca (2) with hydroxyl in hydroxyvanadate is much weaker, than in hydroxyapatite. It is shown, that in the formation of the L α-spectra form curve of calcium in calcium apatites the significant role is played by the nuclear effects and, as consequence, the participation of d-states of calcium in formation of bond is graded by their significant localization, most likely in an internal valley of effective potential.