Nanocomposites and nanomaterials

Quantum Nature of Abnormal Stability of Calcium Apatite Structure
Karbovska L.I., Karbivskyy V.L., Kurgan N.A.
G.V. Kurdymov Institute for Metal Physics of the NAS of Ukraine,
03680, blvd. Vernadsky, 36, Kiev, Ukraine 
E-mail: karb@imp.kiev.ua  

The expansion of practical applications of apatites is mainly due to the features of the atomic and electronic structure, in particular, the anomalous stability of the structure of calcium apatite in a wide range of non-stoichiometry (Ca/P varies from 1.34 to 1.72). Therefore, understanding the nature of the mechanisms for the stability of the structure of apatite and the fundamental principles of organization and management of the physicochemical properties of apatite-like structures based on calcium is possible only if the role of the emerging d-shell of calcium in the compounds is described, depending on the composition, synthesis conditions, changes in the size and topology of key elements, as well as a detailed analysis of the electronic structure of calcium apatites.
The role of the nascent d-shell of calcium in the formation of the anomalous features of calcium apatite depending on the composition, synthesis conditions, changes in dimensionality and topology of key elements is investigated. An analysis of the electronic structure of calcium apatite is performed with spectral and quantum-mechanical methods. The limitations of the application of quantum-mechanical calculations using the methods of the density functional theory to the description of the long-range component of the interaction of calcium with the surroundings are established. In turn, experimental data indicate that the stability of the structure of apatite is determined largely by the two-valley effective potential of calcium d-electrons. In various calcium compounds, atomic effects play a significant role in forming the shape of the Lα-spectra of calcium, and, as a result, the participation of d-states of calcium in bond formation is levelled by their significant localization, apparently, in the inner valley of the effective potential.