Biomedical subjects

Vladislav A Blatov

Publications and source records attributed to Vladislav A Blatov.

3 recordsLinked to original sources

PubMed2006

Analysis of migration paths in fast-ion conductors with Voronoi-Dirichlet partition.

In terms of the Voronoi-Dirichlet partition of the crystal space, definitions are given for such concepts as ;void', ;channel' and ;migration path' for inorganic structures with three-dimensional networks of chemical bonds. A number of criteria are proposed for selecting significant voids and migration channels for alkali cations Li+-Cs+ based on the average characteristics of the Voronoi-Dirichlet polyhedra for alkali metals in oxygen-containing compounds. A general algorithm to analyze the voids in crystal structures has been developed and implemented in the computer package TOPOS. This approach was used to predict the positions of Li+ and Na+ cations and to analyze their possible migration paths in the solid superionic materials Li3M2P3O12 (M=Sc, Fe; LIPHOS) and Na1+xZr2SixP3-xO12 (NASICON), whose framework structures consist of connected M octahedra and T tetrahedra. Using this approach we determine the most probable places for charge carriers (coordinates of alkali cations) and the dimensionality of their conducting sublattice with high accuracy. The theoretically calculated coordinates of the alkali cations in MT frameworks are found to correlate to within 0.33 A with experimental data for various phases of NASICON and LIPHOS. The proposed method of computer analysis is universal and suitable for investigating fast-ion conductors with other conducting components.

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PubMed2006

A method for hierarchical comparative analysis of crystal structures.

A geometrical-topological description of crystal structure as a three-dimensional graph with coloured nodes, weighted and coloured edges is used to generate a hierarchical sequence of the structure representations. The solid angles of Voronoi-Dirichlet polyhedra of atoms are used as the edge weights and the nodes and edges are coloured according to chemical reasons. Two operations are defined to derive the representations: contracting an atom to other atoms keeping the local connectivity, and removing an atom together with all its bonds. The atoms of the crystal structure are called origin, removed, contracted or target according to their roles in the operations. Each structure representation is described as a labelled quotient graph and determined by (i) colours of the graph nodes and edges, (ii) some level for edge weights, and (iii) an arrangement of atoms according to their roles. The computer enumeration and topological comparative analysis of all representations for crystal structures of any composition and complexity are implemented into the TOPOS program package. The advantages of the method are shown by the analysis of typical inorganic compounds and a molecular packing.

Journal Article↗

PubMed2004

Sizes of molecules in organic crystals: the Voronoi-Dirichlet approach.

The sizes of more than 100,000 molecules in organic crystals have been assessed as the volumes of molecular Voronoi-Dirichlet polyhedra. The average molecular volumes for all crystals are shown to be nearly equal to the corresponding values in homomolecular (consisting of identical molecules) crystals. The validity of the Voronoi-Dirichlet approach in determining molecular sizes is substantiated and the reasons for the variations in the molecular volumes are discussed. It is shown that a molecule increases its volume if it is surrounded by a good deal of high-row (i.e. an element with more than ten protons) atoms or if there is disorder in the crystal structure.

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