2005/05/30 by V. N. Bogomolov, V. Bogomolov, Bogomolov, V.
Environmental Science · Physics and Astronomy · #FOS: Physical sciences #Methane Hydrates and Related Phenomena #Superconductivity (cond-mat.supr-con) #cond-mat.supr-con
paper · pdf · doi:10.48550/arxiv.cond-mat/0505718
3 pages, 1 figure
arxiv created 2005/05/30 · openalex publication_date 2005/05/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
Traditionally, when one describes the crystallographic structure of oxides, the oxygen ion radius r02 is assumed to be approximately equal to 1.4A. The oxygen ions occupy in this case 80-90% of the crystal volume. Metal atoms are considered then as ions playing a role of donors with rather small radius of (0.5 - 0.8) A. However, the atomic packing picture and, therefore, physical properties such as electric conductivity and superconductivity of oxides will be essentially different, if we assume r02- ~ 0.56 A. Such magnitude of the radius is known from the quantum mechanics calculations [2]. According to this picture, 80-90 % of the crystal volume is occupied by the metal atom orbitals with radius (1.3-1.9) A, while the oxygen ions play a role of acceptors, which reduce occupancy of these orbitals ("indirect" dilution of the metal). A "direct" dilution of metals takes place in stoichiometric matrices. When r02-~0.56 A, channels with diameter 3.6 A present in the hexagonal matrix Ag3Pb2H2O6 directed along the "c" axis. The channels are filled by chains of the Ag2 molecules with atomic diameter of 2.6 A and the molecule concentration nB = 25.6 1020 cm-3. The Bose-Einstein condensation (BEC) temperature TcB ~ 400K is calculated for the electron effective mass value m*=7.5me, where me is the isolated electron mass. Three-dimensional networks of Na2 chains form in Na solutions in NH3 and WO3 as well (respectively, with nB=4.71 1020 cm-3; Tc sim 180K; m*=5.0me and nB=4.74 1020 cm-3; Tc sim 91K; m*=10me). Close magnitudes of the Ag2 and Na2 chains parameters respectively in NH3 and WO3 favors the opinion that all these structures have a composite structure and similar mechanisms of the high temperature superconductivity.