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Journal of Physical Studies 11(3), 298–302 (2007)
DOI: https://doi.org/10.30970/jps.11.298 ELECTRONIC STRUCTURE AND CHEMICAL BONDS IN COMPOUNDS OF THE HOMOLOGICAL HgBa2Can-1CunO2n+2+δ SERIESR. Lutciv, Ya. Boyko
Ivan Franko National University of Lviv, |
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The electronic density distributions in crystals of mercury homological series HgBa$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{2n+2+δ}$ ($n=1-4$) are investigated with the purpose of explaning earlier revealed features of non-stoichiometry and equilibrium properties of Hg-based high-temperature superconductors (HTSC). The distributions $ρ(\rm{r})$ are received as a result of band structure calculations by full-potential extension of a linear muffіn-tіn-orbitals method in local density approximation. The obtained distributions demonstrate the non-monotonic change of chemical bond character at the increase in the amount of $\rm{CuO_{2}}$ planes in elementary cells of series members, with the maximal value of a covalency in the HgBa$_{2}$Ca$_{2}$Cu$_{3}$O$_{8}$ compound. The observed increasing in electronic density between mercury atoms and apical oxygen with increasing of $n$ from 1 up to 3 can be interpreted as a weak change of the chemical bond character from ionic to covalent with return change at the transition to a member with $n{=}4$. The revealed peculiarities correlate with superconducting properties of the studied materials and can serve as confirmation of one of the carriers pairing models in HTSC, based on the mixed ionic-covalent character of the chemical bond in $\rm{CuO_{2}}$ plane and according to which superconductivity is realized on the asymmetric delocalized $π$-bond. A special value of the Hg-O(A) bond in the formation of the superconducting properties of Hg-based HTSC is confirmed as well.
PACS number(s): 74.25.Jb, 74.72.Jt