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Laboratories:  Inorganic Materials Sciences Chemistry of Coordination Compounds
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Superconductors

Russian

The discovery, in 2008, of superconductivity in fluorine-doped iron-lanthanum oxoarsenide LaFeAsO1-xFx (Fig. 1) with a critical temperature (Tc) of 26 K caused a tremendous interest in the scientific community. This discovery has initiated numerous studies on the properties of doped materials LnFeAsO1-xFx, as well as an intensive search for new superconducting materials among the related systems. The critical temperature raised to 55 K by the present time as a result of the significant progress in the synthesis and study of the properties of these substances. Four families of superconductors were obtained and characterized; thay are the so-called family of 1111 with the general formula LnOFeAs (Ln rare earth metal), the 122 family AEFe2As2 (AE = Ca, Sr, Ba and Eu (II)), the 111 family AFeAs (A = Li, Na), and the 011 family FeSe.

  1111   122
8.6 Å 7.0 Å
       
  111   011
6.3 Å 5.5 Å

Despite the diversity of chemical compositions, all known superconductors based on iron pnictides exhibit similarities in crystal structure, which is the presence of the so-called conductive layers of FeAs with antiflyuorite structure, which alternate with the positively charged layers (the so-called charge reservoirs) whose nature may differ. Altogether, this leads to a wide variety of compositions of superconductors. In the 1111 phases, such blocks have the fluorite structure (LnO); in 122 they are alkaline earth metal cations AE(2), in phases of the 111 family they are alkali metal cations Li and Na. For the appearance of superconductivity, typically, at least one of these layers should be doped, leading to either hole or electronic conduction. Under pressure, the superconducting properties show up in the undoped 1111 and 122 phases.

The extraordinary diversity of chemical composition of the superconducting pnictides and chalcogenides of transition metals makes the search for new representatives with higher Tc very promising. The laboratory staff actively working in this direction. Currently working on this subject two graduate students and three postgraduate students, the three diploma works were successfully defended.

For inquired: Dr. I.V. Morozov .

Last updated: 25.11.2013 23:27:10


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