Structural collapse and Tc record in rare-earth-doped CaFe2As2

A team from the National Institute of Standards and Technology (NIST) and the University of Maryland has found an iron-based superconductor that operates at the highest known temperature for a material in its class. Iron-based superconductors, which were discovered only about four years ago, are a hot research topic, in part because they are more amenable to commercial applications than copper-based superconductors, which are more difficult to make and are frequently brittle. The iron-based superconductor CaFe2As2 is particularly promising because these superconductors` properties can be custom-tailored by substituting other atoms for these basic elements. Of perhaps greatest value to manufacturers is that its threshold temperature of superconductivity is 47 degrees Kelvin, the highest yet for the 1:2:2 class, whose previous record was 38K. It can superconduct at this record temperature when a smaller аliovalent rare-earth atom substitution into the alkaline-earth site of CaFe2As2 single crystals is performed, the overall crystal actually shrinks by about 10 percent, a dramatic size change.

Source: Phys. Rev. B 85, 024525 (2012)