The synthesis and characterization of LiFeAs and NaFeAs

The newest homologous series of superconducting Fe-pnictides. LiFeAs (Li111) and NaFeAs (Na111) have been synthesized and investigated. Both crystallize with the layered tetragonal anti-PbFCI-type structure in P4/nmm space group. Polycrystalline samples and single crystals of Li111 and Na111 display superconducting transitions at similar to 18 K and 12-25 K. respectively. No magnetic order has been found in either compound, although a weak magnetic background is clearly in evidence. The origin of the carriers and the stoichiometric compositions of Li111 and Na111 were explored. (C) 2009 Elsevier B.V. All rights reserved.