SrFe2As2

SrFe2As2, also called strontium iron arsenide, is an iron-based compound belonging to the 122 family of pnictides. It crystallizes in the body-centered tetragonal ThCr2Si2-type structure (space group I4/mmm) at room temperature, with alternating Sr layers and Fe2As2 layers. Lattice parameters are approximately a = 3.92 Å and c = 12.36 Å.

Electronic and magnetic properties: The material is metallic and undergoes a coupled structural and magnetic transition around 200 K. In the high-temperature phase it is paramagnetic and tetragonal; below the transition it adopts an orthorhombic structure and exhibits stripe-type antiferromagnetic order on the Fe sublattice, with Fe moments of order 0.8–1 μB.

Superconductivity: The undoped parent compound is not superconducting. Superconductivity can be induced by chemical substitution (hole doping via Sr → K, e.g., Sr1−xKxFe2As2, Tc up to about 37 K; electron doping via Fe site substitution, e.g., SrFe2−xCoxAs2, Tc up to around 20 K) and by applying hydrostatic pressure (reports of superconductivity at several gigapascals with Tc up to ~25–30 K).

Related compounds and significance: SrFe2As2 is a member of the 122 iron pnictides and has been widely studied to understand the relationship between structural/magnetic transitions and superconductivity in iron-based superconductors. It is typically synthesized by solid-state reaction of Sr, Fe, and As under inert conditions and can form polycrystalline or single-crystal samples.