First-order structural phase transition in CaFe2As2

CaFe2As2 has been synthesized and found to form in the tetragonal ThCr2Si2 structure with lattice parameters a=3.912(68) angstrom and c=11.667(45) angstrom. Upon cooling through 170 K, CaFe2As2 undergoes a first-order structural phase transition to a low-temperature orthorhombic phase with a 2-3 K range of hysteresis and coexistence. This transition is clearly evident in microscopic, thermodynamic, and transport measurements. CaFe2As2 is the third member of the AFe(2)As(2) (A=Ba,Sr,Ca) family to exhibit such a dramatic phase transition and is a promising candidate for studies of doping induced superconductivity.