Synthesis and Superconductivity of Ba 2 Ti 2 (Fe 1− x Cr x ) 2 As 4 O

Ba2Ti2(Fe1−x Cr x )2As4O (0 ≤ x ≤ 8%) compounds are synthesized by solid-state reaction and their structure and superconductivity are studied with x-ray diffraction, electric resistivity, and magnetization measurements. It is observed that the Cr dopants in the Fe site of Ba2Ti2Fe2As4O expand the lattice constants, but do not cause any structure phase transition. Superconducting transition temperature T c of the Ba2Ti2(Fe1−x Cr x )2As4O is found monotonically depressed with Cr doping level at an average depression rate of ΔT c /Cr − 1% = − 2.6 K. Meanwhile, the superconducting volume fraction is also significantly reduced, and the low-temperature resistivity is enhanced. It is believed that the Cr dopants work as pair-breaking impurities, which take responsibility for the depression of superconductivity in the system.