Ba2Ti2Fe2As4O: A New Superconductor Containing Fe2As2 Layers and Ti2O Sheets

We have synthesized a new oxypnictide, Ba2Ti2Fe2As4O, via a solid-state reaction under a vacuum. The compound crystallizes in a body-centered tetragonal lattice, which can be viewed as an intergrowth of BaFe2As2 and BaTi2As2O, thus containing Fe2As2 layers and Ti2O sheets. Bulk superconductivity at 21 K is observed after annealing the as-prepared sample at 773 K for 40 h. In addition, an anomaly in resistivity and magnetic susceptibility around 125 K is revealed, suggesting a charge- or spin-density wave transition in the Ti sublattice.我们通过真空固相反应合成了一种新型氧磷族化合物（oxypnictide）Ba₂Ti₂Fe₂As₄O。该化合物以体心四方晶格结晶，可视为BaFe₂As₂与BaTi₂As₂O的共生结构，包含Fe₂As₂层与Ti₂O片层。将制备态样品在773 K下退火40小时后，可观测到21 K时的体相超导电性。此外，在约125 K处观测到电阻率与磁化率出现反常行为，表明Ti亚晶格存在电荷或自旋密度波相变。