Synthesis of an Antiferromagnet Ba7Fe6S14 with One-dimensional Chains Constituted by FeS4 Tetrahedra

Compounds with chain structures have received great attention due to their unique quasi-one-dimensional charge transport channel which usually leads to striking physical phenomena. Here, we report the synthesis and detailed physical properties of Ba7Fe6S14 single crystals whose crystalline structure is featured by one-dimensional chains constituted by units of FeS4 tetrahedra. Susceptibility measurements reveal three magnetic phase transitions located at T = 10.5 K, 38 K, and 121 K. Further heat capacity measurements suggest a second-order phase transition for the transition at 121 K. At ambient pressure, the compound is an insulator with a large thermal activation energy around 0.19 eV. Application of pressure can gradually suppress the insulating behavior, and pressure-induced insulator-metal transitions can be achieved for P ≥ 21.3 GPa. No superconductivity was observed with pressure up to 47 GPa. Nevertheless, the unique chain-like structure of Ba7Fe6S14 provides chances for comparative studies with the quasi-one-dimensional spin-ladder iron-based superconductor BaFe2S3 for exploring the relation among crystalline dimensionality, magnetism, and superconductivity.