Structure-Spin-Transport Anomaly in Quasi-One-Dimensional Ba₉Fe₃Te₁₅under High Pressure

Recently, a series of novel compounds Ba3MX5 (M = Fe, Ti, V; X = Se, Te) with hexagonal crystal structures composed of quasi-1-dimensional (1D) magnetic chains has been synthesized by our research team using high-pressure and high-temperature methods. The initial hexagonal phases persist to the maximum achievable pressure, while spin configurations and magnetic interactions may change dramatically as a result of considerable reductions in interchain separations upon pressurization. These compounds therefore offer unique possibilities for studying the evolution of intrinsic electronic structures in quasi-1D magnetic systems. Here we present a systematic investigation of Ba9Fe3Te15, in which the interchain separations between trimerized 1D chains (∼ 10.2 Å) can be effectively modulated by external high pressure. The crystal structure especially along the 1D chains exhibits an abnormal expansion at ∼5 GPa, which accompanies trimerization entangled anomalous mixed-high-low spin transition. An insulator-metal transition has been observed under high pressure as a result of charge-transfer gap closing. Pressure-induced superconductivity emerges at 26 GPa, where the charge-transfer gap fully closes, 3D electronic configuration forms and local spin fully collapses.