From semiconductor to Fermi metal and emergent density-wave-like transition in the quasi-one-dimensional n-type Bi19S27I3 under hydrostatic pressure

We report on crystal growth and physical properties of the quasi-one-dimensional compound Bi19S27I3 by combining crystal structure, electrical resistivity, magnetic properties, Seebeck coefficient, Hall coefficient as well as hydrostatic pressure effect up to 11.5 GPa. Unlike n-type Bi19S27I3 crystals, the maximum size of high-quality p-type Bi19S27I3 crystals can reach 2-3 mm by optimizing the chemical vapor transport method. The measurement results indicate that Bi19S27I3 is a diamagnetic semiconductor with two thermal activation energies, a large one E-g1 similar to 0.81 eV and a small one E-g2 similar to 0.36 eV, a huge room-temperature Seebeck coefficient of -1000 mu V/K, and improved thermoelectric power factor similar to 2.2 mu W cm(-1) K-2 owing to the enhanced electrical conductivity. Under pressure, Bi19S27I (3)undergoes a semiconductor-to-metal transition, and the thermal activation energy continuously decreases to almost zero near a critical pressure of 4.25 GPa. Accompanying this process, a density-wave-like transition emerges, characterized by the reversible jump observed in the temperature dependence of the resistivity. As the pressure further increases, the resistivity undergoes a crossover from a Fermi metal to a low-temperature upturn below a characteristic temperature, which decreases from 81 K at 4.5 GPa to 37 K at 11.5 GPa. The upturn in resistivity has a linear dependence on the logarithmic temperature, but does not saturate at low temperatures, which basically excludes a Kondo-like state and indicates the possibility of Anderson weak localization. High-pressure synchrotron x-ray diffraction confirms the absence of structural transition for P<12.05 GPa at room temperature, supporting pressure-induced electronic transition. Our density functional theory calculation on the assumption that the Bi1 occupies an average of similar to 1/6 contradicts experimental electron bands, indirectly indicating that Bi1 should be partially ordered and has many vacancies in Bi19S27I3. Our results provide good examples for studying the mechanism of semiconductor metallization and exploring thermoelectric functional properties in low-dimensional materials