We report on crystal growth and physical properties of the quasi-one-dimensional compound ${\mathrm{Bi}}_{19}{\mathrm{S}}_{27}{\mathrm{I}}_3$ by combining crystal structure, electrical resistivity, magnetic properties, Seebeck coefficient, Hall coefficient as well as hydrostatic pressure effect up to 11.5 GPa. Unlike $p$-type ${\mathrm{Bi}}_{19}{\mathrm{S}}_{27}{\mathrm{I}}_3$ crystals, the maximum size of high-quality $n$-type ${\mathrm{Bi}}_{19}{\mathrm{S}}_{27}{\mathrm{I}}_3$ crystals can reach 2–3 mm by optimizing the chemical vapor transport method. The measurement results indicate that ${\mathrm{Bi}}_{19}{\mathrm{S}}_{27}{\mathrm{I}}_3$ is a diamagnetic semiconductor with two thermal activation energies, a large one $E_{\mathrm{g}1}\sim 0.81$ eV and a small one $E_{\mathrm{g}2}\sim 0.36$ eV, a huge room-temperature Seebeck coefficient of −1000 µV/K, and improved thermoelectric power factor $\sim 2.2\mu \mathrm{W}\mathrm{c}{\mathrm{m}}^{-1}{\mathrm{K}}^{-2}$ owing to the enhanced electrical conductivity. Under pressure, ${\mathrm{Bi}}_{19}{\mathrm{S}}_{27}{\mathrm{I}}_3$ 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 $\sim \frac{1}{6}$ contradicts experimental electron bands, indirectly indicating that Bi1 should be partially ordered and has many vacancies in ${\mathrm{Bi}}_{19}{\mathrm{S}}_{27}{\mathrm{I}}_3$. Our results provide good examples for studying the mechanism of semiconductor metallization and exploring thermoelectric functional properties in low-dimensional materials.

• Received 21 November 2023
• Revised 2 February 2024
• Accepted 26 March 2024

DOI:https://doi.org/10.1103/PhysRevB.109.144107