Bandgap engineering in quasi-1D Zr1−xTixS3 (0 ≤ x ≤ 1) solid solutions

Abstract

TiS₃ and ZrS₃ are quasi-one-dimensional materials from the family of transition metal trichalcogenides with the general composition MX₃, where M is a transition metal and X is a chalcogen. Although isostructural, TiS₃ and ZrS₃ have very different bandgaps of approximately 1 eV and 2 eV, respectively. Consequently, Zr_1−xTi_xS₃ solid solutions are promising for achieving a composition-dependent bandgap that is tunable across a broad spectral range, from visible to infrared, for various electronic and optoelectronic applications. Previous studies demonstrated the synthesis of Zr_1−xTi_xS₃ solid solutions from elemental precursors at 800 °C, but only in a narrow compositional range of 0 ≤ x ≤ 0.33, while higher Ti content led to the formation of a secondary TiS₂ phase. In this work, we optimized the synthetic conditions and produced the entire range of Zr_1−xTi_xS₃ solid solutions (0 ≤ x ≤ 1) via a direct reaction between Zr–Ti alloys and sulfur vapor at a lower temperature of 600 °C. All Zr_1−xTi_xS₃ compositions crystallized as needle-like structures within the P2₁/m space group, with lattice parameters increasing with the Zr content, as confirmed by X-ray diffraction analysis. The optical bandgaps of the prepared crystals were within the 1 to 2 eV range and also increased with the Zr content, demonstrating that synthesis of Zr_1−xTi_xS₃ solid solutions is a viable route for bandgap engineering in transition metal trichalcogenides.