Transition metal dichalcogenides (TMDs) have recently gained tremendous interest for use in electronic and optoelectronic applications. Unfortunately, the electronic structure or band gap of most TMDs shows noncontinuously tunable characteristics, which limits their application to energy-variable optoelectronics. Thus, layered materials with better tunability in their electronic structures and band gaps are desired. Herein, we experimentally demonstrated that layered WSe2 possessed highly tunable transport properties under various pressures, with a linearly decreasing band gap that culminates in metallization. Pressure tuned the band gap of WSe2 linearly, at a rate of 25 meV/GPa. The high tunability of WSe2 was attributed to the larger electron orbitals of W2+ and Se2– in WSe2 compared to the Mo2+ and S2– in MoS2. WSe2 underwent an isostructural phase transition from a 2D layered structure to a 3D structure at approximately 51.7 GPa, where a conversion from van der Waals (vdW) to covalent-like bonding was observed in the valence electron localization function (ELF). Our results present an important advance toward controlling the band structure of layered materials and suggest significant implications for energy-variable optoelectronic devices via pressure engineering.

The structure transition sequence follow M1 → M'1 → X, the PIM in M′1 phase occurs at 43.2 GPa and mainly driven by electron-correlation.

The structure transition sequence of W–VO2(R) nanoparticles follows rutile (R) → orthorhombic (CaCl2-type) → monoclinic (Mx) within metallic phases.

Pressure-induced phase transitions of monoclinic H-Nb 2 O 5 have been studied by in situ synchrotron x-ray diffraction, pair distribution function (PDF) analysis, and Raman and optical transmission spectroscopy. The initial monoclinic phase is found to transform into an orthorhombic phase at ~9 GPa and then change to an amorphous form above 21.4 GPa. The PDF data reveal that the amorphization is associated with disruptions of the long-range order of the NbO 6 octahedra and the NbO 7 pentagonal bipyramids, whereas the local edgeshares of octahedra and the local linkages of pentagonal bipyramids are largely preserved in their nearest neighbors. Upon compression, the transmittance of the sample in a region from visible to near infrared (450-1000 nm) starts to increase above 8.0 GPa and displays a dramatic enhancement above 22.2 GPa, indicating that the amorphous form has a high transmittance.The pressure-induced amorphous form is found to be recoverable under pressure release, and maintain high optical transmittance property at ambient conditions. The recoverable pressure induced amorphous material promises for applications in multifunctional materials.