  Applying elastic deformation can tune a material physical properties locally
and reversibly. Spatially modulated lattice deformation can create a bandgap
gradient, favouring photo-generated charge separation and collection in
optoelectronic devices. These advantages are hindered by the maximum elastic
strain that a material can withstand before breaking. Nanomaterials derived by
exfoliating transition metal dichalcogenides TMDs are an ideal playground for
elastic deformation, as they can sustain large elastic strains, up to a few
percent. However, exfoliable TMDs with highly strain-tunable properties have
proven challenging for researchers to identify. We investigated 1T-ZrS2 and
1T-ZrSe2, exfoliable semiconductors with large bandgaps. Under compressive
deformation, both TMDs dramatically change their physical properties. 1T-ZrSe2
undergoes a reversible transformation into an exotic three-dimensional lattice,
with a semiconductor-to-metal transition. In ZrS2, the irreversible
transformation between two different layered structures is accompanied by a
sudden 14 % bandgap reduction. These results establish that Zr-based TMDs are
an optimal strain-tunable platform for spatially textured bandgaps, with a
strong potential for novel optoelectronic devices and light harvesting.
