The Mott transition is primarily characterized by an isostructural insulator-metal transition in a correlated system under pressure, which is at the heart of many emergent phenomena. The associated transition mechanism, however, has been a long-standing challenge. Here we present a study of the mechanism underlying Mott transition in $\mathrm{PbCr}{\mathrm{O}}_3$ by exploring its bonding and electronic behaviors under pressure, which involves intricate lattice-charge interactions. We find that its Mott transition is mainly dictated by the Cr–O sublattice with largely tunable electronic and elastic properties under tensile stress, as exerted by the contracted Pb–O sublattice due to the presence of bond-length mismatch. Pressure can effectively balance tensile stress in the Cr–O sublattice for shortening its bond to a critical length, at which the $\mathrm{Cr}3d\text{–O}2p$ covalent hybridization occurs to form strong Cr–O bonds with a profoundly enhanced stiffness. As a response, extra bond shrinking spontaneously takes place to drive $3d$-electron delocalization and lattice collapse for the Mott transition. In addition, the electronic stability and structural symmetry of this material are also revealed to be closely related to its valence-electron density. These discoveries provide powerful insights into the atomistic mechanism of the Mott transition, which could also be applicable for understanding structural transitions in many other perovskite compounds.

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• Chemical bonding
• Phase transitions
• Pressure effects
• Structural properties