This article explores structural phase transitions in two-dimensional (2D) Mo- and W-dichalcogenide monolayers. The study reveals that mechanical deformations can switch the thermodynamic stability between a semiconducting and a metallic crystal structure in these materials. Using advanced density functional and hybrid Hartree-Fock/density functional calculations, the researchers identify MoTe₂ as a promising phase change material. They find that tensile strains of 0.3–3% are required to transform MoTe₂ under uniaxial conditions at room temperature. The potential for mechanical phase transitions is predicted for all six studied compounds. The study highlights the unique properties of group VI TMD monolayers, which can have more than one crystal structure, unlike graphene and hexagonal BN. One of these structures is semiconducting, while others are metallic. This polymorphism allows for the coexistence of metallic and semiconducting regions, which can be used for electronic devices and catalytic applications. The TMD metal-to-insulator transition is structural, leading to considerable metastability and hysteresis, which is valuable for nonvolatile information storage. The research also investigates the phase diagrams of TMD monolayers under different thermodynamic conditions. It finds that equibiaxial tensile strains of 10–15% are required to observe the metallic phase for most TMDs, but MoTe₂ may transform under considerably less tensile strain, less than 1.5% under appropriate constraints. Mixed-phase regimes can be thermodynamically stable under certain conditions. The study uses density functional theory (DFT) and DFT-based methods to determine the phase diagrams of TMD monolayers as a function of strain. It finds that the 2H and 1T' energy surfaces intersect for sufficiently large strains, and the changes in a and b required to change the relative energies U of the 2H and 1T' phase range from 13% (MoS₂) to 3% (MoTe₂). The results suggest that a transition between 2H and 1T' might be observable below but near the breaking threshold. The study also considers the effects of thermal corrections and hybrid functionals on the phase transitions. It finds that the use of the HSE06 functional brings the 2H-1T' threshold strains even closer to the origin. The research concludes that MoTe₂ is more suitable for technological applications due to its closer structural phase transition to ambient conditions. The findings suggest that mechanically induced phase transitions can be achieved using flexible substrates and other standard experimental approaches. This understanding is crucial for building our knowledge of the rich physics of 2D materials.This article explores structural phase transitions in two-dimensional (2D) Mo- and W-dichalcogenide monolayers. The study reveals that mechanical deformations can switch the thermodynamic stability between a semiconducting and a metallic crystal structure in these materials. Using advanced density functional and hybrid Hartree-Fock/density functional calculations, the researchers identify MoTe₂ as a promising phase change material. They find that tensile strains of 0.3–3% are required to transform MoTe₂ under uniaxial conditions at room temperature. The potential for mechanical phase transitions is predicted for all six studied compounds. The study highlights the unique properties of group VI TMD monolayers, which can have more than one crystal structure, unlike graphene and hexagonal BN. One of these structures is semiconducting, while others are metallic. This polymorphism allows for the coexistence of metallic and semiconducting regions, which can be used for electronic devices and catalytic applications. The TMD metal-to-insulator transition is structural, leading to considerable metastability and hysteresis, which is valuable for nonvolatile information storage. The research also investigates the phase diagrams of TMD monolayers under different thermodynamic conditions. It finds that equibiaxial tensile strains of 10–15% are required to observe the metallic phase for most TMDs, but MoTe₂ may transform under considerably less tensile strain, less than 1.5% under appropriate constraints. Mixed-phase regimes can be thermodynamically stable under certain conditions. The study uses density functional theory (DFT) and DFT-based methods to determine the phase diagrams of TMD monolayers as a function of strain. It finds that the 2H and 1T' energy surfaces intersect for sufficiently large strains, and the changes in a and b required to change the relative energies U of the 2H and 1T' phase range from 13% (MoS₂) to 3% (MoTe₂). The results suggest that a transition between 2H and 1T' might be observable below but near the breaking threshold. The study also considers the effects of thermal corrections and hybrid functionals on the phase transitions. It finds that the use of the HSE06 functional brings the 2H-1T' threshold strains even closer to the origin. The research concludes that MoTe₂ is more suitable for technological applications due to its closer structural phase transition to ambient conditions. The findings suggest that mechanically induced phase transitions can be achieved using flexible substrates and other standard experimental approaches. This understanding is crucial for building our knowledge of the rich physics of 2D materials.