Internal Thermal Stress-Driven Phase Transformation in Van der Waals Layered Materials.

High pressure or strain is an effective strategy for generating phase transformations in van der Waals (vdW) layered materials without introducing defects, but this approach remains difficult to perform consistently. We present a scalable and facile method for achieving phase transformation in vdW materials, wherein solid vdW materials are subject to internal thermal stress within a molten metal mantle as it undergoes cooling. This internal thermal stress is principally the product of differential thermal expansion between mantle and core and can be tuned by the mantle material and temperature conditions. We validated this approach by achieving phase transformation of red phosphorus to black phosphorus, and metallic 1T'- to semiconducting 2H-MoTe crystals. We further demonstrate quantum electronic phase transformation of suppressed charge density wave in TiSe by means of electron-phonon coupling using the same system.