A ceramic was developed that becomes more electrically conductive under elastic strain and less conductive under plastic strain. The material could lead to a new generation of sensors embedded into structures like buildings, bridges, and aircraft able to monitor their own health.
The electrical disparity fostered by the two types of strain was modeled as a novel two-dimensional compound called graphene-boron-nitride (GBN). Under elastic strain, the internal structure of a material stretched like a rubber band does not change. But the same material under plastic strain — caused in this case by stretching it far enough beyond elasticity to deform — distorts its crystalline lattice. GBN shows different electrical properties in each case, making it a worthy candidate as a structural sensor.
Hexagonal-born nitride (white graphene) can improve the properties of ceramics. Adding graphene makes them even stronger and more versatile, along with their surprising electrical properties.
The magic lies in the ability of two-dimensional, carbon-based graphene and white graphene to bond with each other in a variety of ways, depending on their relative concentrations. Though graphene and white graphene naturally avoid water, causing them to clump, the combined nanosheets easily disperse in a slurry during the ceramic’s manufacture. The resulting ceramics would become tunable semiconductors with enhanced elasticity, strength, and ductility.
Graphene is a form of carbon known for its lack of a band gap — the region an electron has to leap to make a material conductive. With no band gap, graphene is a metallic conductor. White graphene, with its wide band gap, is an insulator. So, the greater the ratio of graphene in the 2D compound, the more conductive the material will be. Mixed into the ceramic in a high enough concentration, the 2D GBN would form a network as conductive as the amount of carbon in the matrix allows. That gives the overall composite a tunable band gap that could lend itself to a variety of electrical applications.
Other 2D sheets with molybdenum disulfide, niobium diselenide, or layered double hydroxides may provide similar opportunities for the bottom-up design of tunable, multifunctional composites.