Materials with more non-metallic bonding are brittle, but are widely used, for instance as protective coatings. These often fail by cracking, so if their fracture resistance were increased, by making plastic flow easier, their lifetime could be extended. Some non-metallic materials deform readily, on a limited number of crystal planes, such as the ternary carbide Ti3SiC2 as well as Nb2Co7, W2B5 and Ta4C3. However, at present the understanding of how to design crystal structures for easy plastic flow is guided only by desirable ratios of elastic constants. Here, it is shown that flow is predicted to become very much easier if there are electronegativity differences within a crystal's unit cell, which cause non-uniform elastic deformation. Very substantial changes in flow behavior appear possible, suggesting this is a first step in developing a simple way of controlling plastic flow in non-metallic crystals.
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