Stability of simple cubic crystals

Although simple cubic (sc) crystals tend to be "inherently unstable" under ambient conditions, their potential stability is enhanced in states of pure hydrostatic tension, which can be approached locally near stress raisers such as cracks. Our molecular-dynamics simulations verify that a range of hydrostatic stress exists under which sc crystals are stable. Three distinct destabilization mechanisms are observed, depending on the bulk-modulus magnitude and the magnitude and algebraic sign of the shear modulus mu('), which in turn depend on the stress level; two of these mechanisms result in fracture, while the third yields a sc-to-hcp phase transformation by a unique two-stage shearing process. (c) 2007 American Institute of Physics.