TETRAGONAL STATES FROM EPITAXIAL STRAIN ON METAL-FILMS

The tetragonal states produced by isotropic pseudomorphic epitaxial st rain in the (001) plane on a tetragonal phase of a crystal are calcula ted for V, Ti, Rb, Li, K, and Sr from first-principles electronic theo ry. It is shown that each metal has two tetragonal phases correspondin g to minima of the total energy with respect to tetragonal deformation s (and hence are equilibrium phases) and that the equilibrium phases a re separated by a region of inherent instability. The equilibrium phas e for any strained tetragonal state can thus be uniquely identified. L attice constants and relative energies of the two phases and the saddl e point between them are tabulated, as well as the tetragonal elastic constants of each phase.