Abstract
The elastic stability of the bcc and fcc alkali metals is studied theoretically over wide ranges of hydrostatic pressure P. A pseudopotential model is employed to compute the variations of the bulk moduli \ensuremath{\kappa} and shear moduli \ensuremath{\mu} and \ensuremath{\mu}\ensuremath{'}, as well as the differences between the Gibbs energies of the two structures. Stability is assessed according to the criteria of Hill and Milstein, i.e., \ensuremath{\kappa}(P)\ensuremath{\gtrsim}0, \ensuremath{\mu}(P)\ensuremath{\gtrsim}0, and \ensuremath{\mu}\ensuremath{'}(P)\ensuremath{\gtrsim}0. In compression, the stability ranges of both phases are controlled primarily by the shear modulus \ensuremath{\mu}, and high pressure bcc\ensuremath{\rightarrow}fcc transitions in K, Rb, and Cs are found to be associated with the vanishing of this modulus. The ``interplay'' between the ranges of elastic stability and thermodynamic phase equilibrium (at 0 K) is also studied. \textcopyright{} 1996 The American Physical Society.
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