We develop the thermodynamic theory for the decomposition of a “coherent” two-phase open system consisting of an interstitial solid solution in equilibrium with a gas reservoir of solute atoms. It is shown that, contrary to what is expected for incoherent systems, the phase rule is inapplicable and the “plateau” on the pressure-composition isotherm does not correspond to two coexisting phases. The coherency strain introduces an unsurmountable macroscopic energy barrier between the transforming phases, which prevents the coexistence of the phases and results in a reversible hysteresis in the pressure-composition isotherm. The proposed theory is applicable to metal-hydrogen systems.

• Received 15 July 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.2523