  Order-disorder effects on equation of state (EOS) properties of
substitutional binary alloys are investigated with the cluster variation method
(CVM) based on ab initio effective cluster interactions (ECI). Calculations are
applied to the fcc based Ni-Al system. Various related quantities are shown to
vary with concentration around stoichiometry with a surprising "W shape", such
as the thermal expansion coefficient, the heat capacity and the Gruneisen
parameter, due to configurational ordering effects. Analysis shows that this
feature originates from the dominated behavior of some elements of the inverse
of Hessian matrix. For the first time we point out that the strong
compositional variation of these properties might be partially responsible for
local fractures in alloys and mineral crystals under heating, highlighting the
importance of subtle thermodynamic behavior of order-disorder systems.
