On the size dependence of the critical point of nanoscale interstitial solid solutions

It is shown that a size dependence of the critical temperature T-c of the m iscibility gap in nanocrystalline and nanoscale particle interstitial solid solutions results from stress owing to elastic interaction of the bulk wit h layers of material at the grain boundaries or surfaces which have a small solute susceptibility (i.e. a weak dependence of the concentration on the chemical potential) at the phase transition. When the volume Fraction occup ied by the interfacial layers is not too large, then the changes in T-c and in the critical. concentration x(c) can be predicted on the basis of a ser ies expansion of the solute chemical potential in the bulk about the critic al point. The model can be extended to free-standing thin films and coheren t multilayers. The dependence of the pressure on the hydrogen concentration in the crystal lattice of nanocrystalline palladium-hydrogen is measured o n the basis of X-ray diffraction data. The result agrees with the predictio ns of the theory.