Adsorption-desorption isotherms and x-ray diffraction of Ar condensed into a porous glass matrix

Ar condensed into a porous glass matrix has been investigated by simultaneous measurements of adsorption-desorption isotherms and x-ray diffraction patterns as function of the pore filling above and below the melting point. The chemical-potential--temperature phase diagram has been established. It is consistent with a first-order phase transition between the adsorbate state and the capillary condensed state, above and below the melting temperature. The adsorbate and the capillary condensed state can also be distinguished in the diffraction patterns. A consistent picture of the structure and the thermodynamics is obtained.