Structural transition for positive impurity ions in fluids

It is suggested that the neighborhood of an alkaline-earth ion in a noble-gas fluid may undergo a structural transition as a function of applied pressure p0. For p0<pc, which depends on ion species and host fluid, a region of enhanced density surrounds the core ion. For p0>pc, a thin solid "crust" is present. The transition can be seen as a rapidly varying or discontinuous mobility at pc.