In one embodiment, a system includes a pressure cell adapted for enclosing a porous structure; an inert pressure medium within the pressure cell; and a heat source for heating the porous structure. In another embodiment, a composition of matter includes a crystalline porous structure having a density of about 30 to about 50 mg/cm.sup.3. A method according to one embodiment includes positioning an amorphous porous structure in a pressure cell; injecting an inert pressure medium within the pressure cell; and pressurizing the pressure cell to a pressure that thermodynamically favors a crystalline phase of the porous structure over an amorphous phase of the porous structure to transition the amorphous porous structure into a crystalline porous structure. Additional embodiments are also presented.
 The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC for the operation of Lawrence Livermore National Laboratory.