Progress in Cryocrystals at Megabar Pressures

Recent high-pressure studies of cryocrystals have provided a wealth of new information about the behavior of simple condensed-matter systems up to megabar (>100 GPa) pressures. Improved spectroscopic measurements with high-throughput spectrographs and chemically ultrapure synthetic diamonds, the extension of electrical conductivity measurements in the megabar pressure range, and several different X-ray diffraction methods made possible numerous new findings. Examples from rare-gas solids, solid hydrogen, and nitrogen are presented, and include pressure effects on many-body interactions, orthopara conversion rate, molecular orientational order-disorder, reconstructive transitions leading to the formation of new polymeric forms, and direct studies of pressure effects on shear strength.