High-pressure phase transition and metallization in Ar(H2)2

The high-pressure phase transition and the metallization of Ar(H-2)(2) are investigated using first-principles methods. A phase transition from the experimentally observed MgZn2 structure to a CeCu2-type structure is predicted near 66 GPa. This phase transition provides a possible explanation for the disappearance of the Raman active vibron mode in experiment between 55 and 70 GPa. The metallization of the CeCu2 structure is promoted by the intermolecular interactions among H-2 molecules, but hindered by the modulation of Ar atoms. The competition between these two mechanisms implies that the pressure for metallization in Ar(H-2)(2) is higher than that suggested for pure hydrogen. This prediction is a result of an examination of a previous proposal that hydrogen could metallize at much lower pressure by mixing with Ar, and provides insight for future studies on metallization of hydrogen through the use of hydrogen-rich mixtures.