Raman spectra and phase behavior of the mixed solid N2-Ar at high pressure

The mixed solid N2-Ar has been studied for x[N2]=0.75, 130<T<470 K, and 0<p=20 GPa. A transition, very similar to the second order transition observed in pure d-N2, is still present in the mixed solid at 75 mol % N2. An anomalous increase of the slope in a p-T scan has been found, which is attributed to a redistribution of the Ar atoms near this transition. Although within the d* phase the Ar atoms are mainly located at the a sites, the distribution of the Ar atoms about the sites depends on temperature and pressure. Also at these high pressures the Ar atoms are able to move through the lattice. The inhomogeneous broadening of the vibrational signal in the d* phase has been observed also at low temperatures. The phase diagram of the mixture has been studied. The d-ß transition of pure N2 is shifted to lower temperatures in the mixture, while the ß-fluid transition is shifted to higher temperatures. The results are in agreement with computer simulations.