Vibrational line broadening in the mixed solid N2-Kr: A high-pressure Raman study of the phase diagram

In this paper, the results of an experimental study on the spectral behavior of the Raman Q branch of nitrogen in the mixed solid N2–Kr are presented. The experiments have been performed at ambient temperature as a function of pressure up to 15 GPa. On the basis of the results, the p-x cross section of the phase diagram is constructed. In the mixture, the β region extends to very high pressures. The maximum amount of krypton dissolving in β-nitrogen is about 85%. As a consequence, the regions where the fcc-Kr lattice and the δ lattice of nitrogen are stable are relatively small. In all phases, the vibrational frequencies of the nitrogen molecule are shifted to lower values compared with neat nitrogen. The most interesting aspect is that in the β solid the line width is extremely composition dependent, with maximum values for the mixture with equal mole fractions. It is suggested that the increase in the line width is mainly due to an increase in the correlation time rather than an increase of the amplitude of modulation