Electronic topological transition and phase transition in rhodium and iridium based inter metallic compounds

Of the Rh3Y, Rh3La, Ir3Y and Ir3La inter-metallic compounds, the compound Rh3Y exists in hexagonal structure, Ir3Y and Ir3La exist in rhombohedral structure, whereas the compound Rh3La exists in both hexagonal and rhombohedral structures. Based on our tight binding-linear muffin tin orbital (TB-LMTO) study of other rhodium and iridium-based Rh3X and Ir3X (where X=Ti, Zr, Hf, V, Nb, Ta and Sc) inter-metallic compounds of AuCu3 type cubic structure, an attempt is made to examine whether the compounds Rh3Y, Rh3La, Ir3Y and Ir3La will undergo a structural phase transition to cubic structure from their experimentally reported structures. From our study, it is observed that the compounds Rh3Y and Rh3La undergo a structural phase transition to cubic phase at 4.5 and 10.1 GPa, respectively, from their experimentally reported hexagonal and rhombohedral phases. Further it is predicted that both the compounds Ir3Y and Ir3La can exist in the cubic phase itself at ambient condition, in contrary to the experimental observation. From the band structure outputs that have been plotted for the compounds under compression, it is observed that the compounds Rh3La, Ir3Y and Ir3La undergo the Lifshitz type of transition which may change the Fermi surface topology and hence the physical properties of these compounds.