Correlation between structural stability and electronic structure of f Electron based intermetallic compounds under pressure

Abstract

In this thesis, an attempt has been made to correlate the structural stability and the electronic structure of several f-electron based intermetallic compounds (f-IMCs). The work consists mainly of high pressure X-ray diffraction experiments, electronic structure calculations along with the generation of empirical 2-D structural stability maps. High pressure X-ray diffraction experiments up to 30 GPa have been carried out. The results show that UGa3 system is stable up to 30 GPa. Electronic structure calculations have been carried out as function of reduced volume up to 40 GPa. The results show that the Fermi level lies very close to the maximum in the DOS curve. In order to validate the result of 2-D maps, total energy of the system has been calculated for hexagonal structure and compared with total energy curve of cubic AuCu3 type structure. Although, the energies of these two structures are very close, the total energy curve of AuCu3 type structure lies below that of Ni3Sn. This comparison shows that AuCu3 cubic type structure is more stable than Ni3Sn (hexagonal) type structure. This may be due to the large range of structural stability of AuCu3 type structures under pressure. In order to understand the structural stability of LaAl2 and LaAl3 compounds, the band structure calculations as a function of reduced volume have been carried out. The density of states of LaAl2 reveals that the EF lies in a slope between bonding maxima and antibonding minima. The value almost equal to one is known as condition for stability. And also, the value of Wocc/Wb do not show any change under pressure in both the cases. The band dispersion curves for both the compounds show movement to f bands under the influence of pressure. Some of them cross the Fermi level leading to so called Lifshitz transitions. However, it is seen that these electronic changes do not manifest in any volume anomaly in the compound under pressure. This may be due to the fact that the bands touching the EF are mostly sp in nature with low density of state