Revisiting Electronic Topological Transitions in the Silver-Palladium (AgPd) Solid Solution: An Experimental and Theoretical Investigation.

Multiple thick film samples of the AgcPd1-c solid solution were prepared using physical vapour deposition over a borosilicate glass substrate. This synthesis technique allows continuous variation in stoichiometry, while the distribution of silver or palladium atoms retains the arrangement into an on-average periodic lattice with smoothly varying unit cell parameters. The alloy concentration and geometry were measured over a set of sample points, respectively, via energy-dispersive X-ray spectroscopy and via X-ray diffraction. These results are compared with ab initio total energy and electronic structure calculations based on density functional theory, and using the coherent potential approximation for an effective medium description of disorder. The theoretically acquired lattice parameters appear in qualitative agreement with the measured trends. The numerical study of the Fermi surface also shows a variation in its topological features, which follow the change in silver concentration. These were related to the electrical resistivity of the AgcPd1-c alloy. The theoretically obtained variation exhibits a significant correlation with nonlinear changes in the resistivity as a function of composition. This combined experimental and theoretical study suggests the possibility of using resistivity measurements along concentration gradients as a way to gain some microscopic insight into the electronic structure of an alloy.