Photoemission study of the electronic structure of silver palladium alloys

Photoemission experiments have been made on a series of AgPd alloys including the pure components. In Ag-rich alloys the d levels of the Pd atoms occupy a resonant bound state which has a width similar 1 eV at infinite dilution increasing to similar 1.7 eV at 30% Pd. It is argued that a major contribution to this breadth at infinite dilution is the spin orbit splitting of the d levels; the resonance broadening, 2? on the Anderson model, being estimated as 0.5 eV. The increase in breadth with increasing Pd content is attributed to interatomic d-d broadening between Pd atoms. The isolated impurity atom is believed to possess similar 0.38 d holes and contribute to the density of states at the Fermi level an amount similar 0.185 eV-1 per atom. These values are compatible with other properties of AgPd alloys namely the electron specific heat and residual electrical resistance. Comparison is made with the analogous CuNi alloys. Above 40% Pd the d electrons occupy true band states and it is suggested that the transition from the resonant bound state to the band state is sharp and may be characterized as a semiconductor-metal transition for the Pd d electrons. The experimental data clearly show the effects of structural disorder on the sharp band structures of the pure components. In the case of PdAg alloys the blurring of the band structure due to disorder and the transference of electrons from Ag conduction to Pd d states on account of the weak screening of the Ag impurity atoms account for the rapid decrease in electron heat and paramagnetic susceptibility of Pd due to alloying with Ag. Direct transitions between conduction band states, capital Lambda1-capital Lambda1 transitions, were observed in pure Ag and the Ag0.95Pd0.05 alloy.