Modulating the composition of a metal/oxide interface and using hydrogen as a probe

Strong irreversible traps for hydrogen atoms in internally oxidized Pd-3 at. % Al alloys are related to segregation at the Pd/Al/sub 2/O/sub 3/ phase boundaries. From an estimation of the strength of the binding energy, simple thermodynamic considerations, and sample preparation in an oxygen excess environment concluded that unsaturated oxygen bonds are present at the phase boundary and that the trapping corresponds to the formation of O-H bonds. For the case of Al-excess, oxygen bonds should be all saturated and Al-bonds remain unsaturated where no strong trapping of hydrogen expected in agreement with experiment. The case of free oxygen bonds at the interface and the irreversible trapping of hydrogen could be regained by annealing in air. Thus, hydrogen provides evidence that the composition of a phase boundary can be modulated depending on the chemical potentials of the species forming the compound.