Mechanical stability of Pd/Ti thin films during hydrogen (de)sorption at different applied partial pressure levels of hydrogen

Abstract

In this work, mechanical stability and kinetics of hydrogen (de)sorption of thin Palladium films (100 nm) magnetron sputter deposited on a magnetron sputtered Titanium intermediate layer were studied. In particular of two film morphologies, an open voided columnar morphology and a compact columnar morphology, the substrate-induced stress and its relaxation upon hydride formation were investigated at room temperature. By conducting in-situ X-ray diffraction (XRD) measurements combined with line-broadening analysis of the diffraction profiles, it was observed that the α (H-poor phase) to β (H-rich phase) transition induces stress that could (partially) relax by dislocation generation. After several absorption-desorption cycles (at 0.05 atm p(H2)), however, this stress increase prevents a full transformation to the β phase. When applying a higher partial pressure p(H2) = 0.1 atm for both of the selected open and compact-structured Pd/Ti thin films, a full phase transformation was observed. The corresponding phase transition kinetics, stress states and microstructural behaviors of the open and compact-structured Pd/Ti samples were found to be different. The microstructural changes and the kinetics of phase transformation during H2 (de)sorption are explained in terms of stress development and its relaxation through dislocation/defect generation.