Quasi-thermodynamic model on hydride formation in palladium-hydrogen thin films: Impact of elastic and microstructural constraints

A thermodynamic model is proposed to deduce the H-H interaction energy EHH and an effective critical temperature Tceff of hydride formation in films. It allows for occasionally observed sloped plateaus of μH below Tceff. EHH (between 15 and 30 kJ/molH) and Tceff (340 K to 490 K) are reduced by up to 50% compared to bulk (EHH=36.8kJ/molH, Tc = 563 K), for all films. Concentration-dependent contributions of substrate-induced stress (of about (2-5) kJ/molH) and microstructure (of about (5-8) kJ/molH) are separated. For all films phase separation is still found at 300 K.