Thickness dependence of the critical solution temperature of hydrogen in Pd films

Abstract

The isotherms of very thin PdHx films (60 Å<d<600 Å) have been determined below room temperature by equilibrium potential measurements. One finds that the critical temperature Tc is lowered when the film thickness decreases: for the 60-Å film Tc would be near 173 K. This marked drop of Tc is attributed to clamping effects of the sample on the substrate, which decreases the effective H–H interaction and favors short-range coherency effects.

Electrochemical modeling of hydrogen storage in hydride-forming electrodes

“…9b). The phase diagram is in the good agreement with previous results (see [8,[21][22][23][24]). The phase boundaries x˛and xč onverge smoothly towards a single phase-transition point which we denote, on the analogy of the critical temperature and critical composition [36] as the critical layer thickness.…”

“…The phase boundaries x˛and xč onverge smoothly towards a single phase-transition point which we denote, on the analogy of the critical temperature and critical composition [36] as the critical layer thickness. The critical layer thickness of this Pd-system where the miscibility gap has completely vanished is at about 10 nm and can, very likely, be related to clamping of the thin films onto the substrate, similarly as concluded before [24]. …”

“…[22,23] the critical temperature of phase transition decreases as a function of film thickness. While the former results were obtained from gas-phase experiments, the electrolytic (de)hydrogenation is decribed in [24]. The significant drop of the critical temperature with decreasing film thickness was attributed to clamping effects of the film to the substrate.…”

Hysteresis and the single-phase metal-insulator transition in switchableYHxfilms

“…For example, it has been shown for palladium that the reduced film thickness has a marked effect on the thermodynamic phase diagram; for thin films the critical temperature appears to be lowered considerably, indicating a weakening of the elastic H-H interaction energy. 5,6 The discovery of switchable mirrors based on rare earth metal hydrides (RH x ) was another result of the use of thin films in the study of M H x systems. Huiberts et al 7 showed that hydrogen absorption in yttrium and lanthanum induces a metal-insulator transition accompanied by drastic optical changes; the initially reflecting metal transforms into a transparent insulator.…”

Mg-Based Thin Films as Model Systems in the Search for Optimal Hydrogen Storage Materials

“…The large impact on the thermodynamics was observed for rigid substrates which cause resistance toward volume expansion [29,30]. The increase of peq due to the stresses caused by capping layer or a substrate would be very desirable with respect to practical application if these stresses would not relax after few hydrogen absorption/desorption cycles drawing back the peq to its original value.…”