Low-temperature synthesis of hydride semiconductor YH3-δ using Pt capped Y films and its chemical thermodynamics analysis

To decrease the temperature at which metallic yttrium (Y) reacts with H-2 to form the semiconductor trihydride phase, we employed Pt capping layers as catalysts, and compared the result with those obtained when employing Pd, Ni, or their co-capping layers. It was found that Pt capping with 5 nm thickness makes trihydride phase majority when hydrogenated at 27 degrees C, and allows us to obtain the trihydride phase with approximately 100% molar concentration when hydrogenated at 150 - 200 degrees C. Chemical thermodynamics analysis of the experimental results reveals that both the enthalpy and entropy differences between pure states of trihydride phase and dyhydride phase with hydrogen vapor show monotonic hydrogenation temperature dependencies with their sign inversions at approximately the same temperature around 150 degrees C, suggesting a particular thermodynamic mechanism specific to the hydrogen - yttrium system.