Synthesis of photochromic oxygen-containing yttrium hydride

TL;DR

This study presents a method to synthesize photochromic oxygen-containing yttrium hydride through a two-step process, revealing structural and optical changes upon oxygen incorporation, with potential applications in smart coatings.

Contribution

It introduces a controlled oxygen incorporation process into yttrium hydride, demonstrating the resulting photochromic behavior and structural properties using in-situ analysis.

Findings

Oxygen incorporation causes a color change from dark to transparent.

The lattice parameter increases from 5.2 Å to 5.4 Å during oxygen reaction.

The non-reacted YHₓ is identified as YH₂ based on lattice measurements.

Abstract

Photochromic oxygen-containing yttrium hydride has been synthesized using a two step process. The process consists of an initial sputter deposition of oxygen-free yttrium hydride YH$_\mathrm{x}$, followed by a controlled reaction with air that causes incorporation of oxygen into the material. An in-situ study of the YH$_\mathrm{x}$ as it reacted with oxygen was made possible by applying an aluminium capping layer with a low but non-zero oxygen permeability prior to air exposure. During the reaction, the visual appearance of the YH$_\mathrm{x}$ went from dark and opaque to transparent and yellowish. This transition was accredited incorporation of oxygen into the material, as shown through analysis with energy dispersive x-ray spectroscopy (EDS) and x-ray photoemission spectroscopy (XPS). Grazing incidence x-ray diffraction (GIXRD) studies revealed an fcc structure both before and after oxygen exposure, with a lattice parameter that increased from 5.2 {\AA} to 5.4 {\AA} during the reaction. With the lattice parameter in the oxygen free YH$_\mathrm{x}$ being equal to that reported earlier for YH$_\mathrm{2}$, our findings suggest that the non-reacted YH$_\mathrm{x}$ in this study is in-fact YH$_\mathrm{2}$.