Completely Elastic Deformation of Hydrogenated Ta Thin Films

Nanostructured metal hydrides could play a key role in a hydrogen economy. The nanostructuring or confine-ment of these materials as, e.g., thin films significantly affects the structural and functional properties. For tantalum hydride, a versatile hydrogen sensing material, we show that the confine-ment of tantalum as a thin film extends the solubility limit by suppressing the phase transition observed in bulk upon hydrogenation. Different from bulk, the body centered cubic unit cell continuously deforms with unequal lattice constants and angles between lattice vectors. This deformation ensures that the volumetric expansion is realized in the out-of-plane direction, and surprisingly, completely elastic in nature. The first-order phase transition suppression combined with the continuous elastic deformation of the tantalum unit cell over an extraordinary wide solubility range ensures the superb performance of tantalum and its alloys as a hysteresis-free optical hydrogen sensing range over a hydrogen pressure/concentration range of over 7 orders of magnitude.

Automated summary

Nanostructured metal hydrides have a crucial role in a hydrogen economy, as the nanostructuring or confinement of these materials significantly affects their structural and functional properties. We demonstrate that confining tantalum as a thin film extends its solubility limit, suppressing the phase transition observed in bulk upon hydrogenation. The continuous elastic deformation of the tantalum unit cell with unequal lattice constants and angles ensures volumetric expansion in the out-of-plane direction, resulting in superb performance as a hysteresis-free optical hydrogen sensor over a wide hydrogen pressure/concentration range.