Nanostructured metal hydrides could play a key role in
a hydrogen
economy. The nanostructuring or confinement 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 confinement 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.