X-Ray Scattering of Unusual Order Fluctuations in the $\alpha$, ${\alpha }^{\prime }$ Phase of $\mathrm{Nb}{\mathrm{H}}_x$

We report x-ray measurements on $\mathrm{Nb}{\mathrm{H}}_x$ single crystals, at high temperatures. In addition to the strong fundamental ($\mathrm{hh}0$) x-ray reflections, weak intensity peaks were observed at the $\frac{1}{2}\left(hh0\right)$ positions ($h$ odd). The intensity of these weak peaks increases with H concentrations. It is proposed that the experimental results come from periodic distortions of the Nb host lattice, in regions with partial ordering of hydrogen atoms in every second (110) plane, caused by pretransitional fluctuations of the low-temperature ordered $\zeta$-phase ${\mathrm{Nb}}_2$ H.