In order to determine the structure of this compound, an elec- tron diffraction pattern was obtained on one fiber, and is displayed in Fig. 1. The diffraction pattern with clear spots did not change as the electron beam was moved along the nanobelt, indicating that the whole nanobelt is a single crystal with a preferential growth along the [010] direction. The SAED pattern can be indexed to a monoclinic unit cell with the approximate parameters a=11.59Å, b=3.65Å, c=11.45Å, and b=95.47°. From the SAED pattern, the absence of (010), (100) is consistent with the extinc- tion rule h + k = 2n + 1, suggesting a face-centered monoclinic structure. This is all consistent with a d-phase material of compo- sition HxV4O10