The powder X-ray pattern of the dried electrospun material is presented in Fig. 2, together with those taken after heat treatment at 550 °C and 850 °C (Fig. 2b and c). As expected, the as-spun material shows only three broad bands, at ~21°, ~44.5° and ~83.5°, with no signs of diffraction peaks, which indicates its amorphous nature. On the contrary, in the heat treated samples only diffraction lines characteristic for the cubic Yb2O3 can be seen, with unit cell parameters a550=10.4399(2) and a850=10.4360(1) Å for heat treatments at 550 °C and 850 °C, respectively, that AGN 205728 agree with those previously reported . It can be seen that the samples treated at different temperatures have comparable cell parameters. However, both values are slightly larger than the values reported for the bulk material. Similar behavior has been observed in other oxides, and explained by the presence of a larger concentration of oxygen vacancies  or by the reduction of the particle size, which results in an increase of the repulsive dipolar interactions at the surface of the particles due to the presence of unpaired electronic orbitals . Moreover, the samples treated at lower temperatures have significantly less intense and broader peaks when compared with those treated at higher temperatures. This reflects the influence of the heat treatment temperature on the crystallinity but also on the crystallite size of the prepared Yb2O3, as discussed below.