EPR Study of Amorphous V$_{2}$O$_{5 }$From 125K -- 370K

Previous EPR spectra for V$_{2}$O$_{5}$ at low temperatures ($\sim $120K) reveal well-resolved resonances in which transitions are attributed to anisotropic hyperfine interactions. In contrast, recent results from our laboratory show EPR spectra with broad resonances that exist from 125K-370K with no apparent appearance of hyperfine interactions. EPR spin counting also indicates a high concentration ($\sim $10$^{20}$ spins/cm$^{3})$ of paramagnetic centers which suggests that the line widths are limited by spin-spin relaxation of the electron spin system. Current data reveal that EPR signal intensities increase more rapidly than (Temperature)$^{-1}$. In particular, a factor of $\sim $10 increase is seen when the temperature is decreased by a factor of 2. Possibilities for enhanced signal intensities include the presence of superparamagnetism or spin glass behavior. Current investigations are concerned with evaluations of a variety of EPR parameters over a temperature range from 125-370K.