AMORPHIZATION AND PHASE-TRANSFORMATION OF NIOBIUM PENTOXIDE BY FINE GRINDING

The mechanical amorphization process of Nb//2O//5 was studied. After vibro-milling well crystallized Nb//2O//5 in the H-phase for 6 h with an amplitude 20 mm, its X-ray diffraction pattern turned into a halo pattern. On prolonged grinding, however, X-ray diffraction peaks reappeared. They belonged to a new phase (TT-phase), formed as a consequence of structural restabilization. By grinding with an amplitude 50 mm, however, no halo pattern was found on the X-ray diffractogram. Instead, apparently direct phase transformation from H-phase into TT-phase was observed even after grinding for only 5 min. The effect of amplitude on the mechanochemical structural changes is discussed in relation to the crystallographical structure of Nb//2O//5. The disorderly states of mechanically amorphized and hydrolysed materials were very alike, judging from the radial distribution function. It is therefore concluded, that a non-crystalline material very similar to a synthesized one could be obtained through a mechanical route by choosing an appropriate condition of stressing.