Structure of alumina glass

The fabrication of novel oxide glass is a challenging topic in glass science. Alumina (Al₂O₃) glass cannot be fabricated by a conventional melt-quenching method, since Al₂O₃ is not a glass former. We found that amorphous Al₂O₃ synthesized by the electrochemical anodization of aluminum metal shows a glass transition. The neutron diffraction pattern of the glass exhibits an extremely sharp diffraction peak owing to the significantly dense packing of oxygen atoms. Structural modeling based on X-ray/neutron diffraction and NMR data suggests that the average Al-O coordination number is 4.66 and confirms the formation of OAl₃ triclusters associated with the large contribution of edge-sharing Al-O polyhedra. The formation of edge-sharing AlO₅ and AlO₆ polyhedra is completely outside of the corner-sharing tetrahedra motif in Zachariasen's conventional glass formation concept. We show that the electrochemical anodization method leads to a new path for fabricating novel single-component oxide glasses.