Joint diffraction and modeling approach to the structure of liquid alumina

The structure of liquid alumina at a temperature ∼2400 K near its melting point was measured using neutron and high-energy x-ray diffraction by employing containerless aerodynamic–levitation and laser-heating techniques. The measured diffraction patterns were compared to those calculated from molecular dynamics simulations using a variety of pair potentials, and the model found to be in best agreement with experiments was refined using the reverse Monte Carlo method. The resultant model shows that the melt is composed predominantly of AlO${}_4$ and AlO${}_5$ units, in the approximate ratio of 2:1, with only minor fractions of AlO${}_3$ and AlO${}_6$ units. The majority of Al-O-Al connections involve corner-sharing polyhedra (83$\%$), although a significant minority involve edge-sharing polyhedra (16$\%$), predominantly between AlO${}_5$ and either AlO${}_5$ or AlO${}_4$ units. Most of the oxygen atoms (81$\%$) are shared among three or more polyhedra, and the majority of these oxygen atoms are triply shared among one or two AlO${}_4$ units and two or one AlO${}_5$ units, consistent with the abundance of these polyhedra in the melt and their fairly uniform spatial distribution.