Structure of Liquid Aluminum Oxide

Abstract

The total structure factor, $S(Q)$, and the corresponding radial distribution function, $G(r)$, for supercooled and stable liquid aluminum oxide have been measured with x-ray synchrotron radiation. The specimens were levitated in a conical nozzle and melted with a laser, achieving temperatures in the range of 2200--2700 K. The first two peaks in $S(Q)$ reveal intermediate-range order and dense random packing of atoms, similar to that observed in many network liquids. The first two peaks in $G(r)$ are consistent with ${\mathrm{AlO}}_{4}^{5\ensuremath{-}}$ structural units and show that A${\mathrm{l}}_{2}$${\mathrm{O}}_{3}$ undergoes a major structural rearrangement on melting with an Al coordination change from octahedral to tetrahedral. The structure does not change appreciably with temperature in the stable and supercooled liquid. Implications of these results are discussed in connection with the solidification of aluminum oxide.