AUTHOR=Shi Caijuan , Alderman Oliver L. G. , Berman Diana , Du Jincheng , Neuefeind Joerg , Tamalonis Anthony , Weber J. K. Richard , You Jinglin , Benmore Chris J. 

TITLE=The Structure of Amorphous and Deeply Supercooled Liquid Alumina

JOURNAL=Frontiers in Materials

VOLUME=6

YEAR=2019

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2019.00038

DOI=10.3389/fmats.2019.00038

ISSN=2296-8016

ABSTRACT=<p>Liquid Al<sub>2</sub>O<sub>3</sub> has been supercooled more than 500 K below its melting point (<italic>T</italic><sub><italic>m</italic></sub> = 2,327 K) using aerodynamic levitation and laser heating techniques. High energy synchrotron x-ray measurements were performed over a temperature range of 1,817 ≤ T (K) ≤ 2,700 and stroboscopic neutron diffraction at 1,984 and 2,587 K. The diffraction patterns have been fitted with Empirical Potential Structure Refinement (EPSR) models and compared to classical Molecular Dynamics (MD) simulation results. Both sets of models show similar trends, indicating the presence of high populations of AlO<sub>4</sub> and AlO<sub>5</sub> polyhedral units predominantly linked by triply shared oxygen atoms. EPSR reveals that the mean Al–O coordination number changes linearly with temperature with <italic>n</italic><sub>AlO</sub> = 4.41 – [1.25 × 10<sup>−4</sup>] (<italic>T</italic> – <italic>T</italic><sub><italic>m</italic></sub>), with a 2.5 Å cutoff. Both EPSR and MD simulations reveal a direction of the temperature dependence of the aluminate network structure which moves further away from the glass forming ideal (<italic>n</italic><sub>AlO</sub> = 3) during supercooling. Furthermore, we provide new experimental data and models for amorphous alumina grown by sequential infiltration synthesis of a polymer template. The amorphous solid form likely has a larger Al-O coordination number than the liquid, consistent with expectations for the hypothetical glass.</p>