First-principles simulations of thermodynamical and structural properties of liquid Al2O3 under pressure

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First-principles molecular dynamics simulations within local density approximation were carried out for liquid alumina over a pressure range from 0 to 150 GPa at 3000, 4000, and 6000 K. Liquid alumina is more compressible and less dense than solid alumina, and the density difference between two phases decreases with compression with a density crossover occurring around 90 GPa at 3000 K. The calculated thermodynamic properties including specific heat, thermal expansion coefficient, and Grüneisen parameter are strongly pressure dependent. The liquid structure is more sensitive to compression than temperature: mean Al-O and O-Al coordination numbers which remain nearly unchanged on isochoric heating increase from 5.2 and 3.4, respectively, at 0 GPa to 6.8 and 4.5, respectively, at 150 GPa along 3000 K isotherm. Coordination environments consist of various species with low-coordination species (three- and four-coordinated Al atoms) disappearing and high-coordination species (six- and seven-coordinated Al atoms) appearing as the liquid is compressed. We also analyze the structure in terms of bond distances and bond angles. © 2011 American Physical Society.

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Physical Review B - Condensed Matter and Materials Physics

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