High-pressure stability, structure and compressibility of Cmcm?-MgAl2O4: an ab initio study |
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| Authors: | M Catti |
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| Institution: | (1) Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy Tel.: +39 02 64825139; Fax: +39 02 64825400 e-mail: catti@mater.unimib.it, IT |
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| Abstract: | Quantum-mechanical solid-state calculations have been performed on the highest-pressure polymorph of magnesium aluminate
(CaTi2O4-type structure, Cmcm space group), as well as on the low-pressure (Fd3ˉm) spinel phase and on MgO and Al2O3. An ab initio all-electron periodic scheme with localized basis functions (Gaussian-type atomic orbitals) has been used,
employing density-functional-theory Hamiltonians based on LDA and B3LYP functionals. Least-enthalpy structure optimizations
in the pressure range 0 to 60 GPa have allowed us to predict: (1) the full crystal structure, the pV equation of state and the compressibility of Cmcm-MgAl2O4 as a function of pressure; (2) the phase diagram of the MgO–Al2O3–MgAl2O4 system (with exclusion of CaFe2O4-type Pmcn-MgAl2O4), and the equilibrium pressures for the reactions of formation/decomposition of the Fd3ˉm and Cmcm polymorphs of MgAl2O4 from the MgO + Al2O3 assemblage. Cmcm-MgAl2O4 is predicted to form at 39 and 57 GPa by LDA and B3LYP calculations, with K
0=248 (K′=3.3) and 222 GPa (K′=3.8), respectively. Results are compared to experimental data, where available, and the performance of different DFT functionals
is discussed.
Received: 31 January 2001 / Accepted: 16 May 2001 |
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| Keywords: | MgAl2O4 polymorphs High pressure Ab initio calculations Compressibility |
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