Quantum-mechanical calculation of the solid-state equilibrium MgO+α-Al2O3MgAl2O4 (spinel) versus pressure

M. Catti, G. Valerio, R. Dovesi, and M. Causà
Phys. Rev. B 49, 14179 – Published 15 May 1994
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Abstract

The ground-state crystal energies of cubic MgAl2O4 (spinel) and MgO (periclase) and of rhombohedral α-Al2O3 (corundum) have been calculated at different volumes, relaxing the corresponding structures, by all-electron periodic Hartree-Fock methods (crystal program). Basis sets of contracted Gaussian-type functions are employed for the 18 atomic (including d) orbitals representing each of the Mg, Al, and O atoms. Mulliken net atomic charges zMg=1.86‖e‖ (MgO), zAl=2.30‖e‖ (α-Al2O3), zMg=1.74‖e‖, and zAl=2.24‖e‖ (spinel) are obtained. The elastic bulk modulus, the Murnaghan equation of state p(V) at the athermal limit, the Mg-O and Al-O bond compressibilities, and the binding energy have been derived for each phase (and the elastic constants C11 and C12 for spinel only). Comparison with existing experimental data is discussed. The enthalpy change for spinel decomposition into the simple oxides has been computed as a function of pressure, including a correction for the electron correlation energy based on local-density-functional theory. A decomposition pressure of 11 GPa at T=0 K is predicted, against values of 8 and 13 GPa derived from experimental thermodynamic data and from direct compression experiments, respectively.

  • Received 28 January 1994

DOI:https://doi.org/10.1103/PhysRevB.49.14179

©1994 American Physical Society

Authors & Affiliations

M. Catti and G. Valerio

  • Dipartimento di Chimica Fisica ed Elettrochimica, Università di Milano, via Golgi 19, 20133 Milano, Italy

R. Dovesi and M. Causà

  • Dipartimento di Chimica Inorganica, Fisica e dei Materiali, Università di Torino, via Giuria 5, 10125 Torino, Italy

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Vol. 49, Iss. 20 — 15 May 1994

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