High-pressure decomposition of MCr2O4 spinels (M=Mg, Mn, Zn) by ab initio methods |
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| Authors: | M Catti F Freyria Fava C Zicovich R Dovesi |
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| Institution: | (1) Dipartimento di Scienza dei Materiali, Università di Milano, via Emanueli 15, 20126 Milano, Italy, IT;(2) Dipartimento di Chimica Inorganica, Chimica Fisica e dei Materiali, Università di Torino, via Giuria 5, 10125 Torino, Italy, IT;(3) Instituto de Tecnología Química, U.P.V.-C.S.I.C., Av. Naranjos 5/n, 46022 Valencia, Spain, ES |
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| Abstract: | The high-pressure equation of state of the normal spinels MgCr2O4 (picrochromite), MnCr2O4 and ZnCr2O4, and their reaction of decomposition into Cr2O3 (eskolaite) and MO (rocksalt-type) component oxides, were investigated by periodic unrestricted Hartree-Fock calculations.
All-electron basis sets, and an a posteriori correction for the electron correlation energy, based on Density-Functional-Theory, were employed. Interpolation of results
by the P-V Murnaghan equation of state yielded the equilibrium volume and energy, and the bulk modulus and its pressure derivative,
for each of the seven phases (three spinels, three rocksalt oxides and eskolaite) considered. The simulated behaviour of interatomic
distances vs pressure shows similar compressibilities of M-O bonds in both octahedral and tetrahedral coordinations. Binding
energies and formation enthalpies of spinels from oxides are also computed and compared to available experimental data. The
predicted decomposition pressures of Mg, Mn and Zn chromium spinels are 19, 23 and 34 GPa, respectively. The greater stability
of ZnCr2O4 is related to Zn2+ being better suited to tetrahedral coordination than the other M2+ cations. Such results are strongly supported by the excellent agreement previously obtained between simulated (11 GPa) and
experimental (13 GPa) pressures of the decomposition of MgAl2O4 spinel into corundum and periclase.
Received: 9 February 1998 / Accepted: 12 October 1998 |
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| Keywords: | Spinels Chromium ab initio Calculation High-pressure decomposition |
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