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Lattice dynamics and structural distortions of CaSiO 3 and MgSiO 3 perovskites
Author(s) -
Wolf George H.,
Jeanloz Raymond
Publication year - 1985
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl012i007p00413
Subject(s) - brillouin zone , materials science , lattice (music) , perovskite (structure) , phonon , molecular dynamics , condensed matter physics , mineralogy , thermodynamics , geology , crystallography , physics , chemistry , computational chemistry , acoustics
The phonon spectra, distortion mechanisms, and thermoelastic properties of CaSiO 3 and MgSiO 3 in the cubic perovskite structure are investigated as a function of pressure using a lattice dynamic approach. The bonding forces are derived from a parameter‐free rigid‐ion electron‐gas formulation. At low pressures, CaSiO 3 is found to be dynamically stable in the cubic perovskite structure; however, the phonon spectrum exhibits soft modes at the Brillouin zone boundary which ultimately result in a dynamic instability of the lattice near 80 GPa. The computed phonon spectrum of cubic MgSiO 3 perovskite exhibits complex frequencies along parts of the zone boundary at all densities investigated. These vibrational instabilities include coupled octahedral rotations which produce the observed distorted structure of MgSiO 3 perovskite. The measured bulk modulus of MgSiO 3 perovskite compares well with our calculated value for the cubic structure.