International Journal of Physics | Vol. 3, No. 10, October 2012 | pp. 75–82
DOI: 10.46882/2012/IJP/000030
Research Article
Title: Elasticity and Vibrational Properties of Stishovite under Extreme Lower-Mantle Pressures
Names of Authors: L. M. Dupont¹, A. O. Awotunde²
Authors’ Affiliations: ¹Laboratoire de Geologie de Lyon, Ecole Normale Superieure de Lyon, 69364 Lyon, France; ²Department of Physics, University of Ibadan, Ibadan 200005, Nigeria
Abstract: Understanding the elastic and vibrational response behavior of silica polymorphs under high pressures is essential for interpreting deep-earth seismic profiles accurately. This research models the complete elastic tensor parameters and vibrational phonon modes of stishovite (SiO²). The calculations span hydrostatic pressure settings from 0 GPa up to 150 GPa. We used first-principles density functional theory (DFT) based on the generalized gradient approximation (GGA). The calculated data reproduce the well-known ferroelastic phase transition. This transition shifts stishovite from a tetragonal symmetry into a CaCl²-type orthorhombic crystal form at an identical pressure value of 52.3 GPa. This structural transition is driven directly by the softening of the B1g shear phonon vibrational mode. At the critical transition pressure point, the shear elastic modulus value C11 - C12 drops to 0 GPa. This drop causes a noticeable 24% reduction in transverse seismic wave propagation velocities. Our structural models indicate that this elasticity reduction explains the localized seismic reflector anomalies detected across the lower mantle region at depths near 1200 km. The calculated bulk modulus value at zero pressure is B0 = 302 GPa, with a pressure derivative value of B0' = 4.15. These values match experimental diamond anvil cell measurements within a minor 1.5% margin.
Keywords: Stishovite; density functional theory; phase transition; elastic moduli; soft phonon mode; lower mantle
Manuscript Timeline: Received: July 3, 2012; Revised: August 18, 2012; Accepted: September 4, 2012; Published: October 15, 2012
Citation: Dupont, L. M., & Awotunde, A. O. (2012). Elasticity and Vibrational Properties of Stishovite under Extreme Lower-Mantle Pressures. International Journal of Physics, 3(10), 75–82.
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