Thermoelastic properties of ringwoodite (Fex,Mg1-x)2SiO4: Its relationship to the 520 km seismic discontinuity

We combine density functional theory (DFT) within the local density approximation (LDA), the quasiharmonic approximation (QHA), and a model vibrational density of states (VDoS) to calculate elastic moduli and sound velocities of gamma-(Fe-x,Mg1-x)(2)SiO4 (ringwoodite), the most abundant mineral of the lower Earth's transition zone (TZ). Comparison with experimental values at room-temperature and high pressure or ambient-pressure and high temperature shows good agreement with our first-principles findings. Then, we investigate the contrasts associated with the beta ->gamma(Fe-x,Mg1-x)(2)SiO4 transformation at pressures and temperatures relevant to the TZ. This information offers clearly defined reference values to advance the understanding of the nature of the 520 km seismic discontinuity. (C) 2012 Elsevier B.V. All rights reserved.