The thermodynamics of CaSiO3 in Earth's lower mantle

Abstract

The lower mantle of Earth, characterized by pressures of 24-127 GPa and temperatures of 1900-2600 K, is still inaccessible to direct observations. In this work, we investigate by first principles the stability, phase diagram, elastic properties, and thermal conductivity of CaSiO3, that constitutes a significant component of Earth's lower mantle. Notably, our simulations capture in full the anharmonic ionic fluctuations arising from the extreme temperatures and pressures of the lower mantle, thanks to the use of stochastic self-consistant harmonic approximation (SSCHA). We show that the cubic phase of CaSiO3 is the stable state at the lower mantle's thermodynamic conditions. The phase boundary between the cubic and tetragonal phases is of first-order and increases linearly from 300 K to 1000 K between 12 GPa and 100 GPa. Accounting for temperature-renormalized phonon dispersions, we evaluate the speed of sound as a function of depth. Our results downplay the role of octahedral rotations on the transverse sound velocity of cubic CaSiO3, advocated in the past to explain discrepancies between theory and experiments. The lattice thermal conductivity, assessed thanks to the recently introduced Wigner formalism, shows a predominance of particle-like transport, thus justifying the use of the standard Boltzmann transport equation even in a system with such strong ionic anharmonicity.

Main text: 7 pages, 4 figures. Supplemetary information: 4 pages, 3 figures

References in corpus (17)

• Restoring the density-gradient expansion for exchange in solids and surfaces
• Generalized gradient approximation for solids and their surfaces
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Distribution of phonon lifetime in Brillouin zone
• Observation of second sound in graphite at temperatures above 100 K
• The Stochastic Self-Consistent Harmonic Approximation: Calculating Vibrational Properties of Materials with Full Quantum and Anharmonic Effects
• Thermodynamics and dielectric response of ${\text{BaTiO}}_3$ by data-driven modeling
• Quantum phase diagram of high-pressure hydrogen
• Time-Dependent Self Consistent Harmonic Approximation: Anharmonic nuclear quantum dynamics and time correlation functions
• Crossover from Boltzmann to Wigner thermal transport in thermoelectric skutterudites
• Boltzmann Transport in Nanostructures as a Friction Effect
• Observation of phonon Poiseuille flow in isotopically-purified graphite ribbons
• First-principles thermodynamics of CsSnI3
• Wigner Gaussian dynamics: simulating the anharmonic and quantum ionic motion
• Microscopic picture of paraelectric perovskites from structural prototypes
• BTE-Barna: An extension of almaBTE for thermal simulation of devices based on 2D materials
• Deep-learning-based prediction of the tetragonal$\to$cubic transition in davemaoite

Cited by in corpus (1)

• Thermal transport in crystals: from the quantum Dyson equation to mesoscopic phonon hydrodynamics