Thermal Conductivity of CaSiO₃ Perovskite at Lower Mantle Conditions

Thermal conductivity (κ) of mantle minerals modulates strongly both the style of mantle convection and the time scale of the Earth’s mantle and core cooling. It is therefore a fundamental parameter for geodynamic modeling. Cubic CaSiO₃ perovskite (cCaPv) is believed to be the third most abundant mineral in the lower mantle (LM) (7 vol%). However, despite its importance, investigations of its properties are challenging because of its strong anharmonicity. cCaPv is dynamically unstable at low temperatures and its phonon spectrum has imaginary frequencies from harmonic phonon calculation. Particularly for κ, prevailing theoretical approaches such as perturbative methods encounter difficulties in dealing with such strong anharmonicity. Experimental measurements at relevant high pressures and temperatures are equally challenging. Therefore, no previous estimate of cCaPv’s κ exists at mantle conditions, experimental or theoretical. Here we present ab initio quantum mechanical results of this property obtained using an established phonon quasiparticle approach that can address the strongly anharmonic situation in cCaPv. These results are substantiated by direct experimental measurements of this property at LM conditions. These results and data agree very well and reveal a surprisingly large κ of cCaPv compared to MgSiO₃-perovskite, which is only weakly anharmonic.