Lattice Thermal Conductivity of MgSiO3 Perovskite from First Principles

Abstract

We investigate lattice thermal conductivity κ of MgSiO3 perovskite (pv) by ab initio lattice dynamics calculations combined with exact solution of linearized phonon Boltzmann equation. At room temperature, κ of pristine MgSiO3 pv is found to be 10.7 W/(m · K) at 0 GPa. It increases linearly with pressure and reaches 59.2 W/(m · K) at 100 GPa. These values are close to multi-anvil press measurements whereas about twice as large as those from diamond anvil cell experiments. The increase of k with pressure is attributed to the squeeze of weighted phase-spaces phonons get emitted or absorbed. Moreover, we find κ exhibits noticeable anisotropy, with κ zz being the largest component and being about 25%. Such extent of anisotropy is comparable to those of upper mantle minerals such as olivine and enstatite. By analyzing phonon mean free paths and lifetimes, we further show that the weak temperature dependence of κ observed in experiments should not be caused by phonons reaching ‘minimum’ mean free paths. These results clarify the microscopic mechanism of thermal transport in MgSiO3 pv, and provide reference data for understanding heat conduction in the Earth’s deep interior.

Ab initio lattice thermal conductivity of MgSiO3 across the perovskite-postperovskite phase transition

“…Here we rely on the frequency dependence of phonon linewidth [15,16,30,31] to interpolate 𝜏 𝐪+ in the BZ. Our previous studies show that both the quadratic relation, ~𝜔' , work for MgPv [15,16], yielding 𝜅 "#$ slightly lower and higher, respectively, than results obtained using the perturbative method with the same q-mesh [21]. Here, MgPPv's phonon linewidths phenomenologically follow very well the quadratic relation.…”

“…4(b). MgPv's 𝜏 𝐪+ and 𝑣 𝐪+ obtained with a comparably dense, 8 × 8 × 8 q-mesh [15,21] at the same P-T are also shown for comparison. At the P-T conditions considered here, MgPPv's average phonon lifetime, 𝜏̅ , is merely 10% longer than that of MgPv.…”

“…Besides, by computing anharmonic phonon dispersion, the obtained phonon velocities are also temperature-dependent. Such features are not present in the conventional perturbative methods to evaluate 𝜅 "#$ [10,20,21].…”

“…In principle, the phonon quasiparticle approach captures anharmonic interactions to infinite orders. Therefore, compared to the conventional perturbative methods [10,20,21] accounting for up to three-phonon scatterings, the present approach should yield more reliable phonon lifetimes at high temperatures where higher-order phonon-phonon scatterings arise. Besides, by computing anharmonic phonon dispersion, the obtained phonon velocities are also temperature-dependent.…”

The dependence of lattice thermal conductivity on phonon modes in pyrochlore‐related Ln2Sn2O7 (Ln = La, Gd)

“…In recent years, the first-principles phonon Boltzmann transport equation (BTE) method has been developed and successfully applied to many materials, [13][14][15][16][17][18] which makes it possible to study the lattice thermal transport from the perspective of individual phonon modes. In this paper, using the first-principles combining with BTE, we calculated the values of l of two representative pyrochlores, La 2 Sn 2 O 7 and Gd 2 Sn 2 O 7 , with stable lattice structures and increasing masses of the lanthanide elements.…”