Anomalous pressure dependence of thermal conductivities of large mass ratio compounds

The lattice thermal conductivities (\ensuremath{\kappa}) of binary compound materials are examined as a function of hydrostatic pressure $P$ using a first-principles approach. Compounds with relatively small mass ratios, such as MgO, show an increase in \ensuremath{\kappa} with $P$, consistent with measurements. Conversely, compounds with large mass ratios that create significant frequency gaps between acoustic and optic phonons (e.g., BSb, BAs, BeTe, BeSe) exhibit decreasing \ensuremath{\kappa} with increasing $P$, a behavior that cannot be understood using simple theories of \ensuremath{\kappa}. This anomalous $P$ dependence of \ensuremath{\kappa} arises from the fundamentally different nature of the intrinsic scattering processes for heat-carrying acoustic phonons in large mass ratio compounds compared to those with small mass ratios. This work demonstrates the power of first-principles methods for thermal properties and advances a broad paradigm for understanding thermal transport in nonmetals.