The role of metavalent bonding in thermal conductivity anomalies of lanthanum monopnictides

In this study, we theoretically investigate the primary origins of the anomalous behavior in lattice thermal conductivity observed in binary lanthanum monopnictides with a rocksalt structure, specifically LaP and LaBi. We explore the surprising phenomenon where LaBi, despite having a larger average atomic mass, smaller acoustic phonon velocities, and smaller acoustic-optical frequency gap, does not exhibit lower lattice thermal conductivity compared to LaP. Our findings reveal that the nature of bonding plays a significant role in these anomalies, particularly in the case of LaP. We explore how these differences in bonding influence anharmonicity and phonon scattering, which ultimately affect thermal transport.