Abstract
Thermal conductivity of La3Cu3X4 (X=P, As, Sb, Bi) compounds are examined using firstprinciples
density functional theory and Boltzmann transport methods. We observe a trend of
increasing lattice thermal conductivity () with increasing atomic mass, challenging our
expectations as lighter mass systems typically have larger sound speeds and weaker intrinsic
scattering. In particular, we find that La3Cu3P4 has the lowest despite having larger sound
speed and the most restricted available phase space for phonon-phonon scattering, an important
criterion for estimating and comparing among like systems. The origin of this unusual
behavior lies in the strength of the individual anharmonic phonon scattering matrix elements,
which are much larger in La3Cu3P4 than in the heavier La3Cu3Bi4 system. Our finding provides
insights into the interplay of harmonic and anharmonic properties of complex, low thermal
conductivity compounds, of potential use for thermoelectric and thermal barrier coating
applications.
