Investigation on transport properties and anomalously heat-carrying optical phonons in KXY (X = Ca, Mg; Y = Sb, Bi)

In this work, we systematically studied the thermal transport properties of ternary zintl compound KXY using self-consistent phonon theory combined with compressive sensing technology and the Boltzmann transport equation. The effects of quartic anharmonic induced phonon renormalization and 4 - phonon scattering on the results are fully considered. Vibrational mode visualization reveals that the anomalous contribution of optical phonons to lattice thermal conductivity in KCaBi originates from high-speed out-of-phase vibrations of Ca atoms. We analyzed the microscopic mechanism of heat transport from the perspective of atomic bonding combined with the results of group velocity, scattering rate, Gru¨neisen parameter, mean free path, etc. In addition, we verified and predicted the mechanical properties in KXY by calculation.