Effects of rattling behavior of K and Cd atoms along different
directions in anisotropic KCdAs on lattice thermal transport and
thermoelectric properties
Abstract
We employ advanced first-principles methodology, merging self-consistent
phonon theory and the Boltzmann transport equation, to comprehensively
explore the thermal transport and thermoelectric properties of KCdAs.
Notably, the study accounts for the impact of quartic anharmonicity on
phonon group velocities in the pursuit of lattice thermal conductivity
and investigates 3ph and 4ph scattering processes on phonon lifetimes.
Through various methodologies, including examining atomic vibrational
modes and analyzing 3ph and 4ph scattering processes, the paper unveils
microphysical mechanisms contributing to the low
$\kappa_{L}$ within KCdAs. Key features include
significant anisotropy in Cd atoms, pronounced anharmonicity in K atoms,
and relative vibrations in non-equivalent As atomic layers. Cd atoms,
situated between As layers, exhibit rattling modes and strong lattice
anharmonicity, contributing to the observed low
$\kappa_{L}$. Remarkably flat bands near the valence
band maximum translate into high PF, aligning with ultra-low
$\kappa_{L}$ for exceptional thermoelectric
performance. Under optimal temperature and carrier concentration doping,
outstanding \textit{ZT} values are achieved: 4.25
(a(b)-axis, p-type), 0.90 (c-axis, p-type), 1.78 (a(b)-axis, n-type),
and 2.36 (c-axis, n-type).