Using first-principles calculations and the electron–phonon
Wannier and Boltzmann transport equation, the electronic and lattice
transport properties along with thermoelectric performance of FeOCl-type
compounds ScXI (X = S, Se, Te) are investigated. It is found that
the transport coefficients that determine the thermoelectric properties
are significantly affected by electron–phonon coupling, with
optical phonon scattering contributing importantly to the transport
properties that produce low lattice thermal conductivity at room temperature.
Near the Fermi level, the conductivity and relaxation time of holes
are 1 order of magnitude larger than that of electrons, while both
of them contribute negligibly to the thermal conductivity. The significantly
enhanced power factor of holes along with low lattice thermal conductivity
give rise to remarkable thermoelectric performance, with ZT of p-type ScSI reaching 1.02. More importantly, we find that both
compressive and tensile strain engineering significantly suppress
the lattice thermal conductivity by enhancing the phonon scattering,
while retaining the electronic band structures almost unchanged near
the Fermi level. As a result, a giant thermoelectric figure of merit
is predicted in ScSI with a ZT value as high as 4.56
under isotropic strain ratio (−0.6%), corresponding with a
hydrostatic pressure of 1.08 GPa. The present work not only uncovers
a new family of high-performance thermoelectric materials but also
casts physical insights on optimizing the figure of merits for potential
applications.