  A fundamental understanding of the phonon transport mechanism is important
for optimizing the efficiency of thermoelectric devices. In this study, we
investigate the thermal transport properties of the oxidized form of
phosphorene called phosphorene oxide (PO) by solving phonon Boltzmann transport
equation based on first-principles density functional theory. We reveal that PO
exhibits a much lower thermal conductivity (2.42-7.08 W/mK, at 300 K) than its
pristine counterpart as well as other two-dimensional materials. To comprehend
the physical origin of such low thermal conductivity, we scrutinize the
contribution of each phonon branch to the thermal conductivity by evaluating
various mode-dependent quantities including Gruneisen parameters, anharmonic
threep-honon scattering rate, phase space of three-phonon scattering processes.
Our results show that its exible puckered structure of PO leads to smaller
sound velocities; its broken-mirror symmetry allows more ZA phonon scattering;
and the relatively-free vibration of dangling oxygen atoms in PO gives rise to
additional scattering resulting in further reduction in the phonon lifetime.
These results can be verified by the fact that PO has larger phase space for
three-phonon processes than phosphorene. Furthermore we show that the thermal
conductivity of PO can be optimized by controlling its size or its phonon mean
free path, indicating that PO can be a promising candidate for low-dimensional
thermoelectric devices.
