  In this work, we report thermal conductivity(k) of magnesium telluride (MgTe)
with various crystallographic phases such as rocksalt, zincblende, wurtzite and
nickel arsenic (NiAs) using density functional theory and Boltzmann transport
equation. Our first principles calculations results show the low thermal
conductivity of MgTe with kNiAs < krocksalt < kwurtzite < kzincblende. We
systematically investigated the phonon group velocity, phonon scattering rate
and mode contributed thermal conductivity of transverse acoustic (TA),
longitudinal acoustic (LA) and optical phonons. Our first principles
calculations shows that ultra-low thermal conductivity of 2.645 Wm-1K-1 for
NiAs phase is due to the dominant scattering of TA and LA phonons by low
frequency optical phonons. We also analyzed the length dependence thermal
conductivity of MgTe at nanometer length-scales. At nanometer length scales
such as 50 nm for NiAs phase, room temperature thermal conductivity of less
than 1.4 Wm-1K-1 shows a promising nature of MgTe for thermoelectric
applications.
