Abstract
The stability of GeTe in rhombohedral (), face centred cubic (), and simple cubic () phases has been studied using density functional perturbation theory. The rhombohedral phase of GeTe is dynamically stable at 0 GPa, while and phases are stable at 3.1 and 33 GPa, respectively. The pressure-dependent phonon modes are observed in and phases at Γ and points, respectively. The electronic and the thermoelectric properties have been investigated for the stable phases of GeTe. The electronic band gap for rhombohedral and phases of GeTe has been observed as 0.66 and 0.17 eV, respectively, while the phase shows metallic behavior. We have used the Boltzmann transport equation under a rigid band approximation and constant relaxation time approximation as implemented in boltztrap code for the calculation of thermoelectric properties of GeTe. The metallic behavior of phase gives a very low value of Seebeck coefficient compared to the other two phases as a function of temperature and the chemical potential μ. It is observed that the rhombohedral phase of GeTe exhibits higher thermoelectric performance. Due to the metallic nature of phase, negligible thermoelectric performance is observed compared to and -GeTe. The calculated lattice thermal conductivities are low for -GeTe and high for -GeTe. At the relatively higher temperature of 1350 K, the figure of merit is found to be 0.7 for rhombohedral GeTe. The elastic constants satisfy the Born stability criteria for all three phases. The rhombohedral and phases exhibits brittleness and the phase shows ductile nature.
1 More- Received 24 December 2017
- Revised 1 March 2018
DOI:https://doi.org/10.1103/PhysRevB.97.134105
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