Abstract
In this paper, we systematically investigate the effect of hydrostatic pressure on the phononic and electronic transport properties of orthorhombic p-type GeSe using first-principles based Boltzmann transport equation approach. It is found that the lattice thermal conductivities along the a and c directions increase with pressure, whereas it experiences a decrease along the b direction. This anomalous pressure dependent lattice thermal conductivity is attributed to the combined effect of enhanced phonon group velocity and reduced phonon lifetime. Additionally, the optical phonon branches have remarkable contributions to the total lattice thermal conductivity. The electronic transport calculations indicate that the Seebeck coefficient undergoes a sign change from p-type to n-type along the a direction under pressure, and a dramatic enhancement of the power factor is observed due to the boost of electrical conductivity. The predicted ZT values along the a, b, and c directions are 1.54, 1.09, and 1.01 at 700 K and 8 GPa, respectively, which are about 14, 7.3, and 1.9 times higher than those at zero pressure at experimental carrier concentration of ~1018 cm−3. Our study is expected to provide a guide for further optimization of the thermal and charge transport properties through hydrostatic pressure.
Highlights
Thermoelectric materials, enabling a direct and reversible conversion between thermal energy and electricity based on the Seebeck effect and Peltier effect, play a vital role in the development of sustainable energy technologies
The change of lattice constants with compression is consistent with previous x-ray-diffraction measurements[27], which indicates that the length along the a-axis direction is more compressible than along the b www.nature.com/scientificreports and c directions
Considering the phase-transition temperature and pressure above, in this work, we focus on the thermoelectric properties of low-temperature orthorhombic phase GeSe below 8 GPa
Summary
Thermoelectric materials, enabling a direct and reversible conversion between thermal energy and electricity based on the Seebeck effect and Peltier effect, play a vital role in the development of sustainable energy technologies. Since the Seebeck coefficient and electrical conductivity are strongly dependent on the electronic band structures, pressure can be used as a powerful tool to optimize the thermoelectric transport properties through the modification of the electronic band structures. Previous works have reported a remarkable enhancement of thermoelectric properties under high pressure either by pressure-enhanced electrical conductivity or by improved Seebeck coefficient[9,10,11,12,13,14,15,16,17,18,19]. Most previous theoretical works on the pressure dependence of the thermoelectric properties calculated the lattice thermal conductivity based on the Debye-Callaway model[6,25], which ignores the contributions of optical phonon modes, and the effect of pressure on the phonon transport cannot be obtained exactly. The underlying mechanism is explored in detail by the phonon spectrum and electronic band structures analysis
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