Thermoelectric enhancement of p-type Si 80Ge 20 alloy via co-compositing of dual oxides: Respective regulation for power factor and thermal conductivity by β-Ga 2O 3 and SiO 2 aerogel powders

Abstract

Si-based thermoelectric (TE) materials are exhibiting remarkable perspectives in self-energized applications with their special advantages. However, the relatively high total thermal conductivity (<i>κ</i>) prevents their TE enhancement. Here, a strategy of co-compositing dual oxides was implemented for enhancing the TE properties of p-type Si₈₀Ge₂₀ bulks. Composited Ga₂O₃ was demonstrated to enhance the power factor (<i>PF</i>) due to the crystallization-induced effect of produced Ga by decomposition on SiGe matrix. Associating with compositing SiO₂ aerogel (a-SiO₂) powder, not only introduced the fine amorphous inclusions and decreased the grain size of host matrix, but also various nano morphologies were formed, i.e., nano inclusions, precipitations, twin boundaries (TBs), and faults. Combining with the eutectic Ge, hierarchical scattering centers impeded the phonon transport comprehensively (decreasing the phonon group velocity (<inline-formula> <math display="inline" id="MA1"><mrow><msub><mi>v</mi><mtext>a</mtext></msub></mrow></math></inline-formula>) and relaxation time) for reducing the lattice-induced thermal conductivity (<inline-formula> <math display="inline" id="MA2"><mrow><msub><mi>κ</mi><mtext>l</mtext></msub><mo stretchy="false">)</mo></mrow></math></inline-formula>. As a result, a minimum <inline-formula> <math display="inline" id="MA3"><mi>κ</mi></math></inline-formula> of 2.38 W·m⁻¹·K⁻¹ was achieved, which is significantly dropped by 32.6% in contrast with that of the pristine counterpart. Ultimately, a maximal dimensionless figure of merit (<i>ZT</i>) of 0.9 was achieved at 600 ℃, which is better than those of most corresponding oxide-composited Si-based bulks.