High Thermoelectric Performance of Nanostructured Mg3Sb2 on Synergistic Te-doping and Mg/Y Interstitial

The nanostructured Mg3Sb2 and Mg3.17Y0.03Sb1.985Te0.015 bulks were prepared using the induction melting-melt spinning (MS)-spark plasma sintering (SPS) method. The grain size of the sample prepared by this method was 50–80 nm. Mg3Sb2 materials co-doped with Y and Te effectively improved the carrier concentration and mobility. The room temperature carrier concentration was significantly increased from 1.28 × 1018 cm−3 for Mg3Sb2 to 7.12 × 1019 cm−3 for Mg3.17Y0.03Sb1.985Te0.015, and carrier mobility from 21.80 cm2V−1 s−1 for Mg3Sb2 to 67.53 cm2V−1 s−1 for Mg3.17Y0.03Sb1.985Te0.015. More carriers were introduced by the doping of the Mg site with the Y element. When Te replaced Sb in the covalent bonding layer, it weakened the polar covalent bond with Mg, thus favoring the movement of carriers. Meanwhile, the co-doping of Y and Te enhanced phonon scattering and reduced the thermal conductivity. The thermal conductivity of the nanostructured Mg3.17Y0.03Sb1.985Te0.015 is about 0.74 Wm−1 K−1, which was only 69% of the bulk counterparts. When the grain size reached the nanometer scale, the grain boundary density increased substantially. The periodic potential field within a single grain was destroyed at the grain boundary. The interface interfered with the carriers and phonon transport, which further reduced the thermal conductivity. At 773 K, the ZT peak value of the nanostructured Mg3.17Y0.03Sb1.985Te0.015 was improved to 1.28, which was significantly higher than that of the non-doped samples.