Optimising thermoelectric transport in n-type Bi1.8Sb0.2Te3 alloys via isovalent Y doping

Abstract

This study explores the thermoelectric properties of isovalent Y-doped Bi _1.8− _x Y _x Sb _0.2 Te _3 at various doping levels ( x = 0.04, 0.08, 0.12) prepared using the solid-state reaction method. X-ray diffraction (XRD) analysis confirmed a rhombohedral structure with the R $\mathop{3}\limits^{\unicode{773}}$ m space group. The SEM micrographs provide evidence of lamellar-textured samples characterized by minimal porosity. The electrical resistivity of compounds demonstrated typical behavior of degenerate semiconductors, showing an increase with rising temperature. Seebeck coefficient and Hall effect measurements identified electron-dominant charge carriers, with the Seebeck coefficient displaying a consistent increase across the temperature range of 30 to 310 K. This behavior implies a uniform density of states and a stable position of Fermi energy within the samples, and it is verified from the computational studies which shows the similar band gap values. The pristine sample achieved the highest power factor ( PF ) of 197 μW mK ^−2 at 310 K. Optimized Y doping significantly reduces the thermal conductivity of Bi _1.8 Sb _0.2 Te _3 due to enhanced phonon scattering caused by point defects. Notably, 40% increase in ZT compared to pristine with the highest value of 0.17 at 310 K, for the x = 0.12 sample.

Keywords

• rare earth doping
• isovalent doping
• thermal conductivity
• thermoelectric
• point defects