Optimising thermoelectric transport in n-type Bi_1.8Sb_0.2Te₃ 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mo>̅</mml:mo> </mml:mover> </mml:math> 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.