Boosting thermoelectric performance in Bi2Te3 crystals by Ge/Se co-doping and melt-growth synthesis

This study investigates the structural and thermoelectric properties of intrinsic p-type Bi 2 Te 3 and (Bi 1- x Ge x ) 2 T e2.7 Se 0.3 single crystals, which were synthesized using a modified vertical Bridgman technique. X-ray diffraction analysis confirmed the formation of single-phase Bi 2 Te 3 and validated the optimized substitution of Ge and Se. The doped samples exhibited reduced thermal conductivity compared to the undoped counterpart, primarily due to enhanced phonon scattering mechanisms. Electrical transport measurements revealed that the enhancement in the thermoelectric figure of merit ( ZT ) is driven by reduced thermal conductivity, resulting from increased phonon scattering at grain boundaries and defects. In the sample with x = 0.04, a 2.3-fold reduction in thermal conductivity was observed, which led to approximately a 3-fold enhancement in the power factor (5394 μW/m·K 2 ) and a 3.9-fold increase in ZT value (0.67) compared to the pristine sample at 350 K. Consequently, a fourfold enhancement in the ZT value of ∼0.7 at 350 K was achieved for (Bi 0.94 Ge 0.06 ) 2 Te 2.7 Se 0.3 , due to a 5.6-fold reduction in electrical resistivity compared to Bi 2 Te 3 . These findings highlight the potential of Ge/Se co-doping and melt-growth synthesis in developing advanced thermoelectric materials. • Ge and Se co-doping in Bi2Te3, achieved through a modified vertical Bridgman method, successfully optimized structural and transport properties, resulting in homogeneous, single-phase materials. • The incorporation of Ge and Se significantly suppressed thermal conductivity in Bi2Te3, primarily due to enhanced phonon scattering from lattice imperfections, grain boundaries, and mass fluctuation effects. This reduction is critical for improving thermoelectric performance. • A nearly fourfold increase in the thermoelectric figure of merit (ZT) was observed in a sample with x=0.04 compared to undoped Bi2Te3, attributed to reduced thermal conductivity and a substantial increase in the power factor. This demonstrates the effective optimization of both thermal and electrical transport. • The (Bi0.94Ge0.06)2Te2.7Se0.3 composition achieved the highest ZT value of approximately 0.7 at 350 K, mainly due to a significant decrease in electrical resistivity. This research offers a scalable synthesis method and a viable path for enhancing low-temperature thermoelectric materials.