Optimizing the thermoelectric performance of (GeTe)_0.962(Bi₂Te₃)_0.038 alloy through anisotropic texturing

Thermoelectric materials have emerged as promising candidates for converting waste heat into electricity, this research investigates the thermoelectric potential of the p-type (GeTe)_0.962(Bi₂Te₃)_0.038 semiconducting alloy. Samples were produced via melt-spinning at 240 and 2400 RPM, followed by hot-pressing, and analyzed for the effects of processing conditions and sample orientation. The Seebeck coefficient (α) remained unaffected by processing speed and orientation, while electrical resistivity (ρ) exhibited anisotropy, increasing in samples oriented perpendicular to the hot-pressing direction due to alignment along the (001) plane with weaker Van der Waals bonds. Conversely, parallel-oriented samples to the (110) plane had lower resistivity due to stronger covalent bonding. Thermal conductivity (κ) exhibited an inverse relationship with electrical resistivity, as predicted by the Wiedemann-Franz law. Electronic thermal conductivity was lower perpendicular to the hot-pressing direction due to the higher electrical resistivity in this direction, while the lattice thermal conductivity decreased markedly with faster cooling at 2400 RPM wheel speed. Microstructural analysis revealed that higher wheel speed resulted in smaller grain sizes and increased grain boundary density, promoting phonon scattering and consequently effectively reducing κ_l. These findings were corroborated by SEM, which demonstrated reduced flake thickness and narrower columnar grain widths at elevated wheel speeds. The thermoelectric figure of merit (ZT) achieved a maximal value of ∼1.4 in fine-grained perpendicular samples produced at 2400 RPM over a wide temperature range of 310–500°C. This exceptional performance is attributed to an optimized balance of carrier concentration and grain boundary effects, which effectively suppressed thermal conductivity while preserving favorable electrical properties.