Strain- and chirality-engineered tunability of electronic and thermoelectric properties in SiC nanotubes: insights from first-principles calculations

Abstract

Silicon carbide nanotubes (SiCNTs) have recently emerged as promising candidates for next-generation thermoelectric applications, owing to their moderate bandgaps and intrinsically lower lattice thermal conductivity—attributable to strong quantum confinement effects. In realistic situations, uniaxial strain arising from lattice mismatch, thermal gradients, or dynamic motion in wearables can significantly modulate the electronic and thermoelectric performance of these nanostructures. In this work, we systematically investigate the strain-dependent electronic and thermoelectric properties of four representative single-walled SiCNTs—three zigzag [(6,0), (10,0), and (11,0)] and one armchair [(6,6)]—using first-principles calculations coupled with Boltzmann transport theory. The results reveal distinct chirality-dependent responses to both compressive and tensile strains. The (6,6) armchair SiCNT exhibits an indirect bandgap of 2.63 eV, while all zigzag SiCNTs show direct bandgaps under strain, with (6,0) showing the narrowest gap (0.49 eV). The Seebeck coefficient remains stable (∼1550 µV K⁻¹) for the (6,6), (10,0), and (11,0) tubes across strain regimes, suggesting robustness suitable for strain-insensitive thermoelectric devices. Conversely, the (6,0) tube displays a broad Seebeck tunability (821–1550 µV K⁻¹), offering potential for adaptive or strain-sensing applications. Strain engineering substantially enhances the thermoelectric power factor (PF/τ), achieving values of 1.36 × 10¹⁴ mW m⁻¹ K⁻² s⁻¹ and 2.07 × 10¹⁴ mW m⁻¹ K⁻² s⁻¹ for (10,0) and (11,0) tubes, respectively, at −2% and −10% strain, and 1.33 × 10¹⁴ mW m⁻¹ K⁻² s⁻¹ for the (6,0) tube under maximum compressive strain. The (6,6) tube shows a ∼1.17 × PF/τ enhancement under compressive loading. Strain modulates normalized electrical conductivity, increasing from ∼1.29 × 10¹⁹ (Ω ms)⁻¹ to 2.25 × 10¹⁹ (Ω ms)⁻¹ in the (6,6) tube under −10% strain, while tensile strain reduces conductivity in (6,0), (10,0) and (11,0) tubes. Normalized electronic thermal conductivity also exhibits chirality-dependent strain sensitivity, ranging from 9.20 × 10¹³ W m⁻¹ K⁻¹ s⁻¹ in (6,0) to >14.69 × 10¹³ W m⁻¹ K⁻¹ s⁻¹ in (6,6) under −10% strain. Notably, the thermoelectric figure of merit (ZT) of the pristine (6,0) SiCNT at 300 K attains a value of ∼0.27, highlighting its promising thermoelectric efficiency relative to carbon nanotubes. These findings provide valuable design insights for the development of flexible, high-performance SiCNT-based nanodevices, including strain sensors, energy harvesters, and thermoelectric coolers.