Shihui Chena,
Hanwen Yanga,
Guang Yanga,
Minghui Chenga,
Zipei Zhanga,
Zhangfeng Wu*b and
Jianping Lin*a
aFujian Provincial Key Laboratory of Functional Materials and Applications, School of Materials School of Materials Science and Engineering, Xiamen University of Technology, Xiamen 361024, China. E-mail: jplin@xmut.edu.cn
bSchool of Environmental Science and Engineering, Xiamen University of Technology, Xiamen 361021, China. E-mail: wuzhangfeng@xmut.edu.cn
First published on 29th July 2025
This study presents a comprehensive investigation of the multifunctional properties of ZnSb semiconductors through integrated multiscale simulations. A highly accurate interatomic potential function for ZnSb was constructed and validated using density functional theory (DFT) and deep potential (DP) methods within the temperature range of 300 K to 800 K. Molecular dynamics (MD) simulations revealed the mechanical behavior of ZnSb along different crystallographic axes. The a-axis exhibited significant plastic deformation with a fracture strain of 32%, while the b-axis and c-axis demonstrated brittle fracture characteristics. As the temperature increased from 300 K to 700 K, both the elastic modulus and ultimate strength decreased significantly, indicating the detrimental effect of high temperatures on its mechanical properties. Simulations of thermoelectric performance showed that optimizing carrier concentration can significantly improve the power factor (PF). Electronic thermal conductivity (κe) increases with carrier concentration and temperature, but the Seebeck coefficient performs better at lower carrier concentrations. Thermal transport analysis revealed that the lattice thermal conductivity of ZnSb initially decreases and then increases with rising temperature, with the contribution of Sb–Sb bonds to thermal conductivity exceeding 50%. This study provides a theoretical foundation for the application of ZnSb materials in thermoelectric conversion and high-temperature devices, and highlights the key parameters for performance optimization.
The mechanical properties and thermal stability of ZnSb are crucial for its application in devices. Specifically, the mechanical properties of ZnSb vary significantly due to the anisotropy of its crystal structure.15,16 Guan et al.17 found that the Young's modulus of unstrained ZnSb along the zigzag direction is much higher than that along the armchair direction, indicating strong mechanical anisotropy. The electrical transport properties of ZnSb have also attracted considerable attention.18–20 Ostovari et al.21 found that the electrical conductivity of ZnSb increases with temperature, while the Seebeck coefficient decreases with increasing carrier concentration. Karthikeyan et al.22 used first-principles (FP) calculations to investigate the effect of carrier concentration on the thermoelectric properties of ZnSb and suggested that optimizing the carrier concentration could significantly improve the power factor (PF). The low thermal conductivity of ZnSb is advantageous for improving its thermoelectric performance. Alloying, nanostructuring, and defect engineering are key areas of current research for synergistically modulating thermal conductivity.23–25 Theja et al.26 introduced a second-phase material, γ-Al2O3, via nanocomposite technology to enhance the thermoelectric performance of ZnSb. Furthermore, Fu et al.27 prepared titanium-doped ZnSb nanocomposite thin films and improved the 10-year data retention capability of ZnSb from 103 °C to 120 °C. Studies have demonstrated that the microstructure of ZnSb has a significant impact on its thermal transport properties.28 Jia et al.29 showed that the polycrystalline structure and grain size of ZnSb significantly affect its thermoelectric performance. However, future research needs to integrate in situ characterization with multi-scale simulations.30–32 This approach will clarify two critical aspects: the electron–phonon coupling mechanism under high-temperature conditions and the influence of microscopic defects on thermal transport dynamics.33 This study employs multiscale simulation methods to systematically investigate the mechanical, electrical transport, and thermal properties of ZnSb semiconductors and their temperature dependence. First, based on DFT-optimized lattice parameters and combined with deep potential (DP), a high-precision interatomic potential function is generated, and molecular dynamics (MD) simulations are used to reveal the tensile fracture behavior of the material along different crystallographic axes. Second, Boltzmann transport theory is used to analyze the effect of carrier concentration on the Seebeck coefficient and PF. Finally, thermal conductivity is calculated using the Green–Kubo method, and the contributions of Sb and Zn atomic group to heat transport are analyzed. The research results not only provide a theoretical basis for the application of ZnSb in thermoelectric devices but also offer new insights for material design under multi-physics field coupling.
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Fig. 1 (a) Unit cell of ZnSb; uniaxial tensile models of ZnSb (b) along the a-axis; (c) along the b-axis; (d) along the c-axis. |
After obtaining the ZnSb potential function, we constructed three bulk models [as shown in Fig. 1(b)–(d)] for MD simulations. These models were built by periodically stacking the optimized ZnSb unit cell along the a, b, and c directions. To simulate the infinite crystal behavior of the actual material and avoid boundary effects, we applied periodic boundary conditions (PBCs) in the a, b, and c directions. To study the mechanical properties of the material in different directions, we constructed uniaxial tensile models along the a-, b-, and c-axes, respectively. In the tensile simulations along each direction, tensile stress was gradually applied by controlling the strain in the corresponding axial direction. The PBCs were maintained in the other directions to study the stress–strain behavior of ZnSb.
We also combined Boltzmann transport theory with FP calculations to systematically simulate the thermoelectric properties of ZnSb materials. First, we obtained the electronic structure through DFT calculations. Then, based on these results, we applied the Boltzmann transport equation to calculate the electrical conductivity, carrier concentrations, and thermoelectric properties of the material at different temperatures. Finally, we calculated the HCACF through MD simulations and obtained the thermal conductivity of ZnSb at different temperatures by integrating the HCACF over time and combining it with the Green–Kubo method.
Fig. 3(a)–(c) show the deformation and fracture of ZnSb under tensile strain along the a-, b-, and c-axes. Under a-axis tension, the lattice maintains order up to 25% strain, fracturing at 32%. In contrast, b- and c-axes tensions induce lattice defects at 10% strain, leading to fracture at 14% and 12% strain, respectively. Fig. 3(d) compares the stress–strain curves for different crystallographic axes. Along the b- and c-axes, limited elastic deformation precedes rapid brittle fracture. Along the a-axis, prolonged plastic deformation follows elastic deformation before final fracture.
The significant anisotropy in the mechanical behavior of ZnSb is closely related to its orthorhombic crystal structure (Pnma space group). The superior plastic deformation capability observed along the a-axis suggests the presence of relatively weak atomic bonding or easily activated specific slip systems. These systems allow dislocations to continuously slip under higher stress, resulting in a large degree of shear deformation without immediate fracture. In contrast, the b-axis exhibits high elastic modulus and brittle fracture characteristics. This indicates the likely presence of a strong covalent bond network along this direction. This network hinders dislocation nucleation and movement, leading to rapid cleavage fracture when the material reaches its theoretical strength limit. The brittle behavior along the c-axis is likely a result of its bonding strength and slip characteristics being intermediate between those of the a- and b-axes.
Fig. 4(a) shows the temperature-dependent lattice parameters of ZnSb. As temperature increases from 300 K to 700 K, parameters a, b, and c expand approximately linearly, indicating that the crystal structure expands with increasing temperature. The simulation results (black squares) align closely with those of A. Fisher (red circles). The increase in parameter a is the most significant, while that of c is the smallest, reflecting structural anisotropy. Fig. 4(b) shows the temperature dependence of elastic moduli. The moduli in all three directions decrease with increasing temperature, indicating material softening at elevated temperatures. The elastic modulus in the b-axis direction is the highest, exhibiting strong rigidity, whereas that in the a-axis direction is the lowest, suggesting easier deformation. Fig. 4(c) shows the temperature-dependent ultimate strength. The strength decreases in all three directions with increasing temperature. The b-axis exhibits the highest ultimate strength, whereas the a-axis shows the lowest, highlighting superior load-bearing capacity along the b-axis direction. Fig. 4(d) shows the trend of fracture strain with temperature. While the temperature increase induces only marginal variations in fracture strain overall, the a-axis orientation exhibits the highest fracture strain values, demonstrating superior ductility. In contrast, the c-axis direction shows the lowest fracture strain measurements, characteristic of more brittle fracture behavior. Overall, the degradation of mechanical properties (e.g., strength and stiffness) with temperature implies inherent limitations for ZnSb in high-temperature applications, necessitating targeted performance optimization.
The decrease in elastic modulus and ultimate tensile strength with increasing temperature is a result of intensified lattice thermal vibrations. As temperature rises, the kinetic energy of atoms increases, leading to a larger average interatomic spacing. This increase in interatomic spacing directly weakens the bonding strength between atoms. Microscopically, the elastic modulus reflects the curvature of the interatomic force curve near the equilibrium position. Weakened bonding inevitably leads to a decrease in the elastic modulus. The decrease in ultimate tensile strength reduces the material's ability to resist permanent deformation and fracture. This decline stems from both the weakening of bond strength and thermally activated processes that promote dislocation nucleation and slip. Notably, lattice expansion is most significant along the a-axis. This further confirms that bonding in this direction is most sensitive to temperature changes.
Fig. 5(a) shows the variation of electrical conductivity with carrier concentration. Electrical conductivity rises sharply with increasing carrier concentration, particularly at high concentrations (>1021 cm−3), where the enhancement becomes pronounced, reflecting superior electrical conductivity in ZnSb under such conditions. While the temperature effect on conductivity is modest, a slight increase is still observed at elevated temperatures. Electrical conductivity is proportional to both carrier concentration and mobility (μ). As temperature increases, phonon scattering intensifies, leading to a decrease in carrier mobility. The decrease in mobility and the increase in carrier concentration have counteracting effects. This is why the effect of temperature increase on conductivity is relatively small. Fig. 5(b) illustrates the carrier-concentration dependence of κe. Similar to electrical conductivity, κe increases with carrier concentration, especially at high temperatures (e.g., 700 K), where electronic contributions dominate heat transport. This trend highlights the growing role of electrons in thermal conduction at elevated temperatures. This phenomenon is consistent with the Wiedemann–Franz law. This law states that the electronic contribution to thermal conductivity is proportional to electrical conductivity and temperature. Therefore, the increase in κe/τ is a result of the combined effect of the increase in σ/τ and the rise in temperature. Fig. 5(c) shows the trend of the Seebeck coefficient with carrier concentration. At low carrier concentrations, the Seebeck coefficient remains high but drops rapidly with increasing carrier concentration. This is because high carrier concentrations reduce the thermoelectric potential difference of the material, leading to a decrease in the Seebeck coefficient. Notably, the Seebeck coefficient retains higher values at lower temperatures (e.g., 300 K), suggesting ZnSb's enhanced thermoelectric potential under low temperature and low carrier concentration conditions. Fig. 5(d) shows the variation of the PF with carrier concentration. The power factor exhibits three peaks as the carrier concentration increases. The maximum peak occurs at a carrier concentration of about 1021 cm−3. Increasing temperature significantly increased the peak of the PF, especially at the highest value at 700 K, indicative of improved thermoelectric conversion efficiency at high temperatures. These results demonstrate that the thermoelectric performance of ZnSb can be effectively optimized by adjusting the carrier concentration. Strategic adjustment of carrier concentration under varying temperature conditions is critical for maximizing the material's thermoelectric efficiency.
Fig. 6(a) shows the HCACF of a ZnSb single crystal bulk as a function of time at 300 K. The HCACF decays rapidly with time and tends to zero, indicating that the system reaches thermal equilibrium quickly. Fig. 6(b) shows the variation of thermal conductivity with time at 300 K. It indicates that the calculated thermal conductivity is reliable within this time range. By smoothing the curve, the final calculated thermal conductivity stabilizes at approximately 1.6 W m−1 K−1. Fig. 6(c) shows the trend of lattice thermal conductivity of ZnSb with temperature. The lattice thermal conductivity of ZnSb gradually decreases from about 1.6 W m−1 K−1 at 300 K to about 0.8 W m−1 K−1 at 500 K, which is related to the enhanced lattice vibration and intensified phonon scattering with increasing temperature. Subsequently, the lattice thermal conductivity increases to about 1.0 W (m K)−1 at 700 K, which is attributed to the increase in carrier concentration caused by intrinsic excitation. The simulated lattice thermal conductivity closely matches the experimentally measured value for ZnSb. The numerical deviation from room temperature to 500 K is less than 12.5%, and the simulation and experimental results show a minor difference above 650 K. This minor discrepancy could potentially be attributable to a combination of material-related factors (e.g., impurity content or defect density) and experimental uncertainties in the original data acquisition. Fig. 6(d) shows the contribution of different atomic groups to the total lattice thermal conductivity of ZnSb. The results show that Sb–Sb bond contribute the most to the thermal conductivity, accounting for 50–60%, indicating that it plays a dominant role in heat conduction. In contrast, the contribution of Zn–Zn bond is smaller, around 20–30%, while the Zn–Sb interaction contributes the remaining 10–20%. As the temperature increases, the contribution ratio of each atomic group remain relatively stable, indicating that the heat conduction mechanism of ZnSb does not change significantly with temperature.
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