RESUMO
Cu2Se-based thermoelectric materials exhibit high dimensionless figure of merit (zT) values at elevated temperatures (900-1000 K) but relatively lower zT values at intermediate temperatures, approximately 500 K. We synthesized a series of polycrystalline Cu2Se0.96Te0.04-xIx/Cu2O composites (where x = 0.00, 0.01, 0.02, and 0.03) using an energy-efficient synthesis method conducted at room temperature, followed by heat treatment at 923 K for 6 h. X-ray diffraction (XRD) analysis confirmed the monoclinic crystal structure of the α phase. The introduction of iodine doping at Te sites introduced electron carriers to p-type Cu2Se0.96Te0.04, reducing the hole carrier concentration. Consequently, the electrical resistivity increased, and the thermopower exhibited a significant increase. The incorporation of electron carriers into the p-type Cu2Se0.96Te0.04/Cu2O composites resulted in an enhanced power factor within the medium-temperature range. Specifically, at 500 K, the Cu2Se0.96Te0.02I0.02/Cu2O (x = 0.02) composites demonstrated the highest power factor among the series of Cu2Se0.96Te0.04-xIx/Cu2O composites, measuring 9.1 µW cm-1 K-2. According to the weighted mobility analysis, it is clear that the x = 0.02 composite possesses the optimal carrier concentration, which accounts for its superior power factor compared to the other composites in the series. Furthermore, the Cu2Se0.96Te0.02I0.02/Cu2O composites and Cu2Se0.96Te0.04/Cu2O composites displayed zT values of 0.49 and 0.33, respectively, at 550 K. Additionally, iodine doping led to an enhancement in the average zT values between 450 and 550 K. Therefore, electron doping in p-type materials presents itself as a viable strategy for shifting the operating temperature of a thermoelectric device from high to medium temperature. We successfully fabricated a thermoelectric generator comprising 6 pairs of p-leg Cu2Se0.96Te0.02I0.02/Cu2O composites and n-leg InSb0.94Bi0.06. This TEG achieved impressive results, including a maximum output voltage, power output, power density, and efficiency of 0.115 V, 10.6 µW, 35.1 µW cm-2, and 1.74% at a temperature difference (ΔT) of 120 K.
RESUMO
Mg3Sb2-based Zintl compounds have garnered recent attention as promising materials for thermoelectric applications due to their low thermal conductivity and high zT values as n-type materials. However, the zT values of p-type materials are lower compared to their n-type counterparts. Through a straightforward process involving cold pressing and evacuating-and-encapsulating sintering, we have successfully synthesized a variety of p-type Mg3-xZnxSb2/Sb composites by adding the ZnSb-4%Sb composite into the Mg3Sb2 host material. Structural analyses have provided insights into the role of the ZnSb-4%Sb composite, demonstrating its significance in Zn doping on the Mg sites and Sb acting as an additive in the composite. The introduction of Zn on the Mg tetrahedral sites enhances the concentration of carriers, while the presence of highly conductive Sb grains facilitates the movement of charge carriers between adjacent Mg3-xZnxSb2 grains, thereby promoting mobility. Consequently, the electrical resistivity of the Mg3-xZnxSb2/Sb composites decreases as the Zn content increases. At 710 K, the Mg1.91Zn1.09Sb2/Sb composite exhibits the lowest resistivity, measuring 5.1 mΩ-cm, which is 46 times lower than that of the Mg3Sb2 host. Furthermore, the zT value of the Mg3-xZnxSb2/Sb composites increases with higher Zn content (x), benefiting from a combination of an improved power factor and reduced thermal conductivity. Significantly, our straightforward fabrication process enables us to achieve a maximum zT value of 0.58 at 710 K for the Mg1.91Zn1.09Sb2/Sb composite. This achievement can primarily be attributed to the 8-fold enhancement in power factor compared to the Mg3Sb2 host.