Microwave Irradiation to Produce High Performance Thermoelectric Material Based on Al Doped ZnO Nanostructures

Abstract

Microwave irradiation is found to be effective to provide highly crystalline nanostructured materials. In this work, this technique has been used to produce highly improved thermoelectric (TE) material based on aluminum (Al) doped zinc oxide (ZnO) nanostructures (NSs). The effect of Al dopant at the concentration range 0.5–3 mol % on the structural and TE properties has been investigated in more details. The optimum concentration of Al for better TE performance is found to be 2 mol %, which could significantly increase the electrical conductivity and reduce the thermal conductivity of ZnO NSs and thus enhance the TE performance. This concentration showed almost metallic conductivity behavior for ZnO NSs at low temperatures, e.g., below 500 K. The electrical conductivity reached 400 S/m at room temperature, which is around 200 times greater than the value recorded for the pure ZnO NSs. Remarkably, the measured room temperature thermal conductivity of the microwave synthesized ZnO NSs was very low, which is around 4 W/m·K. This value was further reduced to 0.5 W/m·K by increasing the Al doping to 3 mol %. The figure of merit recorded 0.028 at 675 K, which is 15 times higher than that of the pure ZnO NSs. The output power of a single leg module made of 2 mol % Al doped ZnO NSs was 3.7 µW at 485 K, which is higher by 8 times than that of the pure sample. These results demonstrated the advantage of the microwave irradiation rout as a superior synthetic technique for producing and doping promising TE nanomaterials like ZnO NSs.

Graphene-Based Composites for Thermoelectric Applications at Room Temperature

“…Zn 0.995 Al 0.005 O displays a large Seebeck coefficient with a negative sign (−590 µV/K), but the electrical resistivity is extremely high (Table 1). It is worth mentioning that Al doping is needed to improve the electrical properties of ZnO [37][38][39]. In this case, the electrical resistivity remains higher in comparison with other thermoelectric oxides (i.e., Ca 3 Co 4 O 9 ).…”

“…As oxides, we chose p-type Ca 3 Co 4 O 9 and n-type Zn 0.995 Al 0.005 O. These oxides were selected due to their ability to modify the electrical and thermal properties through the regulation of the interface and boundary grains [37,38]. In addition, the thermal conductivity of oxides displays size-dependent effects, which allows for the suppression of thermal conductivity through effective phonon scattering [39].…”

Review on grain size effects on thermal conductivity in ZnO thermoelectric materials

“…Table 2 also showed that a smaller grain size, which results in lower thermal conductivity, fits well with the Callaways model, as discussed in the previous section. For instance, Baghdadi et al 's 53 Al-doped ZnO nanoparticles synthesized by microwave irradiation method yielded nanometer-sized ZnO. The obtained ZnO grain size sample was 24.1 nm, where its thermal conductivity measured at 700 K was ∼2.2 W m −1 K −1 and 4 W m −1 K −1 at room temperature.…”

“…Another effective technique used to adjust nanostructure morphology/size of ZnO was using microwave irradiation and has been found by in providing highly efficient TE materials. 53 The reduction in grain size leads to a decrease in thermal conductivity due to phonon scattering at the grain boundaries. 103 A novel thermoelectric AI-doped ZnO ceramics with nanopowders size was proven enhanced TE performance through nano/microstructure engineered using synthesis technique.…”