Microstructures And Thermoelectric Properties Of Zn₄Sb₃ Prepared By Melt-spinning Method

Zn₄Sb₃ is one of the promising thermoelectric materials for its much lower thermal conductivity in the moderate temperature range. While the fragility and the microcrack which result from the phase transition greatly decrease the mechanical property and processability. The research of new preparation method and treatment for bulk Zn₄Sb₃ which has good thermoelectric performance, high mechanical property and well processability has attracted substantial interest.In this thesis, compact and crack-free bulk Zn₄Sb₃ samples with nanostructure have been prapared by combining melt-spinning with spark plasma sintering (MS-SPS). In order to investigate the relationship between microstructure and thermoelectric performance of bulk materials, the phase and microstructure of melt-spinning ribbons, annealing ribbons and bulk materials are studyed by XRD and Field Emitted Scanning Electron Microscopy(FESEM), and the thermoelectric properties of bulk materials are measured. and the main obtained results as follows.Multi-phase ribbons are produced from Single phase Zn₄Sb₃ by melt-spinning method. Zn₄Sb₃ is the principle phase of the ribbons, ZnSb, Zn, Zn₃Sb₂ are the second phases; the multi-phase ribbons of melt spinning can change into single phase Zn₄Sb₃ when annealing at 200℃for 30 minute; the compact bulk materials are obtained after SPS at 400℃for 5 minute using the melt-spinning ribbons.Owning to the variance of the cooling rate,the morphology of free and contact surface of ribbons obtained by melt-spinning are significantly different: in the free surface, rodlike crystals with micrometer scale and the Zn-rich alloy particles distributed between the rodlike crystal boundaries are formed; in the contact surface, the nanoparticles with 50nm-150nm size are observed by FESEM. With the increase of annealing temperature, the diffusion of Zn-rich alloy particles into rodlike crystals is observed in the free surface; the size of the nanoparticles becomes smaller with increasing temperature in the contact surface, but the aggregation and growth of the nanoparticles can be found over 300℃. The big crystal and nanoparticles interlaced with each other are found in the fractured surface morphology after melt-spinning-SPS. The electrical conductivity and thermal conductivity of MS-SPS samples are lower than that of melt sample, and the Seebeck coefficient of MS-SPS samples is higher than that of melt sample for the Zn_4.32Sb₃ chemical composition; the maximum ZT value riches 0.96 at 700K for 2000rpm, 0.02MPa melt-spinning ribbons after SPS, which is 30 percent higher than the melt samples. The pressive strength is much larger than the melt samples and the melt-SPS samples, the mechanical property of Zn₄Sb₃ have been optimized by melt-spinning-SPS method.