The discovery of new thermoelectric materials has the potential to benefit from advances in high-throughput methodologies. Traditional synthesis and characterization routes for thermoelectrics are time-consuming serial processes. In contrast, high-throughput materials discovery is commonly done by thin film growth, which may produce microstructures that are metastable or compositionally graded and, therefore, are challenging to characterize. As a middle ground between bulk synthesis and thin film deposition, we find that the aerosol deposition process can rapidly produce samples that exhibit electronic property trends consistent with those produced by traditional bulk means. We demonstrate rapid growth of discrete thermoelectric thick films of varying chemical compositions (Pb1-xSnxTe) from PbTe and SnTe polydisperse micrometer sized powder feedstocks. The high deposition rate (near 1 μm min-1) and resultant microstructures are advantageous as the diffusion length scales promote rapid thermal treatment and equilibrium phase formation. Room-temperature high-throughput measurements of the Seebeck coefficient and resistivity are compared to traditionally produced bulk materials. The Seebeck coefficient of the films follows the trends of traditional samples, but the resistivity is found to be more sensitive to microstructural effects. Ultimately, we demonstrate a framework for exploratory materials science using aerosol deposition and high-throughput characterization instrumentation.
Bibliographical noteFunding Information:
Aerosol deposition of mixed thermoelectric powders has shown promise as a method for exploring high dimensional phase spaces. Films were successfully deposited from mixtures of PbTe and SnTe powders. The as-deposited microstructures of the films were found to have discrete crystallites of PbTe and SnTe, but a short thermal treatment enabled homogenization of the microstructure. X-ray diffraction confirmed the merging of two rock-salt (PbTe and SnTe) structures into a single homogeneous phase. Control of the atomic fractions of aerosolized PbTe and SnTe powders resulted in differing film stoichiometry that was confirmed by lattice parameter shifts and EDS measurements. Room-temperature Seebeck measurements of the films showed that the trend of the aerosol-deposited films follows that of the traditional pellet samples. Variation of the Seebeck coefficient is likely a result of local chemical inhomogeneity resulting from the deposition or annealing processes. The trend observed for the Seebeck coefficients suggests that the carrier concentration of the films is indirectly controlled by the intrinsic cation vacancies present in SnTe. Resistivity of the films was found to be an order of magnitude higher than traditional samples. The porosity present in the microstructure of the film likely reduces the mobility, leading to the overall high resistivity. The anticipated increasing resistivity with PbTe content arising from reducing carrier density is observed in the films. As the quality and thickness of the films increases, measurements on film samples are likely to continue to converge toward those of traditionally produced samples. While we have demonstrated successful formation of alloyed materials with AD, the process is by no means optimized. Improved implementation of combinatorial AD will require the convergent studies of aerosol deposition physics, including the influence of particle size distribution, flow conditions, and particle structure on the coating processes, and of post deposition treatment methods to create chemically homogeneous films, with minimal interfacial effects. Automated, optimized AD has the potential to substantially reduce sample production time as a part of high-throughput materials discovery systems. ARPA-E Award DE-AR0000840, ARPA-E Award DE-AR0001094, and NSF award DMR 1555340. The authors declare no competing financial interest.
© 2019 American Chemical Society.
- Seebeck coefficient
- high-throughput methodology
- thermoelectric materials
- thick film