Utilizing Point Defects in Zintl Compounds to Understand and Engineer their Thermoelectric Properties

Wood, Maxwell

doi:https://doi.org/10.21985/n2-d9k7-yp64

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Utilizing Point Defects in Zintl Compounds to Understand and Engineer their Thermoelectric Properties

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A significant portion of material science research is concerned with understanding theway that defects affect the properties materials. In the field of thermoelectrics introducingor removing point (0D), dislocation (1D), grain boundary (2D), or precipitate (3D) defectsare popular methods for altering a materials thermoelectric efficiency. Herein I discussdifferent studies conducted during my PhD that focus on using point defects to alter theelectronic properties of Zintl based compounds.Point defects in a material can bring about changes in a material’s electronic transportthat can be classified as stemming from changes in: carrier concentration/electron chem-ical potential, band structure, or scattering. Herein lies a discussion of what ways eachof these transport parameters are affected by point defects, as well as methods to controlpoint defects that lead to these changes in parameters. This document demonstrates twodifferent methods for controlling carrier concentration via point defects by using secondaryphases (Phase Boundary Mapping in ZnSb) or a vapor phase (Saturation Annealing in 3Mg3Sb2) to set atomic chemical potentials, which in turn affects the materials point defectconcentration. This document also discuss how the aliovalent substitution of Al onto theMg site of Yb14MgSb11can be used to shift the Fermi-level of a material to learn about itsunderlying band structure. The final two chapters of this document focus more on howpoint defects can lead to changes in transport that do not necessarily deal with changesin carrier concentration. This includes how isovalent substituion of Mg onto Zn site ofCaZn2Sb2can be used to alter the band structure of the compound, or how isovalent Ybsubstitution onto the Mg site in Mg3Sb1.5Bi0.5can result in an increase in scattering dueto changes in bonding in the material.

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