Energetics and diffusion of gold in bismuth telluride-based thermoelectric compounds

Abstract

We have coupled electron microscopy and energy dispersive spectroscopy experiments with ab-initio modeling to study the solubility and diffusion of Au in Bi 2 Te 3 . We found that thermal annealing of Au films results in Au concentrations in Bi 2 Te 3 above the previously reported solubility limit. The time scale of Au diffusion into Bi 2 Te 3 is also much greater than expected. To explain our observations, we calculate defect formation energies and diffusion barriers within DFT. We identify an interstitial mechanism consistent with the previously observed low solubility and (rapid) anisotropic diffusion. However, the lower formation energies of substitutional defects suggest that they may be active in our experiments and explain the high observed concentrations.1 arXiv:1305.0528v2 [cond-mat.mtrl-sci] 21 Jul 2013 with the Keys and Dutton report of low Au solubility. To explain the result we use density functional theory (DFT) to compute the formation energies of isolated Au defects and their diffusivities. We find interstitial site formation energies and diffusivities are consistent with Keys and Dutton measurements. However, our calculations also suggest a second slower stage of diffusion, associated with lower energy Au substitution in the Bi 2 Te 3 lattice, that occurs after the initial rapid diffusion, accounting for our experimental results. This result suggests the solubilities of metals in highly doped, polycrystalline, or vacancyrich Bi 2 Te 3 may be significantly higher than measured in pristine single-crystal specimens

Codoping ofSb2Te3thin films with V and Cr

“…In fact, from earlier work on electric contacts in the context of thermoelectric applications [27], it has been known that metals in contact with these materials deteriorate. Diffusion and reaction of the metals occur already at moderate temperatures, and in some cases even down to room temperature [28]. The resulting inhomogeneities will affect the structural and magnetic properties [26,29], and will result in inconsistencies in the reported literature in terms of carrier concentrations, magnetic transition temperatures, saturation magnetizations, and magnetic anisotropies.…”

Magnetic order in 3D topological insulators—Wishful thinking or gateway to emergent quantum effects?

“…This is certainly no surprise and a long-standing problem 87 in the thermoelectrics community where the electric contacting with the obvious choices of low electrical resistivity and high thermal conductivity metals has been challenging (with a few exceptions such as Ta 90 ) mostly resulting in the degeneration (or even complete dissolution 91 ) of the electrodes in the case of, e.g., Sn, 92 Ag, 93 and Au. 91 For instance, Cu is notorious for its high diffusivity in Bi 2 Te 3 of 10 À6 cm 2 s À1 parallel to the plane and 3 Â 10 À15 cm 2 s À1 along the c-axis at room temperature 87 and the formation of binary chalcogenides. For electrodes, specific diffusion barriers have been developed (e.g., Ni barriers for Sn electrodes); however, some of them rely on the formation of secondary chalcogen compounds at the interface 92 and so do not provide a solution for achieving controlled, substitutional doping of TIs.…”

“…1(g), as the solubility limit for interstitial metal incorporation is usually low. This is certainly no surprise and a long-standing problem 87 in the thermoelectrics community where the electric contacting with the obvious choices of low electrical resistivity and high thermal conductivity metals has been challenging (with a few exceptions such as Ta 90 ), mostly resulting in the degeneration (or even complete dissolution 91 ) of the electrodes in case of, e.g., Sn, 92 Ag, 93 and Au. 91 For instance, Cu is notorious for its high diffusivity in Bi 2 Te 3 of 10 −6 cm 2 s −1 parallel to the plane and 3•10 −15 cm 2 s −1 along the c-axis at room temperature, 87 and the formation of binary chalcogenides.…”

Highly Effective GeNi Alloy Contact Diffusion Barrier for BiSbTe Long-Term Thermal Exposure

“…13,14 This limitation is also observed for other common metal contacts such as Ag and Cu. In addition, these metals diffuse along the direction of the van der Waals gaps 15−18 limiting high temperature or thermal contact annealing applications. 19−25…”