Modeling critical thermoelectric transports driven by band broadening and phonon softening

Abstract Critical phenomena are one of the most captivating areas of modern physics, whereas the relevant experimental and theoretical studies are still very challenging. Particularly, the underlying mechanism behind the anomalous thermoelectric properties during critical phase transitions remains elusive, i.e., the current theoretical models for critical electrical transports are either qualitative or solely focused on a specific transport parameter. Herein, we develop a quantitative theory to model the electrical transports during critical phase transitions by incorporating both the band broadening effect and carrier-soft TO phonon interactions. It is found that the band-broadening effect contributes an additional term to Seebeck coefficient, while the carrier—soft TO phonon interactions greatly affects both electrical resistivity and Seebeck coefficient. The universality and validity of our model are well confirmed by experimental data. Furthermore, the features of critical phase transitions are effectively tuned. For example, alloying S in Cu2Se can reduce the phase transition temperature but increase the phase transition parameter b. The maximum thermoelectric figure of merit zT is pushed to a high value of 1.3 at the critical point (377 K), which is at least twice as large as those of normal static phases. This work not only provides a clear picture of the critical electrical transports but also presents new guidelines for future studies in this exciting area

Are Cu2Te‐Based Compounds Excellent Thermoelectric Materials?

Most of the state‐of‐the‐art thermoelectric (TE) materials exhibit high crystal symmetry, multiple valleys near the Fermi level, heavy constituent elements with small electronegativity differences, or complex crystal structure. Typically, such general features have been well observed in those well‐known TE materials such as Bi2X3‐, SnX‐, and PbX‐based compounds (X = S, Se, and Te). The performance is usually high in the materials with heavy constituent elements such as Te and Se, but it is low for light constituent elements such as S. However, there is a great abnormality in Cu2X‐based compounds in which Cu2Te has much lower TE figure of merit (zT) than Cu2S and Cu2Se. It is demonstrated that the Cu2Te‐based compounds are also excellent TE materials if Cu deficiency is sufficiently suppressed. By introducing Ag2Te into Cu2Te, the carrier concentration is substantially reduced to significantly improve the zT with a record‐high value of 1.8, 323% improvement over Cu2Te and outperforms any other Cu2Te‐based materials. The single parabolic band model is used to further prove that all Cu2X‐based compounds are excellent TE materials. Such finding makes Cu2X‐based compounds the only type of material composed of three sequent main group elements that all possess very high zT  s above 1.5.By introducing Ag2Te into Cu2Te, the phase‐transition features are well tuned and the high carrier concentration is substantially reduced, leading to a record‐high zT of 1.8. It is demonstrated that Cu2Te, Cu2S, and Cu2Se are all excellent thermoelectric (TE) materials that are beyond all other state‐of‐the‐art TE materials.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152745/1/adma201903480-sup-0001-SupMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152745/2/adma201903480_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152745/3/adma201903480.pd