Ultra‐Fast One‐Step Fabrication of Cu2Se Thermoelectric Legs With Ni–Al Electrodes by Plasma‐Activated Reactive Sintering Technique

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133615/1/adem201500548-sup-0001-SupFigs-S1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133615/2/adem201500548.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133615/3/adem201500548_am.pd

Improved Thermoelectric Performance of (Fe,Co)Sb\u3csub\u3e3\u3c/sub\u3e-Type Skutterudites from First-Principles

Skutterudite materials have been considered as promising thermoelectric candidates due to intrinsically good electrical conductivity and tailorable thermal conductivity. Options for improving thermal-to-electrical conversion efficiency include identifying novel materials, adding filler atoms, and substitutional dopants. Incorporating filler or substitutional dopant atoms in the skutterudite compounds can enhance phonon scattering, resulting in reduction of thermal conductivity, as well as improving electrical conductivity. The structures, electronic properties, and thermal properties of double-filled Ca0.5Ce0.5Fe4Sb12 and Co4Sb12-2xTexGex compounds (x = 0, 0.5, 1, 2, 3, and 6) have been studied using density functional theory-based calculations. Both Ca/Ce filler atoms in FeSb3 and Te/Ge substitution in CoSb3 cause a decrease in lattice constant for the compounds. As Te/Ge substitution concentration increase, lattice constant decreases and structural distortion of pnictogen rings in the compounds occurs. This indicates a break in cubic symmetry of the structure. The presence of fillers and substitutions cause an increase in electrical conductivity and a gradual decrease in electronic band gap. A transition from direct to indirect band-gap semiconducting behavior is found at x=3. Phonon density of states for both compounds indicate phonon band broadening by the incorporation of fillers and substitutional atoms. Both systems are also assumed to have acoustic-mode-dominated lattice thermal conductivity. For the Co4Sb12-xTexGex compounds, x=3 has the lowest phonon dispersion gradient and lattice thermal conductivity, agreeing well with experimental measurements. Our results exhibit the improvement of thermoelectric properties of skutterudite compounds through fillers and substitutional doping

The Role of Zn in Chalcopyrite CuFeS2: Enhanced Thermoelectric Properties of Cu1–xZnxFeS2 with In Situ Nanoprecipitates

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136267/1/aenm201601299_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136267/2/aenm201601299.pd

Multi‐Scale Microstructural Thermoelectric Materials: Transport Behavior, Non‐Equilibrium Preparation, and Applications

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137226/1/adma201602013_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137226/2/adma201602013.pd

Weak Electron Phonon Coupling and Deep Level Impurity for High Thermoelectric Performance Pb1â xGaxTe

High ZT of 1.34 at 766 K and a record high average ZT above 1 in the temperature range of 300â 864 K are attained in nâ type PbTe by engineering the temperatureâ dependent carrier concentration and weakening electronâ phonon coupling upon Ga doping. The experimental studies and first principles band structure calculations show that doping with Ga introduces a shallow level impurity contributing extrinsic carriers and imparts a deeper impurity level that ionizes at higher temperatures. This adjusts the carrier concentration closer to the temperatureâ dependent optimum and thus maximizes the power factor in a wide temperature range. The maximum power factor of 35 µW cmâ 1 Kâ 2 is achieved for the Pb0.98Ga0.02Te compound, and is maintained over 20 µWcmâ 1 Kâ 2 from 300 to 767 K. Band structure calculations and Xâ ray photoelectron spectroscopy corroborate the amphoteric role of Ga in PbTe as the origin of shallow and deep levels. Additionally, Ga doping weakens the electronâ phonon coupling, leading to high carrier mobilities in excess of 1200 cm2 Vâ 1 sâ 1. Enhanced point defect phonon scattering yields a reduced lattice thermal conductivity. This work provides a new avenue, beyond the conventional shallow level doping, for further improving the average ZT in thermoelectric materials.Ga doping in PbTe not only induces a shallow level impurity but also imparts a deeper impurity level that ionizes at higher temperatures, facilitating the engineering of the temperatureâ dependent carrier concentration, maximizing the power factor over a wider temperature range. This work provides a new avenue, beyond the conventional shallow level doping, for further improving the average ZT in thermoelectric materials.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145409/1/aenm201800659.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145409/2/aenm201800659_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145409/3/aenm201800659-sup-0001-S1.pd

Blocking Ion Migration Stabilizes the High Thermoelectric Performance in Cu2Se Composites

The applications of mixed ionic–electronic conductors are limited due to phase instability under a high direct current and large temperature difference. Here, it is shown that Cu2Se is stabilized through regulating the behaviors of Cu+ ions and electrons in a Schottky heterojunction between the Cu2Se host matrix and in‐situ‐formed BiCuSeO nanoparticles. The accumulation of Cu+ ions via an ionic capacitive effect at the Schottky junction under the direct current modifies the space‐charge distribution in the electric double layer, which blocks the long‐range migration of Cu+ and produces a drastic reduction of Cu+ ion migration by nearly two orders of magnitude. Moreover, this heterojunction impedes electrons transferring from BiCuSeO to Cu2Se, obstructing the reduction reaction of Cu+ into Cu metal at the interface and hence stabilizes the β‐Cu2Se phase. Furthermore, incorporation of BiCuSeO in Cu2Se optimizes the carrier concentration and intensifies phonon scattering, contributing to the peak figure of merit ZT value of ≈2.7 at 973 K and high average ZT value of ≈1.5 between 400 and 973 K for the Cu2Se/BiCuSeO composites. This discovery provides a new avenue for stabilizing mixed ionic–electronic conduction thermoelectrics, and gives fresh insights into controlling ion migration in these ionic‐transport‐dominated materials.The space‐charge region between Cu2Se host matrix and in‐situ‐formed BiCuSeO under a direct current causes drastic suppression of the Cu+ ion migration in such composites and obstructs the reduction reaction of Cu+ into Cu metal. This, together with the effective regulation of carrier concentration as well as enhanced interfacial phonon scattering, greatly stabilizes the improved thermoelectric performance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163457/2/adma202003730-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163457/3/adma202003730_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163457/1/adma202003730.pd

Magnetoelectric interaction and transport behaviours in magnetic nanocomposite thermoelectric materials

How to suppress the performance deterioration of thermoelectric materials in the intrinsic excitation region remains a key challenge. The magnetic transition of permanent magnet nanoparticles from ferromagnetism to paramagnetism provides an effective approach to finding the solution to this challenge. Here, we have designed and prepared magnetic nanocomposite thermoelectric materials consisting of BaFe12O19 nanoparticles and Ba0.3In0.3Co4Sb12 matrix. It was found that the electrical transport behaviours of the nanocomposites are controlled by the magnetic transition of BaFe12O19 nanoparticles from ferromagnetism to paramagnetism. BaFe12O19 nanoparticles trap electrons below the Curie temperature (TC) and release the trapped electrons above the TC, playing an ‘electron repository’ role in maintaining high figure of merit ZT. BaFe12O19 nanoparticles produce two types of magnetoelectric effect—electron spiral motion and magnon-drag thermopower—as well as enhancing phonon scattering. Our work demonstrates that the performance deterioration of thermoelectric materials in the intrinsic excitation region can be suppressed through the magnetic transition of permanent magnet nanoparticles