Composition Modulation of Ag<sub>2</sub>Te Nanowires for Tunable Electrical and Thermal Properties

Yang, Haoran; Bahk, Je‐Hyeong; Day, Tristan; Mohammed, Amr; Min, Bok Ki; Snyder, G. Jeffrey; Shakouri, Ali; Wu, Yue

doi:10.1021/nl502551c

Cited by 82 publications

(100 citation statements)

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“…(unpubilished work) The low power factor in this work can also be attributed to the much lower packing density of our nanofiber sample than other hot pressed nanostructured pellets. 3,5,13 In our samples, charge can mainly transport through 1-D channels along the nanofibers, which will significantly reduce the effective conducting channels thereby the electrical conductivity and power factor. 42 CONCLUSIONS Ultra-long Ag x Te y nanofibers were synthesized by combining electrospinning and the galvanic displacement reaction.…”

Section: Resultsmentioning

confidence: 99%

Thermoelectric Properties of Ultralong Silver Telluride Hollow Nanofibers

et al. 2015

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Ultra-long Ag x Te y nanofibers were synthesized for the first time by galvanically displacing electrospun Ni nanofibers. Control over the nanofiber morphology, composition and crystal structure was obtained by tuning the Ag + concentrations in the electrolytes. While Te-rich branched p-type Ag x Te y nanofibers were synthesized at low Ag + concentrations, Ag-rich nodular Ag x Te y nanofibers were obtained at high Ag + concentrations. The Te-rich nanofibers consist of coexisting Te and Ag 7 Te 4 phases, and the Ag-rich fibers consist of coexisting Ag and Ag 2 Te phases. The energy barrier height at the phase interface is found to be a key factor affecting the thermoelectric power factor of the fibers. A high barrier height increases the Seebeck coefficient, S, but reduces the electrical conductivity, σ, due to the energy filter effect. The Ag 7 Te 4 /Te system was not competitive with Ag 2 Te/Ag system due to its high barrier height where the increase in S could not overcome the severely diminished electrical conductivity. The highest power factor was found in the Ag-rich nanofibers with an energy barrier height of 0.054 eV. INTRODUCTIONThe rising cost of compliance to laws and regulations (from the Clean Air Act to Geologic Sequestration) for consuming non-renewable energy resources is the key driver to improve the efficiency of environmentally-friendly and renewable energy generation. 1 Thermoelectric materials offer simple, silent and reliable solid-state energy conversion devices due to their unique ability to directly convert heat into electricity and viceversa without moving parts or bulk fluids. The efficiency of a thermoelectric device can be determined by the thermoelectric figure-of-merit (ZT), given by ܼܶ = ܵ ଶ ߪܶ/ߢ. Here S, σ, κ, T, and S 2 σ are the Seebeck coefficient, electrical conductivity, thermal conductivity, temperature, and power factor, respectively. Nonetheless, the interrelationships of these key parameters in a bulk material tend to offset one another making it difficult to improve ZT. 2 Recent research in low-dimensional, especially one-dimensional (1-D) thermoelectric nanostructures, has invigorated the field by identifying quantum confinement, the energy filtering effect, and stronger phonon scattering effects to enhance S 2 σ and reduce κ. 3-5 Quantum confinement shifts the Fermi level away from the conduction band, creating a greater energy difference between them thereby improving the power factor. 6 Energy filtering enhances the average carrier energy by filtering out low energy carriers at grain boundaries or interfaces, thus increasing the Seebeck coefficient and optimizing the power factor. 7 Stronger phonon scattering at the grain boundaries and interfaces is anticipated in 1-D nanostructures due to their larger surface-to-volume ratio, which can significantly decrease the thermal conductivity. Among 1-D thermoelectric materials, nanotubes benefit from their unique wall thickness, which provides an extra de-

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Section: Resultsmentioning

confidence: 99%

Thermoelectric Properties of Ultralong Silver Telluride Hollow Nanofibers

et al. 2015

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“…Figure 5(b) shows the thermopower factor, 2 , where and are Seebeck coefficient and electrical conductivity, respectively. When the phase of Ag 2 Te changes into cubic, power factor suddenly decreases up to 25 W/mK 2 , but larger value than other polycrystalline Ag 2 Te results [20,21]. Our Ag 2 Te nanowires with single crystalline nature grown by vapor-solid method result in the benefit to higher electrical conductivity, expecting excellent performance like high for thermoelectric applications.…”

Section: Resultsmentioning

confidence: 88%

Thermoelectric Properties of a Single Crystalline Ag₂Te Nanowire

Lee

Shin

Song

et al. 2017

Journal of Nanomaterials

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Silver chalcogenides have received much attention in potential thermoelectric materials research because of high carrier mobility and low effective mass. Among them, in Ag 2 Te, it was reported that the phase transition from monoclinic to cubic phase occurs at relatively low temperatures, so that extensive research for effective application using this material has been aroused. In this work, we investigated how 1-dimensional nanostructure affects the thermoelectric properties through as-synthesized single crystalline Ag 2 Te nanowires. Adopting well-defined thermoelectric MEMS device structure and transferring an individual Ag 2 Te nanowire, we measure electrical resistance and Seebeck coefficient as a function of temperature. When the phase changes from monoclinic to cubic, the resistance increases, while absolute Seebeck coefficient value decreases. These results are compared with previous reports for Ag 2 Te bulk and film, suggesting the increased density of states of the carriers due to nanowire structure.

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“…1,2 The semiconducting and magnetic properties of Ag 2 Te have been found to possess large magnetoresistance, high carrier mobility and low thermal conductivity. 3,4 In particular, the monoclinic β-Ag 2 Te with low thermal conductivity has been concerned as one of promising thermoelectric materials and also employed to be a second-step host material chemically transformed into a series of metal tellurides. 4,5 In addition, recent theoretical and experimental studies investigated a topological insulating phenomenon in the β-Ag 2 Te nanostructures, which consist of a fully filled insulating bulk state and a highly anisotropic massless Dirac cone of twodimensional surface states from the periodic quantum interference of electron phase.…”

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confidence: 99%

“…3,4 In particular, the monoclinic β-Ag 2 Te with low thermal conductivity has been concerned as one of promising thermoelectric materials and also employed to be a second-step host material chemically transformed into a series of metal tellurides. 4,5 In addition, recent theoretical and experimental studies investigated a topological insulating phenomenon in the β-Ag 2 Te nanostructures, which consist of a fully filled insulating bulk state and a highly anisotropic massless Dirac cone of twodimensional surface states from the periodic quantum interference of electron phase. 6,7 For enhancement in thermoelectric efficiency of the metal telluride nanostructures, researchers have predicted that onedimensional (1D) telluride nanostructures, including nanofibers, nanotubes and nanowire-based composites, would be advantageous over their bulk counterparts mainly due to the reduction of lattice thermal conductivity based on the stronger phonon-surface scattering.…”

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confidence: 99%

“…Due to the topotactic lattice matching between hexagonal t-Te and metal telluride crystal structures, such a structural conversion system has been reported to be thermodynamically favoured, and thus derive the self-templated transformation of Te nanowires into metal telluride nanowires. 4,5 Here, we should note that the specific morphology of metal telluride nanowires, not hollow nanofibers, were chemically transformed from the Te nanowires in a conventional chemical bath reaction. 5 This structural and morphological preservation in the chemical transformation from Te nanowires to Ag 2 Te nanowires may indicate the diffusion of Ag atoms into the layer structure of Te nanowires.…”

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