Ionic conduction and chemical diffusion in solid solutions of superionic conductors Cu2X-Me2X (Me = Ag, Li; X = S, Se)

Балапанов, М. Х.; Zinnurov, I. B.; Mukhamed’yanov, U. Kh.

doi:10.1134/s1023193507050138

Cited by 14 publications

(14 citation statements)

References 7 publications

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“…On the positive side, Balapanov et al have previously reported suppressed ionic conductivity and cation diffusivity in Cu 2-x Se by substituting copper with lithium [16] (Fig.1). This behavior indicates that it might be possible to chemically tune the cation diffusivity in Cu 2-x Se to a level where it could be countered by using longer leg segments (which will decrease the thermal or electric potential gradients driving migration).…”

mentioning

confidence: 99%

Enhanced stability and thermoelectric figure-of-merit in copper selenide by lithium doping

Kang

Pöhls

Aydemir

et al. 2017

Materials Today Physics

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Superionic thermoelectric materials have been shown to have high figure-ofmerits, leading to expectations for efficient high-temperature thermoelectric generators. These compounds exhibit extremely high cation diffusivity, comparable to that of a liquid, which is believed to be associated with the low thermal conductivity that makes superionic materials good for thermoelectrics. However, the superionic behavior causes cation migration that leads to device deterioration, being the main obstacle for practical applications. It has been reported that lithium doping in superionic Cu 2-x Se leads to suppression of the Cu ion diffusivity, but whether the material will retain the promising thermoelectric properties had not yet been investigated. Here, we report a maximum zT > 1.4 from Li 0.09 Cu 1.9 Se, which is higher than what we find in the undoped samples. The high temperature effective weighted mobility of the doped sample is found higher than Cu 2-x Se, while the lattice thermal conductivity remains similar. We find signatures of suppressed bipolar conduction due to an enlarged band gap. Our findings set forth a possible route for tuning the stability of superionic thermoelectric materials.Thermoelectric generators produce electrical energy from a heat flux through the device. Having been proven for their reliability from stable implementations in space missions, the technology is now drawing interest for terrestrial applications. For example, using thermoelectric technology to convert waste industrial heat into electricity could deliver a significant alleviation to the energy crisis. However, wide-spread use of the technology is limited by the energy conversion efficiency, which is bottlenecked by what thermoelectric materials can offer. The maximum efficiency obtainable from a material is characterized by the figure-of-merit:where S is the Seebeck coefficient, σ is electrical conductivity, and κ is thermal conductivity. Thermoelectric materials research is thus heavily focused on the search for high zT materials. In the search for new material families for thermoelectrics, the revisit to superionic compounds as thermoelectric materials [1] has sparked great interest because of their inherently low thermal conductivity [2] which is advantageous in obtaining a high zT . In the superionic phase, cations exhibit liquid-like diffusivity [3,4] and this disordered nature typically results in a very low lattice thermal conductivity (<1 W m −1 K −1 ). Many of the superionic compounds, particularly those that are also good electric conductors, indeed show promising thermoelectric properties as exemplified by Cu 2 Se [1,5]

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confidence: 99%

Enhanced stability and thermoelectric figure-of-merit in copper selenide by lithium doping

Kang

Pöhls

Aydemir

et al. 2017

Materials Today Physics

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“…From Figure 2, the highest ionic conductivity is shown by Cu 2 Se copper selenide, and the lowest one is observed for Li 0.25 Cu 1.75 Se , so, in general, doping with lithium leads to a decreasing of the ionic conductivity. It was previously established that lithium ions over-lap the light diffusion pathways of copper ions in copper selenide, decreasing ionic conductivity [33,34]. The non-stoichiometry degree of the composition must also be taken into account, since it is known that the ionic conductivity of Cu 2−σ Se decreases with non-stoichiometry degree σ increasing [17], followed by decreasing the concentration of mobile copper ions.…”

Section: Resultsmentioning

confidence: 99%

“…Substitution by lithium revealed a significant decrease in both the ionic and the electronic conductivity, a decrease of the self-diffusion coefficients of cations and the chemical diffusion coefficients [32][33][34][35][36], while maintaining and even increasing the electronic Seebeck coefficient were observed.…”

Section: Introductionmentioning

confidence: 99%

Effect of lithium doping on electrophysical and diffusion proper-ties of nonstoichiometric superionic copper selenide Cu1.75Se

Balapanov¹,

Kuterbekov²,

Kubenova³

et al. 2017

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The results of studies of the ionic conductivity and the conjugated chemical diffusion coefficients (CCDC) in the nonstoichiometric Li x Cu 1.75 Se (0 ≤ x ≤ 0.25) ternary alloys are presented. It has been observed that the values of the ionic conductivity of Cu 1.75 Se copper selenide decreases with lithium doping in general owing to increasing the the activation energy. The increasing of the conjugate chemical diffusion coefficients of the cations and electron holes was observed with increasing of lithium content, despite the decreasing of self-diffusion coefficients of the cations and decreasing of electron mobilities. The behavior of the conjugate chemical diffusion coefficients explained by a decrease in the degree of non-stoichiometry of the composition, leading to an increase of the internal electric field accelerating the motion of slower particles.

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“…It is believed that the superionic diffusion of Cu ions, which suppresses the lattice thermal conductivity, plays an essential role in the high TE performance of Cu2X materials [6,11,19,[21][22][23][24][25][26][27]. While the detailed structure and liquid-like behavior of Cu ions have been carefully studied in Cu2Se [6,10,26,28,29], the investigation on the electronic properties of Cu2Te is essentially lacking up to date, although the Cu ions are expected to be more mobile in Cu2Te due to the weaker ionic bonds.…”

Section: Introductionmentioning

confidence: 99%

Measurement of electronic structure and surface reconstruction in the superionic Cu2−xTe

et al. 2021

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Recently, layered copper chalcogenides Cu2X family (X=S, Se, Te) has attracted tremendous research interests due to their high thermoelectric (TE) performance, which is partly due to the superionic behavior of mobile Cu ions, making these compounds "phonon liquids". Here, we systematically investigate the electronic structure and its temperature evolution of the less studied single crystal Cu2-xTe by the combination of angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscope/spectroscopy (STM/STS) experiments. While the band structure of the Cu2-xTe shows agreement with the calculations, we clearly observe a 2 × 2 surface reconstruction from both our low temperature ARPES and STM/STS experiments which survives up to room temperature. Interestingly, our low temperature STM experiments further reveal multiple types of reconstruction patterns, which suggests the origin of the surface reconstruction being the distributed deficiency of liquid-like Cu ions. Our findings reveal the electronic structure and impurity level of Cu2Te, which provides knowledge about its thermoelectric properties from the electronic degree of freedom.

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Ionic conduction and chemical diffusion in solid solutions of superionic conductors Cu2X-Me2X (Me = Ag, Li; X = S, Se)

Cited by 14 publications

References 7 publications

Enhanced stability and thermoelectric figure-of-merit in copper selenide by lithium doping

Enhanced stability and thermoelectric figure-of-merit in copper selenide by lithium doping

Effect of lithium doping on electrophysical and diffusion proper-ties of nonstoichiometric superionic copper selenide Cu1.75Se

Measurement of electronic structure and surface reconstruction in the superionic Cu2−xTe

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