Thermoelectric Properties Of Cu1 Research Articles

Phase composition and thermoelectric properties of Cu–Ag–Se films with different Ag content

In this study, a series of Cu–Ag–Se films were prepared on Si (100) substrate by magnetron sputtering. The phase composition, micro-structure and thermoelectric properties were studied. The results showed that the phase composition of deposited Cu–Ag–Se films varied from β-Cu2-xSe and a small amount of CuAgSe phase to majority β-Cu2-xSe and minority CuAgSe phase, minority β-Cu2-xSe and majority CuAgSe phase, CuAgSe and a small amount of β-Cu2-xSe phase, Ag2Se and a small amount of CuAgSe +β-Cu2-xSe phase as Ag content increased from 0.4 to 17.0, 20.8, 29.5, 41.4 at.%, respectively. In the deposited Cu–Ag–Se films, the carrier concentration first decreased and then increased and the mobility displayed an opposite trend with increasing CuAgSe content (decreasing β-Cu2-xSe content). The room temperature electrical conductivity and absolute value of room temperature Seebeck coefficient gradually increased with increasing CuAgSe content for the deposited Cu–Ag–Se films. The power factor of 29.5 at.% Ag samples (CuAgSe phase films) at whole measured temperature was the highest in all samples due to high Seebeck coefficient and high electrical conductivity, resulting in the highest PF value of 2.05 mW m−1 K−2 at 62 °C. However, due to its high thermal conductivity of 10.93 W m−1K−1, the room temperature ZT value of this sample was only 0.05 even if it possessed a higher PF value. Ag2Se phase films possessed the lowest PF value due to their lower Seebeck coefficient even if they possessed higher electrical conductivity.

Theoretical Study of Intrinsic and Extrinsic Point Defects and Their Effects on Thermoelectric Properties of Cu2SnSe3.

Current understanding of the intrinsic point defects and potential extrinsic dopants in p-type Cu2SnSe3 is limited, which hinders further improvement of its thermoelectric performance. Here, we show that the dominant intrinsic defects in Cu2SnSe3 are CuSn and VCu under different chemical conditions, respectively. The presence of VCu will damage the hole conduction network and reduce hole mobility. Besides, we find that the substitution of Al, Ga, In, Cd, Zn, Fe, and Mn for Sn can inhibit the formation of VCu; introducing CuSn, FeSn, MnSn, and NiCu defects can significantly enhance electronic density of states near the Fermi level due to the contribution of 3d orbitals. Therefore, increasing the Cu content and/or introducing the above beneficial dopants appropriately are expected to cause enhancement of carrier mobility and/or thermopower of Cu2SnSe3. Furthermore, introducing AgCu, AlSn, ZnSn, GeSn, and MnSn defects can induce large mass and strain field fluctuations, lowering lattice thermal conductivity remarkably. Present results not only deepen one's insights into point defects in Cu2SnSe3 but also provide us with a guide to improve its thermoelectric properties.

Altering the high-temperature stability and thermoelectric properties of Cu1.8S thermoelectric materials by Se incorporation

Thermoelectric materials based on Cu 1.8 S are not hampered by electric-field-driven degradation in real applications, but their high-temperature applications are problematic owing to their tendency to oxidize or spontaneously decompose. Here, we reveal that Cu 1.8 S powder is gradually oxidized to form a mixture of Cu 2 O, Cu(SO 4 ), and Cu 2 O(SO 4 ) at high temperatures under air. Although a dense oxide film is formed on the surface of the sintered Cu 1.8 S block at high temperature, hindering the oxidation process, the brittle oxide film fails to inhibit the spontaneous decomposition of the Cu 1.8 S block into the Cu 1.96 S phase and S vapor at high temperatures. Thus, Cu 1.8 S thermoelectric materials are unsuitable for applications above 300 °C in air. To address this issue, we partially replaced S atoms with Se; the sintered Cu 1.8 S 0.8 Se 0.2 blocks exhibited significantly increased anti-oxidation and anti-decomposition capacities in air. In addition, we found that the thermoelectric figure of merit of the sintered Cu 1.8 S 0.8 Se 0.2 block was 47% higher than that of traditionally prepared, pure Cu 1.8 S at 450 °C. • The Cu 1.8 S block cannot function stably at temperatures over 300 °C. • The anti-oxidation and anti-decomposition capacities of the Cu 1.8 S 0.8 Se 0.2 are improved. • The ZT of the Cu 1.8 S 0.8 Se 0.2 is 117% higher than that of pure Cu 1.8 S at 450 °C.

Low-temperature acanthite-like phase of Cu2S : Electronic and transport properties

The mobility and disorder in the lattice of Cu atoms as liquid-like behavior is an important characteristic affecting the thermoelectric properties of Cu$_{2}$S. In this study, using a theoretical model called acanthite-like structure for Cu$_{2}$S at a low-temperature range, we systematically investigate the electronic structure, intrinsic defect formation, and transport properties by first-principles calculations. Thereby, previous experimental reports on the indirect bandgap nature of Cu$_{2}$S were confirmed in this work with an energy gap of about 0.9-0.95 eV. As a result, the optical absorption coefficient estimated from this model also gives a potential value of $\alpha > 10^{4}$ cm$^{-1}$ in the visible spectrum range. According to the bonding analysis and formation energy aspect, Cu vacancy is the most preferred defect to form in Cu$_{2}$S, which primarily affects the conductive behavior as a $p$-type, as experimentally observed. Finally, the transport properties of Cu$_{2}$S system were successfully reproduced using an electron-phonon scattering method, highlighting the important role of relaxation time prediction in conductivity estimation instead of regarding it as a constant.

Effect of Te and In Co-doping on Thermoelectric Properties of Cu2SnSe3 Compounds

Effect of Te and In Co-doping on Thermoelectric Properties of Cu₂SnSe₃ Compounds

Enhanced Thermoelectric Properties of Cu x Se (1.75≤ x ≤2.10) during Phase TransitionsSupported by the National Key Research and Development Program of China (Grant No. 2018YFB0703600), the National Natural Science Foundation of China (Grant Nos. 91963208, 51625205, 51961135106, and 51902199), Shanghai Government (Grant No. 20JC1415100), the CAS-DOE Program of Chinese Academy of Sciences (Grant No. 121631KYSB20180060), and the Shanghai Sailing

Coupling of a phase transition to electron and phonon transports provides extra degree of freedom to improve the thermoelectric performance, while the pertinent experimental and theoretical studies are still rare. Particularly, the impaction of chemical compositions and phase transition characters on the abnormal thermoelectric properties across phase transitions are largely unclear. Herein, by varying the Cu content x from 1.75 to 2.10, we systemically investigate the crystal structural evolution, phase transition features, and especially the thermoelectric properties during the phase transition for Cu x Se. It is found that the addition of over-stoichiometry Cu in Cu x Se could alter the phase transition characters and suppress the formation of Cu vacancies. The critical scatterings of phonons and electrons during phase transitions strongly enhance the Seebeck coefficient and diminish the thermal conductivity, leading to an ultrahigh dimensionless thermoelectric figure of merit of ∼1.38 at 397 K in Cu2.10Se. With the decreasing Cu content, the critical electron and phonon scattering behaviors are mitigated, and the corresponding thermoelectric performances are reduced. This work offers inspirations for understanding and tuning the thermoelectric transport properties during phase transitions.

Minimizing Thermal Conductivity for Boosting Thermoelectric Properties of Cu–Ni-Based Alloys through All-Scale Hierarchical Architectures

Constantan (Cu–Ni alloy) is widely used in the field of thermocouples due to its excellent thermoelectric and mechanical properties. To broaden the application area, the intrinsically high thermal ...

Off-stoichiometry effects on the thermoelectric properties of Cu2+δSe (−0.1 ≤δ≤ 0.05) compounds synthesized by a high-pressure and high-temperature method

The chemical composition can directly tune the transport properties of Cu2Se liquid-like materials, including the carrier concentration, carrier mobility and superionic feature.

Effects of sintering temperature on thermoelectric properties of Cu1.8S bulk materials

Due to the excellent electrical transmission and potentially excellent thermoelectric (TE) performance, digenite (Cu1.8S) has attracted more attentions. The combination of mechanical alloying (MA) and spark plasma sintering (SPS) was widely used in preparing Cu1.8S bulk material, while the TE properties for pure sample were still low. Therefore, it’s worth to search a suitable synthesis method to enhance the thermoelectric performance for pristine Cu1.8S material. In this study, high-density bulk samples of copper sulfide (CS) were fabricated by solid states reaction method combined with SPS at different temperatures. When the SPS temperature was over 873 K, large amounts of sulfur volatilization lead to the appearance of Cu1.96S second phase and it was considered to have great influence on the thermoelectric performances. The result reveals that the increased sintering temperature could affect the density and grain size of the bulk samples. The highest ZT value of 0.54 was obtained at 773 K for the sample sintered at 773 K, which is also the highest ZT value for the pristine Cu1.8S in the literature.

Eco-friendly compound Cu2SnS3 shows promise as a thermoelectric material

Scientists explore the thermoelectric properties of Cu 2 SnS 3 by systematically varying its copper and tin content and studying its band structure and transport properties.

Preparation and thermoelectric properties of Cu1.8S/CuSbS2 composites

Chalcostibite (CuSbS2) is composed of earth-abundant elements and has a proper band gap (Eg = 1.05 eV) as a thermoelectric (TE) material. Herein, we report the TE properties in the CuSbS2based composites with a mole ratio of (1−x)CuSbS2−xCu18S (x = 0, 0.1, 0.2, 0.3), which were prepared by mechanical alloying (MA) combined with spark plasma sintering (SPS). X-ray diffraction (XRD) and back-scattered electron image (BSE) results indicate that a single phase of CuSbS2 is synthesized at x = 0 and the samples consist of CuSbS2, Cu3SbS4, and Cu12Sb4S13 at 0.1 ⩽ x ⩽ 0.3. The correlation between the phase structure, microstructure, and TE transport properties of the bulk samples is established. The electrical conductivity increases from 0.14 to 50.66 S·cm−1 at 723 K and at 0 ⩽ x ⩽ 0.03, while the Seebeck coefficient holds an appropriate value of 190.51 µV·K−1. The highest ZT value of 0.17 is obtained at 723 K and at x = 0.3 owing to the combination of a high PF 183 µW·m−1·K−2 and a low κ 0.8 W·m−1·K−1.

Structural and Thermoelectric Properties of Cu Substituted Type I Clathrates Ba₈CuxSi~32-xGa~14.

With an attempt to improve the thermoelectric properties of type I clathrates in the Ba-Ga-Si system, we introduce Cu into the framework of the crystal structure. Single crystals are prepared in Ga-flux and characterized by X-ray diffraction techniques and transport measurements for the structural and thermoelectric properties. Our composition analyses show that only a small amount of Cu is determined in the clathrates. The single crystal X-ray diffraction data refinements confirm that Ga atoms prefer the 6c and 24k sites and avoid the 16i sites in the crystal structure. The small amount of Cu affects the crystal structure by compressing the tetrakaidecahedral cage along the direction perpendicular to the six-atom-ring plane. This could be the reason for the high charge carrier concentration, and low electrical resistivity and Seebeck coefficient. We analyze the principal mechanism for our observation and conclude that the Cu substitution can adjust some subtle details of the structure, maintaining the Zintl rule in the type I clathrates.

Morphology and phase evolution from CuS to Cu1.8S in a hydrothermal process and thermoelectric properties of Cu1.8S bulk

CuS microflowers self-assembled from nanosheets were prepared by hydrothermal synthesis (HS) using CuCl2·2H2O and CS(NH2)2 as raw materials and glycol as a solvent at 120 and 140 °C for 1.5 h.

Investigation on the structure and thermoelectric properties of CuxTe binary compounds.

Cu2Te is a superionic conductor that belongs to the Phonon Liquid Electron Crystal class of thermoelectric (TE) materials. Despite the simple chemical formula, the crystal structures and phases in the Cu2Te system have not been understood properly. In this work, we study the structural and TE properties of Cu2Te (CT2), Cu1.6Te (CT1.6) and Cu1.25Te (CT1.25). The samples were synthesized via a solid-state reaction method. Powder X-ray diffraction analysis revealed that the samples have different crystal structures depending upon the Cu : Te stoichiometry. The elemental compositional analysis showed that all the samples are copper deficient. This is due to the precipitation of metallic copper on the surface of the ingot arising from the thermal dissociation of Cu2Te. The transport properties were measured in the temperature range 300 K-600 K. The electrical conductivity (σ) decreases with an increase in temperature indicating a metal-like behaviour for all the samples. The positive Seebeck coefficients (S) for all the samples indicates that majority charge carriers are holes. The sample CT2 has a higher S (29.5 μV K-1 at 573 K) and a lower σ (2513 S cm-1 at 573 K) due to a lower carrier (hole) concentration compared to the other two samples. With the increase in Cu deficiency, the hole concentration increases, and this leads to higher electronic thermal conductivity in the samples CT1.6 and CT1.25. The maximum thermoelectric figure of merit of 0.03 at 524 K is achieved for the sample CT2 owing to its higher power factor (0.24 mW m-1 K-2) and lower thermal conductivity (3.8 W m-1 K-1). The present study bridges the gap between the theoretical predictions and experimental observations involving the various possible structures in this system. Furthermore, we have shown that the Cu vacancies are detrimental to the thermoelectric performance of Cu2Te.

Thermoelectric Properties of Cu1.98Se Prepared by Melt-spinning Process

Thermoelectric Properties of Cu1.98Se Prepared by Melt-spinning Process

Facile synthesis and thermoelectric properties of Cu1.96S compounds

Cu2-xS compounds with low-cost and low-toxicity elements have been reported as good candidates for thermoelectric (TE) application. In this work, the Cu1.96S powders were synthesized by both hydrothermal synthesis (HS) and mechanical alloying (MA) methods. The HS synthesis process and mechanism was discussed in detail. The polycrystalline Cu1.96S bulk materials were obtained by condensing the powders (prepared by HS and MA) or the mixed HS and MA powers with the different ratio (1:0, 9:1, 1:9 and 0:1) using spark plasma sintering (SPS) technique. The phase structure, microstructure of the powders and bulk samples were checked. The results show that the Cu1.96S powders synthesized by HS are more stable than the powder prepared by MA method during the SPS process. And the thermoelectric properties of all bulk samples were investigated in detail at the temperature ranges from 323 to 773 K. The Cu1.96S bulk sample sintered by using mixed powders of 90 wt% HSed powders and 10 wt% MAed powders obtained the maximum ZT value of 1.01 at 773 K, which is currently the highest reported value for the Cu1.96S system at this temperature.

Effects of second phases on thermoelectric properties in copper sulfides with Sn addition

Abstract

Enhanced thermoelectric properties of Cu doped ZnSb based thin films

Cu doped ZnSb based thin films were deposited by direct current magnetron co-sputtering. X-ray diffraction results show that the un-doped thin film reveals a single ZnSb phase and it transforms to Zn4Sb3 phase after Cu doped. The material with Zn4Sb3 phase which belongs to R-3c space group crystal will lead to lower thermal conductivity. The Hall effect measurement shows that the samples are P-type semiconductors. The electrical conductivity increasers after Cu doped due to the increase of carrier concentration and the improvement in crystallinity. Though the Seebeck coefficient decreases after Cu doped, the ZT value increases from 0.11 to 0.43 with higher electrical conductivity and lower thermal conductivity at room-temperature. The temperature-dependent of ZT value is estimated to be ∼1.35 for the thin film with Zn4Sb3 phase by using the bulk lattice thermal conductivity together with the thin film electrical thermal conductivity.

Assessing the thermoelectric properties of CuxO (x = 1 to 2) thin films as a function of composition

Series of CuxO thin-films in the entire range of compositions 1≤x≤2 were obtained by varying the oxygen flux in an rf-sputter deposition process. Growth windows for three crystalline phases, i.e., the thermodynamically stable cuprous oxide Cu2O and cupric oxide CuO as well as the metastable paramelaconite Cu4O3, were observed. The crystalline phases persist non-stoichiometrically over a wide range of compositions. These flux-range windows are separated by ranges where highly disordered, almost amorphous material is obtained. All samples were analysed with respect to their thermoelectric properties, i.e., Seebeck coefficient, electrical, and thermal conductivity. Clear trends of these transport parameters were found and used to determine the thermoelectric figure of merit ZT. The ZT-values at room temperature are highest for the two thermodynamically stable crystalline phases CuO and Cu2O.

Thermoelectric properties of Cu and Cr disordered CuCrX2(X=S, Se): a first principles study

The layered antiferromagnetic ACrX2 -type compounds are currently highlighted as prominent material candidates for low- and intermediate-temperature thermoelectric (TE) applications. A key to attain the enhanced TE characteristics is to apply high-temperature sintering which presumably introduces some cation disorder. Here we present spin unrestricted density functional theory analysis of electronic band structures and TE properties of Cu and Cr disordered CuCrX2(X = S, Se) phases. A narrow band gap semiconductor to metal transition is observed on 8.3% Cr-site disorder for both the compounds, X = S and Se. The large p-type Seebeck coefficient realized in the metallic state for the Cr-disordered phases is the factor that makes these phases promising TE materials. These theoretical findings for the Cr-disordered phases are well in line with reported experimental data for electronic transport properties. Contrarily, the results revealed for the Cu-disordered phases do not agree with the experimental data. Hence the results of our theoretical analysis strongly point towards the Cr rather than the Cu disorder picture to explain the TE electronic transport characteristics of the high-temperature sintered phases of CuCrX2(X = S, Se).