BiCuSeO Oxyselenides Research Articles

Realizing BiCuSeO-based thermoelectric device for ultrahigh carrier mobility through texturation

The thermoelectric conversion technology, as a promising renewable energy technology, enables direct and efficient conversion between electricity and heat. In the past ten years, there has been an increasing curiosity towards oxide thermoelectric materials due to their environmentally friendly nature, low cost, and excellent thermal and chemical stability. However, the intrinsic low carrier mobility of BiCuSeO limits its potential to be a high-performance thermoelectric material. Herein, we propose a dynamic sintering approach to enhance carrier mobility of BiCuSeO. As a result, carrier mobility at room temperature of three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 reaches an ultrahigh value of 13.1 cm2 V−1 s−1, which is the highest reported in the conventional doping of BiCuSeO system. Based on the ultrahigh carrier mobility, the power factor of three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 sample could reached 20 μV cm−1 K−2 near room temperature, and the average power factor of 300–923 K could reach 18.0 μV cm−1 K−2, effectively optimizing the electrical performance throughout the entire test temperature span. As a result, we successfully attain a ZT of ∼ 1.5 at 923 K and a ZTave of 0.89 within the temperature span of 300–923 K for three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 sample. Based on the outstanding performance, we have successfully built a 7-pair thermoelectric device based on three-step textured Bi0.94Pb0.06Cu0.97Se1.05O0.95 paired with the N-type two-step textured Bi2Te2.7Se0.3Cu0.01, which is the first BiCuSeO-based thermoelectric device. The thermoelectric device, exhibits a maximum conversion efficiency of 2.8 % at the temperature difference 215 K and simultaneously achieves a cooling temperature difference of 23.5 K with the hot end at 286 K. This work indicates that texturation is an effective approach for enhancing the carrier mobility of oxide TE materials. Besides, BiCuSeO oxyselenide is promising for pollution-free and cost-effective thermoelectric devices of power generation and cooling, thereby offering potential implications for sustainable energy solutions.

Modeling thermoelectric figure of merit of BiCuSeO oxyselenide ceramic using extreme learning machine computational method

BiCuSeO ceramic is an eco-friendly oxyselenide thermoelectric material that provides alternative directions for refrigeration and power generation through direct conversion between electrical and thermal energy. Aside from environmental friendliness of BiCuSeO ceramic, relatively cheap input materials, low toxicity, good thermal and chemical stability are among the unique features that contribute significantly to wider applicability of this material for energy conversion. The energy conversion efficiency of un-doped and pristine BiCuSeO thermoelectric material is very low while enhancement of its energy conversion efficiency has attracted serious attention from both experimental and theoretical perspectives thorough modulation doping, dual-vacancies creation and dual doping among others. This work models the thermoelectric figure of merit (energy conversion efficiency, ECE) of doped BiCuSeO based ceramics using extreme learning machine (ELM) with ionic radii and elemental concentrations predictors. ECE-SNELM model with sine activation function performs better than ECE-SGELM with sigmoid activation function using root mean square error (RMSE), correlation coefficient (CC) and mean absolute error (MAE) performance evaluation and assessment parameters with improvement of 20.61 %, 5.51 % and 5.77 %, respectively when computed using testing samples of BiCuSeO-based ceramics. Comparison of the developed ECE-SNELM and ECE-SGELM model with the existing machine learning (ML) based model shows that ECE-SNELM and ECE-SGELM model respectively outperforms ML (2022) model with improvement of 70.89 % and 35.8 % using RMSE metric. The developed ECE-T-SNELM model that includes temperature among its descriptors further outperforms the existing ML based model with improvement of 39.39 % on the basis of RMSE metric. The predictions of the developed models agree well with the measured values. The developed ECE-SNELM was further employed for investigating the behavior of BiCuSeO-based ceramics after dopant incorporation. The precision demonstrated by the developed ECE-SNELM and ECE-SGELM models in determining thermoelectric figure of merit of BiCuSeO-based ceramics is highly commendable and meritorious in strengthen energy conversion efficiency of the ceramics for addressing the global challenges of energy crisis.

Superior Carrier Mobility Enabled by the Charge Channel Leads to Enhanced Thermoelectric Performance in BiCuSeO Composites.

BiCuSeO oxyselenides possess a highlighted thermoelectric performance among oxides, which originates from their intrinsically low thermal conductivity. However, intrinsic factors causing low thermal transport are also detrimental to carrier transport, leading to ultralow carrier mobility and relatively low electrical transport properties. Here, high-conductivity single-wall carbon nanotubes (SWCNTs) are adopted as the charge channels to be embedded in a BiCuSeO-based matrix, providing a transport pathway for charge carriers. The results show that carrier mobility is increased to 188 cm2 V-1 s-1 due to the SWCNTs composited, triggering an enhancement in electrical transport properties. Besides, the SWCNTs embedded in the matrix introduce abundant interfaces, suppressing phonon transport and depressing lattice thermal conductivity. With these achievements, a maximum zT of 0.84 at 818 K is realized in the composite with 0.1wt% SWCNTs. The mechanical property of the composites is strengthened as well because of the SWCNTs. The work indicates that the SWCNTs, as the charge channels, propose an effective approach for enhancing carrier mobility in BiCuSeO-based materials, finally optimizing the thermoelectric performance as well as the mechanical property.

Synergistically optimized electron and phonon transport of p-type BiCuSeO oxyselenides via Pb dopant and Te composite

Layer-structured BiCuSeO oxyselenides with intrinsic low lattice thermal conductivity, non-toxicity, non-pollution and outstanding thermal stability is regarded as a promising thermoelectric material, but its application is limited by the poor electrical conductivity. In this paper, Pb-doped BiCuSeO (Bi1-xPbxCuSeO) was fabricated via a fast preparation method combined self-propagating high-temperature synthesis (SHS) with spark plasma sintering (SPS). Although Pb doping could greatly improve the electrical conductivity of BiCuSeO, the thermal conductivity increased as well, and it limits the thermoelectric performance. To further optimize the electron and phonon transport properties, Te powders and Te nanowires were introduced in Bi0·9Pb0·1CuSeO by ball milling, respectively. As a result, the thermal conductivity largely decreased with a maintained electrical performance. Ultimately, a maximum ZT value of 1.0 at 873 K was achieved for the 5 vol% Te nanowire + Bi0·9Pb0·1CuSeO sample, which is about 2.5 times as large as that for pristine BiCuSeO. Our work paves an alternative strategy for tuning the thermoelectric performance of BiCuSeO through Bi site doping combined low-dimension nanocomposites.

Thermoelectric properties of Sm-doped BiCuSeO oxyselenides fabricated by two-step reactive sintering

Among layered oxygen-containing compounds, BiCuSeO is one of the most promising candidates for thermoelectric applications due to its intrinsically low thermal conductivity and good thermal stability. However, the rather poor electrical conductivity of pristine BiCuSeO hinders its potential. Further enhancement of the thermoelectric performance by single doping at Bi site is limited mainly due to dramatic decrease of carrier mobility. Thus, new strategies, such as dual doping or doping with variable-valence elements seem to be promising. Along with that, the development of a fast and scalable synthesis route is essential for the industrial-scale fabrication of thermoelectric materials. Hence, in this paper, Bi 1– x Sm x CuSeO samples (0 ≤ x ≤ 0.08) have been synthesized with a simple and scalable reactive sintering process. For comparison, Bi 1– x Sm x CuSeO oxyselenides were also obtained by the conventional solid-state route. Our results highlight that, Sm for Bi substitution increases the electrical conductivity by 1.5–2 times and decreases the Seebeck coefficient by ~1.4 times at 873 K for both series. Overall, considering the increase of lattice thermal conductivity upon doping and not optimized power factor, the figure of merit z T is reducing upon doping. • Sm-doped BiCuSeO oxyselenides fabricated by reactive sintering. • Sm doping leads to an increase of σ from 39 Ω –1 cm –1 to ~55 Ω –1 cm –1 at 873 K. • Quality factor is reduced upon Sm doping due to increase in κ and decrease of μ w .

Microwave Synthesis and Enhanced Thermoelectric Performance of p-Type Bi0.90Pb0.10Cu1-xFexSeO Oxyselenides.

BiCuSeO oxyselenide, one of the best oxygen-containing thermoelectric materials, is promising with great potential applications. In this work, we present a high ZT of >1.3 in Bi0.90Pb0.10Cu0.96Fe0.04SeO fabricated via microwave synthesis and subsequent spark plasma sintering (SPS). We added 3-4 atom % Fe to the Pb-doped BiCuSeO to regulate the hole carrier concentration and mobility to 0.8-1.0 × 1020 cm-3 and ∼40 cm2 V-1 S-1, respectively, achieving moderate electrical conductivity, high Seebeck coefficient, and low carrier thermal conductivity simultaneously in a dual-doped sample. Under the synergistic enhancement by stress field, dislocation, and nanophase, the lattice thermal conductivity of Bi0.90Pb0.10Cu0.96Fe0.04SeO is limited to 0.24-0.49 W m-1 K-1 at 300-873 K. The development of efficient preparation methods for high-performance thermoelectric materials is significant to promote the application of thermoelectric conversion technology.

Recent Developments and Progress on BiCuSeO Based Thermoelectric Materials

In this paper, a brief review of experimental studies aimed at creating highly efficient thermoelectric materials based on BiCuSeO layered oxyselenides is presented. A brief historical survey is given and the available data on crystal and electronic structures and thermoelectric properties of BiCuSeO oxyselenides is discussed. The main physical ideas and methods used to improve the thermoelectric efficiency of materials based on BiCuSeO are considered.

High thermoelectric properties of p-type BiCuSeO co−doped with Ca2+ and Ba2+

In this work, we prepare Ca2+ and Ba2+ co−doped BiCuSeO using a solid−state reaction, followed by spark plasma sintering. Ca2+/Ba2+ co−doping significantly increases the electrical conductivity through the increased hole concentration. In addition to the increased power factor, Ca2+/Ba2+ co−doping reduces the phonon thermal conductivity through grain refinement, increased porosity, and mass and strain field fluctuations. The combination of the largest power factor and the low phonon thermal conductivity for Bi0.80Ca0.10Ba0.10CuSeO yields the largest dimensionless figure−of−merit (ZT). The ZT of Bi0.80Ca0.10Ba0.10CuSeO (0.60) at 600 °C is two times larger than that of the undoped BiCuSeO (0.30) at 600 °C. We systematically discuss the effect of the Ca2+/Ba2+ co−doping on the thermoelectric properties of BiCuSeO oxyselenide.

Microwave synthesis combined with SPS sintering to fabricate Pb doped p-type BiCuSeO oxyselenides thermoelectric bulks in a few minutes

An efficient technique to fabricate BiCuSeO oxyselenides thermoelectric bulks is studied. Pb doped p-type BiCuSeO ingots are synthesized by microwave processing for 4 minutes and the bulk materials with 8.7~8.9 gcm−3 density are produced after spark plasma sintering for 5 minutes. The XRD and XPS detection results show that all the samples have nearly a single phase indexed to tetragonal BiCuSeO, and the peak positions of Pb 4f7/2 and 4f5/2 simple spin-orbit doublet peaks in Bi0.98Pb0.02CuSeO and Bi0.90Pb0.10CuSeO respectively are 137.93 and 142.76 eV, and 137.49 and 142.49 eV. Holes are the majority carriers with concentrations of 3.22 1020cm−³ ~2.40 1021cm−³ in the doped samples. Bi0.98Pb0.02CuSeO shows the highest ZT of 0.76 at 773 K and possible larger values can be achieved at a higher temperature. The fabricate technique described here showing great prospect in the research and manufacturing of thermoelectric bulks.

Direct synthesis of p-type bulk BiCuSeO oxyselenides by reactive spark plasma sintering and related thermoelectric properties

Herein, we demonstrate that BiCuSeO compound can be formed in bulk directly from the raw materials through reactive spark plasma sintering (RSPS) followed by ball milling and a second short spark plasma sintering step. Compared to BiCuSeO samples obtained by a conventional solid-state reaction, the electrical transport properties of the RSPS bulk were moderately affected by the sintering technique, while the lattice thermal conductivity was almost unaffected, and the figure of merit zT attained a value at 773 K comparable to state-of-the-art BiCuSeO. The results indicate a new scalable method for the preparation of oxyselenides.

Boosting thermoelectric performance of BiCuSeO by improving carrier mobility through light element doping and introducing nanostructures

Abstract BiCuSeO oxyselenides are promising thermoelectric materials because of their high stability and high thermoelectric performance. Here, a new approach is proposed that Li and Ca are incorporated into BiCuSeO to achieve synergistically optimized electrical and thermal transport properties. Arising from partial substitutions of Bi3+ by Ca2+ and Li+, the carrier concentration significantly increased because of massively introduced hole carriers. More importantly, we reveal that the carrier mobility can be enhanced by light element Li doping arising from largely reduced carrier scattering. The largest carrier mobility value reaches 8.06 cm2V−1s−1, which is significantly enhanced as compared with previously reported doped BiCuSeO. As a result, the electrical conductivity increases to 288 Scm−1 and the power factor reaches as high as 804 μW m−1K−2 at room temperature in Bi0.84Li0.08Ca0.08CuSeO, which is about 288 and 53 folds as compared with pristine BiCuSeO, respectively. Furthermore, Li and Ca codoping not only leads to dual-atomic point-defects scattering, but also can effectively scatter high-frequency phonons through introducing calcium oxide nanoprecipitates, resulting in a low lattice thermal conductivity (0.54 Wm−1K−1 at 873 K). The combination of optimized power factor and thermal conductivity contributes to a high thermoelectric figure of merit ZT (∼0.9 at 873 K) in Bi0.88Li0.06Ca0.06CuSeO. This study provides a new pathway for enhancing thermoelectric performance of BiCuSeO via light element doping and introducing nanostructures.

Enhanced thermoelectric performance of variable-valence element Sm-doped BiCuSeO oxyselenides

Here, the effects of variable-valence element Sm doping on the thermoelectric performance of BiCuSeO are studied. The Bi1-xSmxCuSeO (x = 0, 0.025, 0.05, and 0.10) oxyselenides were prepared by a two-step solid state reaction and spark plasma sintering. Experimental measurements and first-principles calculations indicated that Sm2+ and Sm3+ coexisted in the samples. The electrical conductivity of the Sm-doped samples was greater than that of pristine BiCuSeO mainly because the holes introduced by Sm2+ doping increased the carrier concentration, and the shift of the Fermi level by Sm3+ substitution changed the band gap. The combination of a moderate Seebeck coefficient and relativity low thermal conductivity, gave a maximum ZT value of 0.65 at 823 K for Bi0.975Sm0.025CuSeO, which is approximately 25 % higher than that of the pristine sample. This study indicates that doping with rare-earth variable-valence elements is an efficient approach to designing high-performance thermoelectric materials.

Enhancement of thermoelectric performances of BiCuSeO through Y doping and grain refining

Thermoelectric properties of BiCuSeO oxyselenide ceramics were improved combining Y doping and grain refinement. Bi1−xYxCuSeO (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) (called as BYCSO below) samples were prepared by mechanical alloying and resistance pressing sintering (RPS). The testing results indicate that Y doping can increase the carrier concentration and electrical conductivity, increase the thermal conductivity. On the basis of Y doping, grain refinement by increasing ball milling strength was indicated to increase the concentration of Cu vacancies, which enhanced the electrical conductivity and power factor, and reduce the thermal conductivity. Finally, the ZT value is increased to 0.93, which is 98% higher than that of the pure sample.

Ultrafast synthesis of Pb-doped BiCuSeO oxyselenides by high-energy ball milling

We report on the direct ultrafast synthesis of Pb-doped BiCuSeO oxyselenides by high-energy ball milling. We show that, contrary to the mechanical alloying sintering routes used in the previous reports which require 7–13 h to fabricate the BiCuSeO phase in powder form, this synthesis technique enables us to obtain pure phase materials at room temperature under air with milling time less than 60 min.

Preparation, Structure, and enhanced thermoelectric properties of Sm-doped BiCuSeO oxyselenide

The layered oxyselenide BiCuSeO was recently discovered to be a promising high thermoelectric material due to its intrinsically low thermal conductivity. However, the rather high electrical resistivity of undoped BiCuSeO may preclude its potential thermoelectric applications. Herein, we achieved enhanced thermoelectric performance in rare-earth Sm-doped BiCuSeO by the band structure engineering. The replacement of Bi3+ by Sm3+ leads to the improvement of electrical conductivity, from 34 S cm−1 for pristine BiCuSeO to 79 S cm−1 for that of Bi0.94Sm0.06CuSeO at 873 K. Coupled with the large Seebeck coefficient (251 μVK−1) and relatively low thermal conductivity (0.58 Wm−1K−1), the figure of merit ZT is significantly increased from 0.49 for pristine BiCuSeO to 0.74 for Bi0.94Sm0.06CuSeO at 873 K. According to the first-principles calculation, the enhanced thermoelectric properties was ascribed to the decreased band gap by the substitution of Sm. Upon 10%Sm substitution, the band gap of BiCuSeO decreases from 0.50 eV to 0.34 eV, which promotes the density of states near the Fermi level. The present study suggests that rare-earth element can be effective in modifying the band structure of BiCuSeO and thus improving its electronic transport properties.

Effect of high pressure on structure characteristics and electrical transport properties of layered BiCuSeO oxyselenides

Layered BiCuSeO oxyselenides were rapidly synthesized under different pressures, whereby investigating the effect of high pressure during preparation process on the crystal/band structure, microstructure, and electrical transport properties of obtained BiCuSeO compounds. The systematic variations for crystal structure and microstructure are achieved with increasing high pressure. Meanwhile, the band/electronic structures are indicated to be optimized due to the high-pressure effect, realizing an increase in band gaps and a decrease in effective masses, and thus effectively modulating the carrier concentration and mobility of BiCuSeO system. Based on the systematic tuning above, the electrical transport properties of BiCuSeO system present a significant improvement, obtaining a higher power factor of 80 μW m−1 K−1 at room temperature for the BiCuSeO prepared under 4 GPa.

Complex electronic structure and compositing effect in high performance thermoelectric BiCuSeO

BiCuSeO oxyselenides are promising thermoelectric materials, yet further thermoelectric figure of merit ZT improvement is largely limited by the inferior electrical transport properties. The established literature on these materials shows only one power factor maximum upon carrier concentration optimization, which is typical for most thermoelectric semiconductors. Surprisingly, we found three power factor maxima when doping Bi with Pb. Based on our first-principles calculations, numerical modeling, and experimental investigation, we attribute the three maxima to the Fermi energy optimization, band convergence, and compositing effect due to in situ formed PbSe precipitates. Consequently, three ZT peaks of 0.9, 1.1, and 1.3 at 873 K are achieved for 4, 10, and 14 at.% Pb-doped samples, respectively, revealing the significance of complex electronic structure and multiple roles of Pb in BiCuSeO. The results establish an accurate band structure characterization for BiCuSeO and identify the role of band convergence and nanoprecipitation as the driving mechanism for high ZT.

Highly enhanced thermoelectric performance in BiCuSeO ceramics realized by Pb doping and introducing Cu deficiencies

AbstractIn recent years, BiCuSeO oxyselenides have been developed as a promising thermoelectric material. In this article, PbxBi1−xCu1−ySeO (x = y = 0, 0.02, 0.04, 0.06, and 0.08) are prepared by solid‐state reaction method and spark plasma sintering (SPS), and the combinatorial effects of Pb doping and Cu deficiencies on thermoelectric properties are investigated systematically. The transport properties are significantly enhanced due to the optimized carrier density, majorly contributing to the promotion of ZT values. As a result, the maximum ZT of 0.77 at 873 K and average ZT (from 300 to 873 K) of 0.50 are obtained for Pb0.06Bi0.94Cu0.94SeO sample. The values are 0.4 and 1.2 times, respectively, higher than that of pristine sample.

Reactive spark plasma sintering and thermoelectric properties of Nd-substituted BiCuSeO oxyselenides

Bi1-xNdxCuSeO (x = 0; 0.05; 0.10; 0.15) was fabricated by the solid-state reaction and the reactive spark plasma sintering for comparative study. It was demonstrated that BiCuSeO could be formed in-situ by the reaction between Bi2O3, Bi, Cu and Se during the densification process. The effect of Nd doping on the thermoelectric properties has been investigated. The results indicated that for both series of the samples the substitution of Bi3+ by Nd3+ resulted in the increase of charge carrier concentration mainly caused by Bi/Cu deficiencies formation with the substitution. However, the specimens obtained by reactive spark plasma sintering had lower hole concentration which may originate from the high speed of the process resulted in induced point defect and interface scattering and another phase formation mechanism leading to the smaller amount of Bi/Cu deficiencies.

Enhanced thermoelectric performance in BiCuSeO oxyselenides via Ba/Te dual-site substitution and 3D modulation doping

Here, Bi1-xBaxCuSe1-xTexO (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics have been prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process. The effects of Ba/Te doping on the thermoelectric properties have been investigated systematically. For Ba doping, it can tune the Fermi level and promote the band convergence, decreasing the band gap and significantly enhancing the carrier concentration; for the Te doping based on Ba doping, it can profoundly reduce the difference of electronegativity in (Cu2Se2)2- layer, increase bond covalency, and then increase the electrical conductivity. The results indicate that the substitution of Ba/Te resulted in significant increases of electrical conductivity and power factor. Based on this, modulation doping leads to the simultaneous increase of the electrical conductivity and Seebeck coefficient. Finally, the maximum power factor of 0.98 mW m−1 K−2 and ZT value of 1.17 were obtained for the modulation doped Bi0.90Ba0.10CuSe0.90Te0.10O bulk, which were ~ 3.5 and ~ 2.2 times respectively as those of the pristine BiCuSeO ceramic.