Bi2Te3 Nanocomposites Research Articles

Dual-phase competitive behavior in N-type Sn–Bi–Te thermoelectric films achieving high thermoelectric performance

The dual-phase competitive behavior is introduced as an effective strategy to optimize the physical and chemical properties of N-type Bi2Te3 thermoelectric (TE) materials. Controllable SnTe-embedded Bi2Te3 nanocomposites can be synthesized with the addition of excessive Sn into Bi2Te3 by tuning the crystallization behavior under proper thermal heating temperature. Notably, the precipitation temperature of Bi2Te3 increases from 473 ​K for Sn20.9(Bi2Te3)79.1 to 573 ​K for Sn34.4(Bi2Te3)65.6, expanding the controllable temperature span for the presence of SnTe phase. The second-phase nanoprecipitate SnTe can improve electrical conductivity by competing with the Bi2Te3 phase, achieving an increase of four orders of magnitude at the critical temperature of ∼500 ​K. Simultaneously, it increases the interfacial energy filtration effect between nanocrystalline grains, decoupling electrical parameters between conductivity and Seebeck coefficient. Consequently, the high power factor of ∼147 ​μW/mK2 at 650 ​K for optimized Sn26.6(Bi2Te3)73.4 films can be obtained, which is more than twice that of the pure Bi2Te3 material. Our work demonstrates a new physical mechanism to unravel the complicated structure-property relationship by dual-phase competitive behavior during phase transition. This study fills the gap in knowledge on the effects of the SnTe phase regarding the Bi2Te3 system and provides guidance for the innovative design of high-performing inorganic thermoelectrics.

Synthesis and Characterization of SiO2-Based Graphene Nanoballs Using Copper-Vapor-Assisted APCVD for Thermoelectric Application.

This study describes a method by which to synthesize SiO2-based graphene nanoballs (SGB) using atmospheric pressure chemical vapor deposition (APCVD) with copper vapor assistance. This method should solve the contamination, damage, and high costs associated with silica-based indirect graphene synthesis. The SGB was synthesized using APCVD, which was optimized using the Taguchi method. Multiple synthesis factors were optimized and investigated to find the ideal synthesis condition to grow SGB for thermoelectric (TE) applications. Raman spectra and FESEM-EDX reveal that the graphene formed on the silicon nanoparticles (SNP) is free from copper. The prepared SGB has excellent electrical conductivity (75.0 S/cm), which shows better results than the previous report. Furthermore, the SGB nanofillers in bismuth telluride (Bi2Te3) nanocomposites as TE materials exhibit a significant increment in Seebeck coefficients (S) compared to the pure Bi2Te3 sample from 109 to 170 μV/K at 400 K, as well as electrical resistivity decrement. This approach would offer a simple strategy to improve the TE performance of commercially available TE materials, which is critical for large-scale industrial applications.

Mechanochemical Synthesis and DC Electrical Conductivity of PANI-Based MWCNT Containing Nanocomposites with Te0 and Bi2Te3 Thermoelectric Nanophase

Nowadays, the search for the coupled polymer nanocomposite thermoelectrics that exhibit a high value of thermoelectric figure of merit (ZT) and similar behaviour of physical properties for the use as legs of thermoelectric cells is a current challenge. The direct current (DC) conductivity is one of the three important components of thermoelectric figure of merit. The aim of this study was to obtain PANI-based nanothermoelectrics with Te0 and Bi2Te3 nanoparticles and MWCNT by mechanochemical methodology and to investigate the dependency of their DC electrical conductivity on temperature in the 298–353 K range using the Arrhenius and Mott’s variable range hopping (VRH) models. Inorganic Te0 and Bi2Te3 nanoparticles were pre-synthesized by the available and environmentally friendly method using a commercial tellurium powder. The samples obtained were characterized by X-ray diffractometry (XRD), IR and UV-Vis spectroscopy. The XRD study of ES-PANI/Te0 (4.4 wt% Te0) and ES-PANI/Bi2Te3 (2.9 wt% Bi2Te3) nanocomposites found that the nanoparticle average size was 32 nm and 17 nm, respectively. The DC conductivity study of the samples with different nanophase content (2.1, 4.4, 10.2 wt% Te0, 1.5, 2.9, 7.3 wt% Bi2Te3, 1.5 wt% MWCNT) by the two points measurement method reveals the following: (a) the presence of inorganic nanophase reduces the conductivity compared to the matrix, (b) the addition of MWCNT in ES-PANI increases its electrical conductivity, (c) the conductivity of ES-PANI/Te0 as well as ES-PANI/Bi2Te3 nanocomposite rises with the increasing inorganic nanophase content, (d) the observed increase in the electrical conductivity of MWCNT-based nanocomposites with increasing inorganic nanophase content is interrupted by a characteristic area of decrease in its value at average values of inorganic nanoparticles content (at Te0 content of 4.4 wt%, at Bi2Te3 content of 2.9 wt%), (e) a similar DC conductivity behaviour in ES-PANI/Te0—ES-PANI/Bi2Te3 and ES-PANI/Te0-MWCNT—ES-PANI/Bi2Te3-MWCNT nanocomposite pairs is observed.

(Invited) Thermoelectric Micropower Devices for Iot Sensing

Novel electrochemical processes of Bi2Te3 nanocomposites been developed for thermoelectric power generators (TEGs) with a high figure of merit (ZT) at room temperature. Nanoparticles or/and carbon nanomatrials are dispersed in an electrolyte for electrodeposition, and co-electrodeposition is performed to make a thin or thick film. The small grained nanocomposite film is formed by the inclusion of the nanoparticles or/and carbon nanomaterials. Reduction of thermoelectric properties can be observed because of the phonon scattering with the nanostructures. In addition, nanomaterials inclusion can change the carrier density of the composite films, thus, appropriate density of inclusion can improve the performances of the electrical conductance and Seebeck coefficient. Maximum ZT ~1 is obtained by optimization of the deposition condition, which is 6 times higher than that of reported pristine Bi2Te3 deposited by electrodeposition also higher value than that of bulk Bi2Te3 (0.7~0.8).In addition, TEGs are fabricated for energy harvester applications to IoT sensors. The system consists ofThose results show that this deposition methods have a high potential ability to manufacture the micro TEG for energy harvesting devices. Based on assembling process using electrodeposited thermoelectric thick films, TEGs are constructed, and applied to wireless sensors. Without primary battery, the sensors can works near room temperature for a long time. Figure 1

Tuned Fermi Level and Improved Thermoelectric Performance in Bi2Te3 Nanocomposites Reinforced with g-C3N4 Nanosheets

Bi2Te3 has been recognized as an efficient and scalable thermoelectric material suitable for sustainable power generation and environment friendly cooling. Nano structuring and adding nano inclusions in the bulk thermoelectric material offers cost effective and scalable strategy to attain reduced thermal conductivity and improved figure of merit. Here, we report inclusion of g-C3N4 nanosheets in Bi2Te3 to tune the thermoelectric properties of the matrix. The g-C3N4/Bi2Te3 nanocomposites were synthesized through solid state reaction route, ball milling and hot pressing techniques. The fermi level shift is evaluated for the prepared samples by using Fritzsche model. The shift in fermi level away from the conduction band edge explains observed enhancement in seebeck coefficient. The incorporated nanosheets effectively scatters phonons leading to diminished thermal conductivity and improved ZT. ZT peaks to 0.34 at 448 K for the sample BT1CN with 1 wt.% of g-C3N4.

Structural, optical, and physical properties investigations of Bi2Te3 topological insulator nanocomposites exposure to 60Co γ-rays

Bi2Te3 nano-composites were accomplished by the solvothermal method and exposed to γ-rays (60Co source). XRD investigates the structural parameters of these nanostructured materials where SEM analysis confirms the nanostructured size and proves the change of the surface topography due to the irradiation process of the samples. The ESR exhibits the influence of the spins, Δg, and the number of defects for the pre-irradiated and post-irradiated Bi2Te3 samples. The optical properties, such as energy gap, refractive index, extinction coefficient, and dielectric constants, were obtained from the diffused reflectance data in the range between 200:800 nm. The optical energy gap for the pre-irradiated Bi2Te3 sample (0.72 eV) was the lowest, while the highest allowed energy gap was recorded for Bi2Te3/100 kGy sample (1.18 eV). The optical parameters were impinged on according to the change in the physical properties owing to the irradiation processing.

Delivery of Platinum(IV) Prodrugs via Bi2Te3 Nanoparticles for Photothermal-Chemotherapy and Photothermal/Photoacoustic Imaging.

Combinational administration of photothermal therapy (PTT) and chemotherapy (CT) shows great potential in improving the efficiency of tumor treatment. Herein, we designed a novel nanocomposite Pt@Bi2Te3 composed of bismuth telluride (Bi2Te3) nanoparticles and platinum(IV) prodrugs (Pt) for PTT-CT combination therapy. The obtained Bi2Te3 was synthesized by a simple solvothermal method and modified by polyethylene glycol, which exhibited excellent photothermal (PT) efficiency and stability and could also serve as a bimodal bioimaging contrast agent in PT and photoacoustic (PA) imaging. In vitro experiment results showed that the nanocomposite Pt@Bi2Te3 could effectively increase the uptake of platinum in cancer cells, which could kill tumor cells through the combined effect of PTT and CT. Furthermore, combination therapy of cancer in vivo was achieved with obvious tumor-growth inhibition without inducing observed side effects. We revealed the great potential of Bi2Te3 nanocomposites in increasing therapeutic efficiency by PTT-CT therapy and PA-PT imaging.

High Performance Thermoelectric Films with Nanoengineered Electrochemical Process for Micro Thermoelectric Power Generators

Novel electrochemical processes of Bi2Te3 nanocomposites been developed for micro thermoelectric power generators (micro TEG) with a high figure of merit (ZT) at room temperature. Nanoparticles or/and carbon nanomatrials are dispersed in an electrolyte for electrodeposition, and co-electrodeposition is performed to make a thin or thick film. The small grained nanocomposite film is formed by the inclusion of the nanoparticles or/and carbon nanomaterials. Reduction of thermoelectric properties can be observed because of the phonon scattering with the nanostructures. In addition, nanomaterials inclusion can change the carrier density of the composite films, thus, appropriate density of inclusion can improve the performances of the electrical conductance and Seebeck coefficient. Maximum ZT ~1 is obtained by optimization of the deposition condition, which is 6 times higher than that of reported pristine Bi2Te3 deposited by electrodeposition also higher value than that of bulk Bi2Te3 (0.7~0.8). Those results show that this deposition methods have a high potential ability to manufacture the micro TEG for energy harvesting devices. Figure 1

Enhanced TE properties of Cu@Ag/Bi2Te3 nanocomposites by decoupling electrical and thermal properties

Cu@Ag/Bi2Te3 nanocomposites were prepared for the first time by ultrasonic dispersion-rapid freeze-drying method combined with spark plasma sintering (SPS). By changing the content of Cu@Ag nanoparticle, we could modulate the temperature dependent thermoelectric properties. The highest ZT value can be obtained at 450 K for 1 vol% Cu@Ag/Bi2Te3, which is benefited from the decoupling of electrical and thermal properties. With the increase of electrical conductivity, the absolute value of Seebeck coefficient lifts while the thermal conductivity declines. Meanwhile, the average ZT value between 300 K and 475 K was 0.61 for 1 vol% Cu@Ag/Bi2Te3, which is much higher than that of pristine Bi2Te3. Therefore, the decoupling effect of Cu@Ag nanoparticles incorporation could be a promising method to broaden the application of Bi2Te3 based thermoelectric materials.

Simple approach to synthesize CNTs uniformly coated Bi2Te3 nanocomposites by mechanical alloying

One-dimensional nanocomposite containing multiwall carbon nanotubes (MWCNTs) and thin bismuth tellurite (Bi2Te3) nanotubes have been synthesized using ball-milling process. The primary focus of this work is to study the morphological, molecular bonding, and structure of the novel nanocomposite and to explore the underlying mechanism to synthesize a novel nanocomposite for thermoelectric applications. The experimental results from the high-resolution TEM revealed that MWCNTs are uniformly coated on the surface of the Bi2Te3 nanotubes consisting of a bundle of two. Furthermore, it indicated that minimal strain is present at the interface between MWCNTs and Bi2Te3 nanotubes which can add additional lattice scattering, and hence, the lattice contribution to the thermal conductivity can be further reduced due to phonon-blocking phenomena. Analytical analysis results further indicated that the MWCNTs incorporated in the nanocomposites showed less disorder and successfully formation of the nanocomposites. We believe that our approach provides the advantages of simplicity, efficient and opens a new way to prepare a novel 1D thermoelectric nanocomposite which can further improve the thermophysical properties for future energy-harvesting applications and thermoelectric devices.

A simple energy-saving aqueous synthesis of Bi2Te3 nanocomposites yielding relatively high thermoelectric power factors

We discover a simple scalable (10 g scale for one batch in this study) route of synthesizing Bi2Te3 nanocomposites in aqueous solution with high yield at room temperature without involving any organic chemicals, capping agents, and surfactants. It is conceivable that the formation mechanism involves interaction between elemental Bi and Te, which takes place at a very slow rate and takes about 2 weeks to form Bi2Te3. Heat treatment of Bi2Te3 nanocomposite yields a single phase of Bi2Te3 with the relatively high power factor of 24.2 μW/cm∙K2 at 425 K compared to other solution methods.

Thermoelectric properties of solution-synthesized n-type Bi2Te3 nanocomposites modulated by Se: An experimental and theoretical study

We report the investigation of the thermoelectric properties of large-scale solution-synthesized Bi2Te3 nanocomposites prepared from nanowires hotpressed into bulk pellets. A third element, Se, is introduced to tune the carrier concentration of the nanocomposites. Due to the Se doping, the thermoelectric figure of merit (ZT) of the nanocomposites is significantly enhanced due to the increased power factor and reduced thermal conductivity. We also find that thermal transport in our hot-pressed pellets is anisotropic, which results in different thermal conductivities along the in-plane and cross-plane directions. Theoretical calculations for both electronic and thermal transport are carried out to establish fundamental understanding of the material system and provide directions for further ZT optimization with adjustments to carrier concentration and mobility.

Bismuth telluride nanostructures: preparation, thermoelectric properties and topological insulating effect

Bismuth telluride is known to wield unique properties for a wide range of device applications. However, as devices migrate to the nanometer scale, significant amount of studies are being conducted to keep up with the rapidly growing nanotechnological field. Bi2Te3 possesses distinctive properties at the nanometer level from its bulk material. Therefore, varying synthesis and characterization techniques are being employed for the realization of various Bi2Te3 nanostructures in the past years. A considerable number of these works have aimed at improving the thermoelectric (TE) figure-of-merit (ZT) of the Bi2Te3 nanostructures and drawing from their topological insulating properties. This paper reviews the various Bi2Te3 and Bi2Te3-based nanostructures realized via theoretical and experimental procedures. The study probes the preparation techniques, TE properties and the topological insulating effects of 0D, 1D, 2D and Bi2Te3 nanocomposites. With several applications as a topological insulator (TI), the topological insulating effect of the Bi2Te3 is reviewed in detail with the time reversal symmetry (TRS) and surface state spins which characterize TIs. Schematics and preparation methods for the various nanostructural dimensions are accordingly categorized.

Preparation of 1-D/3-D structured AgNWs/Bi2Te3 nanocomposites with enhanced thermoelectric properties

A novel and facile approach is demonstrated to dramatically enhance thermoelectric properties by means of introducing one-dimensional (1-D) silver nanowires (AgNWs) into a three-dimensional (3-D) Bi2Te3 matrix in order to construct 1-D/3-D structured nanocomposites. The influence of different concentrations of AgNWs on the morphology and thermoelectric properties of Bi2Te3 is investigated in detail. The results show that the dispersed AgNWs effectively suppress grain growth and form new interfaces with the Bi2Te3 matrix. In contrast to pure bulk Bi2Te3, almost all bulk samples dispersed with AgNWs exhibit the much lower thermal conductivity and higher power factors. Consequently, the maximum ZT of the AgNW-dispersed Bi2Te3 nanocomposites is amazingly found to be 343% higher than that of the pure Bi2Te3. These results demonstrated that the dispersion of AgNWs could form new interfaces with the matrix and introduce defects to cause strong scattering of long-wavelength phonons, and therefore significantly reduce the lattice thermal conductivity. Our study confirms that introducing 1-D nanodispersoids into a 3-D thermoelectric matrix is promising approach to improving ZT values significantly.

High performance Bi2Te3 nanocomposites prepared by single-element-melt-spinning spark-plasma sintering

The last decade has witnessed nanocomposites becoming a new paradigm in the field of thermoelectric (TE) research. At its core is to prepare high performance TE nanocomposites, both p- and n-type, in a time and energy efficient way. To this end, we in this article summarize our recent effort and results on both p- and n-type Bi2Te3-based nanocomposites prepared by a unique single-element-melt-spinning spark-plasma sintering procedure. The results of transport measurements, scanning and transmission electronic microscopy, and small angle neutron scattering have proved essential in order to establish the correlation between the nanostructures and the TE performance of the materials. Interestingly, we find that in situ formed nanocrystals with coherent boundaries are the key nanostructures responsible for the significantly improved TE performance of p-type Bi2Te3 nanocomposites whereas similar nanostructures turn out to be less effective for n-type Bi2Te3 nanocomposites. We also discuss the alternative strategies to further improve the TE performance of n-type Bi2Te3 materials via nanostructuring processes.

Thermopower enhancement in conducting polymer nanocomposites via carrier energy scattering at the organic–inorganic semiconductor interface

The energy-filtering effect was successfully employed at the organic–inorganic semiconductor interface of poly(3-hexylthiophene) (P3HT) nanocomposites with the addition of Bi2Te3 nanowires, where low-energy carriers were strongly scattered by the appropriately engineered potential barrier of the P3HT–Bi2Te3 interface. The resulting P3HT–Bi2Te3 nanocomposites exhibited a high power factor of 13.6 μW K−2 m−1 compared to that of 3.9 μW K−2 m−1 in P3HT. The transport characteristics of nanocomposites, including the carrier concentration, mobility, and energy-dependent scattering parameter, were revealed by the experimental measurements of electrical conductivity, Seebeck coefficient, and Hall coefficient to quantitatively elucidate the carrier energy scattering at the P3HT–Bi2Te3 interface. The ability to rationally engineer the organic–inorganic semiconductor interfaces of polymer nanocomposites to achieve an improved Seebeck coefficient and power factor provides a potential route to high-performance, large-area, and flexible polymer thermoelectric materials.

Influence of Nanoinclusions on Thermoelectric Properties of n-Type Bi2Te3 Nanocomposites

n-Type Bi2Te3 nanocomposites with enhanced figure of merit, ZT, were fabricated by a simple, high-throughput method of mixing nanostructured Bi2Te3 particles obtained through melt spinning with micron-sized particles. Moderately high power factors were retained, while the thermal conductivity of the nanocomposites was found to decrease with increasing weight percent of nanoinclusions. The peak ZT values for all the nanocomposites were above 1.1, and the maximum shifted to higher temperature with increasing amount of nanoinclusions. A maximum ZT of 1.18 at 42°C was obtained for the 10 wt.% nanocomposite, which is a 43% increase over the bulk sample at the same temperature. This is the highest ZT reported for n-type Bi2Te3 binary material, and higher ZT values are expected if state-of-the-art Bi2Te3−x Se x materials are used.

Effect of Nanopowders Addition on the Thermoelectric Properties of n-Type Bi2Te3 Nanocomposites

Bi2Te3 nanopowders with an average grain size of about 40 nm were synthesized by vacuum arc plasma evaporation. The n-type bulk Bi2Te3 nanocomposites were prepared by consolidating the mixtures of these nanopowders and mechanically alloyed powders using plasma activated sintering, and the effect of the addition of nanopowders on the thermoelectric properties of bulk Bi2Te3 nanocomposites was investigated. With increasing the content of the added nanopowders, the electrical resistivity and Seebeck coefficient of the nanocomposites increased and the thermal conductivity decreased. When the content of the added nanopowders was 20 wt%, the thermal conductivity decreased by 21.4% compared with that of the nanopowders-free compounds. A preliminary investigation showed that the addition of nanopowders was an effective way to decrease the thermal conductivity and increase the thermoelectric efficiency.

Thermoelectric and transport properties of n-type Bi2Te3 nanocomposites

A series of Bi2Te3 nanocomposite samples have been prepared by incorporating nanoparticle concentrations of 5–50mol% into a bulk matrix via a mixing process and subsequently hot pressing into highly densified pellets. The electrical resistivity, thermopower, total thermal conductivity, carrier concentration, and Hall mobility have been measured for these composites, and the power factor, lattice thermal conductivity, and figure of merit (ZT) have been calculated. The results are discussed in light of the underlying electrical and thermal transport mechanisms.

Synthesis and transport properties of Bi2Te3 nanocomposites

Nanostructured Bi2Te3 compounds have been synthesized by a circulating reflux method. The morphologies of the nanopowders are mainly related to the surfactants and reactants used in the syntheses. Bi2Te3 nanocomposites were obtained by hot-pressing the mixture of nano and micro-powders of Bi2Te3 in different ratios. It is found that the electrical transport properties of the nanocomposites are different from conventional Bi2Te3 alloys. Electrical conductivity increased while the Seebeck coefficient changed from positive to negative with increasing temperature.