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A convenient top-down method for preparation of Bi2Se0.3Te2.7crystalline nano-particles has been demonstrated. It contains two steps: (1) lithium was intercalated between the van der Waals bonded quintuple-layers by electrochemical process inside lithium ion batteries with precisely controlled speed and amount; (2) subsequent alcohol exposure of LixBi2Se0.3Te2.7to make the intercalated Li atoms explode like atom-scaled bombs and exfoliate the original micro/macro scaled materials into nano-scaled single crystalline particles with sizes around 10 nm. The intercalation process does not cost external energy, and can be scaled up by amplification of the intercalation devices. [ABSTRACT FROM AUTHOR]

Lithium intercalation and de-intercalation processes have been used to fabricate bulk Bi2Se0.3Te2.7with internal nanostructures. The doped Li content can be precisely controlled through this method. It provides a chance to directly optimize electrical properties when preparing nano-structured materials, leading to the optimum carrier concentration for improved thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]

The 1/2{h00} and 1/2{hk0} type superlattice reflections in the electron diffraction patterns indicate the presence of ordered polar regions in SrBi1.6Nd0.4Nb2O9. The research of x-ray Rietveld refinement and synchrotron radiation x-ray absorption fine structure spectroscopy determined that Nd3+ replaced Bi3+ in the Bi2O2 layers for SrBi1.6Nd0.4Nb2O9 and the relaxor behavior could be attributed to the disorder of Nd3+ and Bi3+ in the Bi2O2 layers. The tilting angle of NbO6 is obtained by Rietveld refinement method and the refinement result indicates that the substitution of Nd3+ for Bi3+ remarkably decrease the structural distortion, which leads to the lower transition temperature. [ABSTRACT FROM AUTHOR]

The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. These results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization. [ABSTRACT FROM AUTHOR]

Etching characteristics of p-type (BiSb) 2 Te 3 films were studied with CH 4 /H 2 /Ar gas mixture using an inductively coupled plasma (ICP)-reactive ion etching (RIE) system. The effects of gas mixing ratio, working pressure and gas flow rate on the etch rate and the surface morphology were investigated. The vertical etched profile with the etch rate of 600 nm/min was achieved at the optimized processing parameters. X-ray photoelectron spectroscopy (XPS) analysis revealed the non-uniform etching of (BiSb) 2 Te 3 films due to disparate volatility of the etching products. Micro-masking effects caused by polymer deposition and Bi-rich residues resulted in roughly etched surfaces. Smooth surfaces can be obtained by optimizing the CH 4 /H 2 /Ar mixing ratio. [ABSTRACT FROM AUTHOR]

Abstract: Bi2Te3 nanosheets and nanotubes have been prepared via a microwave-assisted method using ethylene glycol as solvent and reducing agent at 180°C, 190°C and 195°C. X-ray diffraction, transmission electron microscopy, electron diffraction, X-ray energy dispersive spectrometry and high-resolution transmission electron microscopy were employed to characterize the products. It is found that both the nanosheets and nanotubes are well-crystallized single crystals and morphologies of the products are greatly affected by the reaction temperature. A possible formation mechanism related to layer structure rolling was also proposed. [Copyright &y& Elsevier]

In this paper we develop scanning thermoelectric microscopy (STeM) on the basis of commercial atomic force microscope. The nanoscale thermoelectric behaviors of (Bi,Sb) 2 Te 3 (BST) thin films were studied. 3 ω -technique was used for thermal conductivity imaging and quantitative thermal characterization. By acquiring the unique Seebeck information from 2 ω frequency component, nanoscale thermoelectric images were firstly obtained, exhibiting remarkably inhomogeneous distribution of local Seebeck coefficient in the thin films. Positive thermoelectric response is revealed by the modulation of temperature difference between thermal tip and sample, corresponding to p-type conduction within BST sample. [ABSTRACT FROM AUTHOR]

Abstract: Reversible electrochemical lithium intercalation/deintercalation reactions have been applied to integrally modify the thermoelectric performance of Bi2Se0.3Te2.7 compounds. The carrier concentration of Bi2Se0.3Te2.7 has been precisely controlled experimentally through the adjustment of the residual lithium content. The variations of electronic transport properties of Li x Bi2Se0.3Te2.7, including electrical conductivity, Seebeck coefficient and carrier concentration, as a function of the intercalated lithium amount (x), show a special non-monotonic P-type to N-type doping trend. This variation is caused by the competition of two mechanisms controlling the carrier concentration: (i) decreasing of the Se/Te ratio through a Li–Se reaction that reduces the amount of the TeBi or SeBi antisite defects and therefore the electron concentration; (ii) n-type doping by lithium that provides the electron. Moreover, the nanoparticle exfoliation during lithium intercalation and deintercalation reactions leads to the formation of an internal nanocrystalline composite structure which effectively reduces the lattice thermal conductivity. Through an integral modification of both electrical and thermal transport properties, the maximum ZT value of Li x Bi2Se0.3Te2.7 was improved by nearly 25%. [Copyright &y& Elsevier]

Abstract: Highly dense n-type Bi2Te3-based thermoelectric materials dispersed with x vol.% γ-Al2O3 nanoparticles (x =0, 0.4, 1.0, 1.5) were fabricated by spark plasma sintering method. The effects of γ-Al2O3 addition on microstructure and the thermoelectric properties were studied. It was found that γ-Al2O3 nanoparticles locate both at grain boundaries and inside Bi2Se0.3Te2.7 grains. The nanoparticles induce both potential barrier scattering effect and additional phonon scattering effect, which simultaneously enhance the Seebeck coefficient and reduce the lattice thermal conductivity of the nanocomposites in the measured temperature range of 300–500K, respectively. The maximum dimensionless figure of merit (ZT max ) reaches up to 0.99 for the sample with x =1.0 at 400K, which is 35% improvement over the Bi2Te3-based matrix. More importantly, the average ZT value of the sample increases from 0.65 to 0.91 in the temperature range 300–500K, making the nanocomposites much more applicable in cooling and power generation. [Copyright &y& Elsevier]

Abstract: Highly crystallized Bi2Te3 nanosheets with typical thickness of 30nm and diameter of 250nm have been successfully synthesized using an aqueous chemical route at near room temperature. It was found out that organic ligand nitrilotriacetic acid (NTA) as well as the pH value of the precursor solution played significant roles in the formation of the sheet nanostructure. Correspondingly, a possible formation mechanism concerning the soft-template of NTA was proposed. To investigate the effect of Bi2Te3 nanostructures on phonon scattering, thermal conductivities of bulk Bi2Te3 samples with and without nanosheets were measured. The lattice thermal conductivity as low as 0.36WmK−1 was gotten for the bulk sample with embedded nanostructure, which is about one half of that for sample without nanosheets. [Copyright &y& Elsevier]

Abstract: Two crystals of Bi2Se0.21Te2.79 doped with 0.08wt% TeI4 were grown by zone melting on the Foton-M3 spacecraft of Russia and the ground in 2007, respectively. The chemical composition, structure and thermoelectric properties of the space and ground crystals grown were evaluated by EPMA, XRD and thermoelectric measurements including Seebeck coefficient, electrical conductivity and thermal conductivity. The compositions of the space crystal grown along growth direction were more homogeneous than that of the ground crystal grown. The crystallization of space crystal grown was obviously improved. The maximum ZT value of space crystal reached 1.14 at 300K, which was higher about 29% than that of ground crystal at room temperature. These results imply that the composition homogeneity and crystallization of Bi2Se0.21Te2.79 crystal can be improved under microgravity conditions, which is helpful for enhancing thermoelectric figure of merit of Bi2Te3-base materials. [Copyright &y& Elsevier]