Bismuth telluride (BixTey) nanowires were electrodeposited from aqueous acidic solutions containing different Bi3+/HTeO2+ (20/20 and 20/10 mM) concentration ratios. The polarization plots predicted that combined solutions exhibit more noble reduction potentials than individual solutions. Optimized deposition potentials were obtained from the combined electrolyte polarization plots. An anomalous codeposition behavior caused an increase in Te concentration for depositions in the kinetic region of bismuth telluride; otherwise, decreasing Te concentrations with increased deposition potentials was observed from a composition analysis. X-ray diffraction showed a dominant (110) orientation for nanowires at low deposition potentials. n-Type nanowires were obtained from both electrolytes, while p-type nanowires were only obtained from the 20/10 electrolyte for low Te (<30%) concentrations. An intrinsic to extrinsic transition was observed for nanowires deposited from the 20/10 electrolyte. The highest measured Seebeck coefficient was −318.7 and 117μV/K for n- and p-type nanowires, respectively. The Seebeck coefficient dependence on the resistivity and composition of the nanowires is discussed.
Bismuth antimony telluride ͑BiSbTe͒ nanowires were electrodeposited at constant potentials into polycarbonate templates from a tartaric-nitric acid electrolyte. Optimum deposition potentials were obtained from polarization and compositional analysis. X-ray diffraction analysis showed a preferential ͑015͒ orientation for the nanowires. The Bi 2 Sb 0.6 Te 3 nanowire sample deposited at Ϫ150 mV showed a high Seebeck coefficient ͑S͒ of −630 V/K.Concerns over the depleting fossil fuels and increasing global warming threat stimulated the researchers to develop efficient thermoelectric materials, defined by the figure of merit as ZT = S 2 T/k, where S is the Seebeck coefficient, is electrical conductivity, T is the absolute temperature, and k is thermal conductivity. 1 The ZT of the current bulk materials is limited to 1; 2 however, a value higher than 3 is required to compete with conventional energy techniques. Increasing the thermoelectric power factor ͑S 2 ͒ and decreasing the thermal conductivity are the two main approaches to increase ZT. In superlattice Bi 2 Te 3 /Sb 2 Te 3 thin films, a high ZT of 2.4 was obtained mainly by the decreased lattice thermal conductivity. 3 Taking into account the improved density of states resulting in higher power factors and decreased phonon thermal conductivity due to surface scattering, Dresselhaus's group 2,4 predicted an even higher ZT for one-dimensional nanostructures. Also, experimental results showed 5 that BiTe nanowires have lower thermal conductivity than their bulk counterparts.Stacy's group 6 was the first to report electrodeposition of BiSbTe nanowires in porous alumina templates using a tartaric-nitric acid based electrolyte and proposed different mechanisms for the reduction of BiSbTe alloys following the overall reaction Del Frari et al. 7,8 studied the optimum conditions for electrodeposition of Bi 0.5 Sb 1.5 Te 3 alloys from a tartaric-perchloric acid bath and measured a thin-film power factor of 600 WK −2 m −1 . Xiao et al. 9 electrodeposited ͑Bi 0.3 Sb 0.7 ͒ 2 Te 3 and Bi 1.8 Sb 0.1 Te 3.1 nanowires in polycarbonate template and described their semiconducting nature from the temperature-dependent current-voltage plots. Although few articles are available on the electrodeposition of BiSbTe nanowires, 6-9 there is a need for their thermoelectric characterization. Our current research focuses on achieving higher Seebeck coefficients, by optimizing the alloy composition, using electrodeposited of BiSbTe nanostructures. To the best of our knowledge, the reported Seebeck coefficients here are the highest values among the electrodeposited BiTe alloy family ͑BiSbTe and BiSeTe͒ materials. 10-12 ExperimentalBiSbTe nanowires were electrodeposited into polycarbonate membranes using a Solartron 1287 function generator at constant potentials and room temperature from a tartaric-nitric acid based electrolyte. Being difficult to dissolve, Sb 2 O 3 was treated with tartaric acid as a complexing agent to increase its solubility in water, and the obtained solution was mixed with...
A novel conceptual mechanism for cooling Giant magneto resistance (GMR) nanostructures using bismuth telluride (BixTey) thermoelectric caps is reported for first time. BixTey thin films and nanowires were electrodeposited from an aqueous electrolyte solution using a constant potential method. GMR layered structures were electrodeposited form a Co-rich electrolyte using a pulsed potential technique. Optimal deposition potentials were identified from polarization analysis. Thin film morphology was found to be strongly dependent on deposition potentials. With increased deposition potentials crystalline to polycrystalline transition and decreased Te concentration were observed from XRD and EDS analysis, respectively. A maximum Seebeck coefficient of -200μV/K was obtained at 345K for a thin film sample deposited at -150mV.
Bismuth antimony telluride (BiSbTe) nanowires were electrodeposited at constant potentials into polycarbonate templates from a tartaric-nitric acid baths having different electrolyte compositions. Composition analysis of the nanowires showed that Sb deposits at higher potentials compared to BiTe. Maximum seebeck coefficients of -337.7 μV/K and 227.2 μV/K were obtained for n-type and p-type nanowires samples Bi4.6Te5.4 and Bi4.3Sb5 respectively. Nonmonotonic resistance behavior was observed for all the nanowires.
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