A new method for the electrochemical deposition of Bi2+xTe3-x is presented, which combines voltage-controlled deposition pulses with current-controlled resting pulses. This method is based on results of a comprehensive electrochemical investigation including cyclic voltammetry, chronoamperometry and chronopotentiometry, which has been performed on the system Bi and Te on Pt in 2 M HNO3. The influence of electrolyte composition, deposition potential and deposition pulse duration on morphology and stoichiometry of the deposited material as well as the variation of the composition over the thickness of the layer has been investigated by means of SEM and EDX. The crystal structure was examined with XRD. Layers deposited with the new method show a constant and reproducible stoichiometry over their entire thickness. Layers of up to 800 mu m thickness deposited with deposition rates of up to 50 mu m/h have been achieved. The composition and hence the thermoelectric behavior may be adjusted via electrolyte composition or the deposition potential. Fabrication of n-type and, for the first time, p-type Bi2+xTe3-x is demonstrated and verified by measurements of the Seebeck coefficients. The suitability of the proposed method for low-cost fabrication of micro-thermoelectric devices is shown. The advantages of this method may also apply for electrochemical deposition of other binary or ternary compounds. (C) 2008 Elsevier Ltd. All rights reserved.
Modulation-free phase in heavily Pb-doped (Bi,Pb)2212 crystals
作者:N. Musolino、S. Bals、G. van Tendeloo、N. Clayton、E. Walker、R. Flükiger
DOI:10.1016/s0921-4534(03)01324-8
日期:2003.11
We report the complete disappearance of the structural modulation in heavily lead-doped Bi2-xPbxSr2CaCu2O8+delta crystals observed by transmission electron microscopy. Crystals with a nominal lead content of x = 0.8, corresponding to an effective lead content of x = 0.39, yield the non-modulated phase. The superconducting properties of this modulation-free phase (beta phase) have been studied and compared to those of undoped crystals displaying the modulated phase (alpha phase). Magnetisation measurements reveal that the irreversibility field H-irr(T) and relaxation rates are strongly improved within the beta phase. Measurements of the lower critical field, H-c1, show that the anisotropy factor, epsilon, is considerably reduced in the modulation-free crystals. This is the signature of stronger coupling between CuO2 layers which in turn deeply influences the effectiveness of the pinning. These measurements explain the enhanced pinning properties in moderately Pb-doped crystals in which the alpha phase and beta phase coexist. The enhanced pinning is not only due to the alpha/beta interfaces, which act as effective pinning centers: the emergence of modulation-free domains, characterized by a strongly reduced anisotropy, also significantly contribute to this effect. (C) 2003 Elsevier B.V. All rights reserved.
Transport critical currents in Bi Sr Ca Cu O pellets and single crystals.
作者:A. De Ninno、P. Gislon、M. Marinelli、G. Paterno'、U. Gambardella、P. Paroli、G. Balestrino
DOI:10.1016/0921-4534(89)91054-x
日期:1989.12
Preparation of the 110 K high Tc superconductor Bi2Sr2Ca2Cu3Oy by Pb and Sb substitution