Effect of various deposition parameters on the co-deposition behavior of cobalt antimony in citric-based solution
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X.J. Xu Department of Engineering Materials, University of Sheffield, Sheffield S1 3JD, United Kingdom (Received 13 March 2008; accepted 4 August 2008)
Direct current (dc) electrodeposition was used to co-deposit cobalt and antimony in citric-based solutions. Growth behavior of Co–Sb alloy thin films was systematically studied under various deposition conditions. Effects of deposition parameters (i.e., deposition potential, cobalt sulfate concentration, and pH value) on the microstructure, chemical, and phase composition of the deposited materials were also studied and are discussed in detail.
I. INTRODUCTION
Thermoelectric (TE) materials are attracting renewed interest for their potential to harvest the huge amount of waste heat (∼2/3) from power plants and automobiles. The conversion efficiency of TE materials is defined by the dimensionless figure of merit ZT, ZT ⳱ T␣2/, where T is the absolute temperature, ␣ is the Seebeck coefficient, and and are the electrical and thermal conductivity, respectively. A ZT value > 3 is necessary to position thermoelectrics to be a significant contributor to our energy needs.1 However, for many decades the progress in improving the ZT of bulk TE materials is slow and far behind the need. To date, the best ZT reported in bulk TE materials is around 1–2.2 Hence, other than traditional processing techniques, new and innovative ideas and approaches are necessary to make a breakthrough in the TE conversion efficiency. Low-dimensional (thin film, nanowire array, and quantum dot) TE structures are promising solutions for high ZT. Recent theoretical calculations have suggested a significant enhancement in ZT (ZT > 3) as the dimensionality of the traditional TE materials is decreased, benefiting from both quantum confinement effects to carriers and pronounced phonon scattering at the boundaries.3,4 Much higher ZT values (2–4) have been experimentally observed in superlattice TE thin films.5,6 The great potential of developing low-dimensional TE device with nanowire materials has also been examined.7 Electrodeposition is a promising technique to produce low-dimensional structures in large scale and at a low Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2008.0361 J. Mater. Res., Vol. 23, No. 11, Nov 2008
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cost. It has been widely used in depositing various compound/alloy materials.8–11 The ability to deposit materials with high aspect ratios makes the technique suitable for developing high-density nanowire TE devices. Electrodeposition has been intensively used in depositing Bi2Te3-based thin film/nanowire thermoelectrics. There are limited reports on the electrodeposition of other TE materials, e.g., CoSb3-based skutterudites.
FIG. 1. Grazing incidence XRD results of the films deposited under various potentials in electrolyte solutions containing 0.003 M Sb(III), 0.172 M Co, 0.196 M citric acid, and 0.125 M potassium citrate (pH ⳱ 3.03). XRD pa
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