Electrodeposition of stoichiometric bismuth telluride Bi2Te3 using a piperidinium ionic liquid binary mixture

In this paper, we report the electrodeposition of stoichiometric Bi2Te3 compound using an ionic liquid binary mixture: 1-ethyl-1-octyl-piperidinium bis(trifluoromethylsulfonyl)imide: 1-ethyl-1-octyl-piperidinium bromide (EOPipTFSI:EOPipBr 95:5 (mol%)). The use of this mixture allows to reach a higher solubility of Bi(III) and Te(IV) precursors compared to pure EOPipTFSI ionic liquid in which Te(IV) salts are not soluble. Moreover, this electrolyte presents an extended cathodic stability, allowing the study of electrochemical processes that occur at high cathodic potential values. A detailed voltammetric study of electrochemical systems was performed for electrolytes containing different [Bi(III)]/[Te(IV)] ratio, allowing the attribution of cathodic signals to electrochemical processes. Experimental conditions leading to the deposition of stoichiometric Bi2Te3 were then determined by varying deposition potential and electrolyte composition, using potentiostatic experiments followed by XRD and SEM-EDX analysis. By varying the concentration of precursors in the electrolyte, mirror-like coatings, adherent and homogeneous, were obtained. Electroplated Bi2Te3 presents n-type conductivity with a Seebeck coefficient equal to −70 μV K−1 and an electrical resistivity of 133 μΩ m.