Pulse electrodeposited bismuth-tellurium superlattices with controllable bismuth content

Abstract

Superlattice structures of (Bi2)m(Bi2Te3)n series with controllable Bi mole fraction from 0.41 to 0.71 are electrodeposited in pulse potentiostatic mode from acidic electrolytes containing Bi(NO3)3 and TeO2 as precursors. Two valence states of bismuth in superlattices are identified by X-ray photoelectron spectroscopy (XPS). One of those states is attributed to interlayered Bi0 which is present in (Bi2)m(Bi2Te3)n superlattice in the form of biatomic layers between bismuth telluride quintuples. X-ray difraction (XRD) analysis and density functional theory (DFT) calculations indicate an increase in subcell parameter asub and decrease in subcell parameter csub with the increase of Bi mole fraction. Biatomic layers of Bi0 are identified with cyclic voltammetry by characteristic anodic peak between potentials of metallic bismuth and Bi2Te3 oxidation. The selective oxidation of Bi-bilayers in (Bi2)m(Bi2Te3)n superlattice at the potential of the anodic peak results in the product corresponding to Bi2Te3 by stoichiometry, but having an expanded crystal structure. Superlattices with controllable Bi mole fraction and Bi2Te3 with “memory effect” may be of interest for design of new thermoelectric materials with controllable parameters.