The process of electrochemical intercalation and deintercalation of copper ions into Bi2Te3 single crystals was studied and a conception of embedding of copper ions into octahedral and tetrahedral sites of the van der Waals gaps was proposed. Taking the lattice-gas model into consideration, values of octahedral and tetrahedral site energies, E-1 = - 0.07 eV and E-2 = - 0.31 eV, were determined. It was found that intercalated copper ions behave either as donors located in the van der Waals gaps and interstitial sites of five-plane layers of the crystal or as inactive species. To enlighten this effect, a model assuming an interaction of Cu+ ions with Te-1 atomic planes and the formation of uncharged four-layer lamellae (Cu-Te-Bi-Te) and seven-layer lamellae carrying delocalised negative charge (Bi3Te4)- was proposed. (C) 2004 Elsevier B.V. All rights reserved.