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This article demonstrates a method to fabricate VO2 powder by annealing a precursor that was obtained by electrochemical intercalation of lithium into layered structured V2 O5. The method includes three steps. First, Li+ was intercalated into interlayers of V2 O5 through an electrochemical process with precisely controlled electrical discharging currents and intercalation amounts, and at the same time V5+ would be deoxidized into V4+. Secondly, the Li+-intercalated powder was rinsed in an acid solution to achieve an ion exchanging process of replacing the Li+ in the V-O frame with H+. Thirdly, the powder was annealed at 800°C in N2 atmosphere for dehydration and VO2 crystallization. By DSC investigation, the as-produced final product has a strong endothermic peak at around 68°C in a heating semicycle, which is indicative of the phase transition from VO2( M) to VO2( R). This approach can be extended to the fabrication of other sub-valence oxides by lithium intercalation and deoxidization of its higher valence layer-structured precursors. [ABSTRACT FROM AUTHOR]

Lithium intercalation and de-intercalation processes have been used to fabricate bulk Bi2Se0.3Te2.7with internal nanostructures. The doped Li content can be precisely controlled through this method. It provides a chance to directly optimize electrical properties when preparing nano-structured materials, leading to the optimum carrier concentration for improved thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]

Abstract: Reversible electrochemical lithium intercalation/deintercalation reactions have been applied to integrally modify the thermoelectric performance of Bi2Se0.3Te2.7 compounds. The carrier concentration of Bi2Se0.3Te2.7 has been precisely controlled experimentally through the adjustment of the residual lithium content. The variations of electronic transport properties of Li x Bi2Se0.3Te2.7, including electrical conductivity, Seebeck coefficient and carrier concentration, as a function of the intercalated lithium amount (x), show a special non-monotonic P-type to N-type doping trend. This variation is caused by the competition of two mechanisms controlling the carrier concentration: (i) decreasing of the Se/Te ratio through a Li–Se reaction that reduces the amount of the TeBi or SeBi antisite defects and therefore the electron concentration; (ii) n-type doping by lithium that provides the electron. Moreover, the nanoparticle exfoliation during lithium intercalation and deintercalation reactions leads to the formation of an internal nanocrystalline composite structure which effectively reduces the lattice thermal conductivity. Through an integral modification of both electrical and thermal transport properties, the maximum ZT value of Li x Bi2Se0.3Te2.7 was improved by nearly 25%. [Copyright &y& Elsevier]