Synthesis and superconducting properties of Li-intercalated niobium oxide LixAB2Nb3O10 (A:alkaline metal, B:alkaline earth metal) by electrochemical technique

We prepared Li-intercalated layered niobium oxide Li(x)AB(2)Nb(3)O(10) (A=K, Rb, Cs, B=Ca, Sr) by an electrochemical technique. The host compounds AB(2)Nb(3)O(10) were synthesized by a solid state reaction method at 850-1050 degreesC for 10-12 h. Electrochemical intercalation of Li was carried out at room temperature under a constant potential using a potentio-galvanostat. A three-electrode cell was set up as AB(2)Nb(3)O(10)\ 1.0 M LiClO4/PC \ Pt, where the working electrode was a pellet of AB(2)Nb(3)O(10) and counter electrode was a Pt wire. LiClO4 (1.0 M) dissolved in propylene carbonate was used as an electrolyte. An Ag/AgCl electrode was used as a reference electrode connected to the LiClO4/PC solution via the salt bridge. The cyclic voltammograms of KCa2Nb3O10 had one cathodic peak at similar to -2.8 V, indicating that the Li intercalation occurred at this potential. The c-axis length decreases with increasing x, though a-axis length does not change with increasing x, in LixKCa2M3O10. All of the samples of Li(0.34)AB(2)Nb(3)O(10), which is obtained for only 1.5 - 2.5 h of the intercalation treatment, showed superconductivity at 4-6 K. (C) 2002 Elsevier Science B.V. All rights reserved.