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 LixAB2Nb3O10 (A=K, Rb, Cs, B=Ca, Sr) by an electrochemical technique. The host compounds AB2Nb3O10 were synthesized by a solid state reaction method at 850–1050 °C 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 AB2Nb3O10|1.0 M LiClO4/PC|Pt, where the working electrode was a pellet of AB2Nb3O10 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 ∼−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 LixKCa2Nb3O10. All of the samples of Li0.34AB2Nb3O10, which is obtained for only 1.5∼2.5 h of the intercalation treatment, showed superconductivity at 4–6 K.