Electrochemical intercalation of lithium in layered niobates AB₂Nb₃O₁₀ (A = K, Rb, Cs; B = Ca, Sr) and their superconductivity

We have succeeded in preparing Li-intercalated layered niobium oxide Li_xAB₂Nb₃O₁₀ (A = K, Rb, Cs; B = Ca, Sr) by an electrochemical technique. The host compounds AB₂Nb₃O₁₀ were synthesized by a solid state reaction method at 850-1150°C for 10-12 h. All of the intercalated compounds showed superconductivity at 4-6 K. In the cases of A = Rb, B = Ca, and A = Cs, B = Ca, no superconductivity appeared up to x = 0.17; for x = 0.34 and 0.46 T_c was constant with maximum value, and for x = 0.62 T_c decreased slightly. On the other hand, the correlation between T_c (onset) and a-axis length demonstrates that T_c tends to increase with a-axis length increasing, which was found in Li_0.34 AB₂Nb₃O₁₀ with optimum Li content.