Electrochemical intercalation of lithium into layered niobates ACa₂Nb₃O₁₀ (A = K, Rb, Cs)

We prepared Li-intercalated layered niobium oxide Li_xACa₂ Nb₃O₁₀ (A = K, Rb, Cs) an electrochemical technique. The host compounds ACa₂Nb₃O₁₀ were synthesized by a solid state reaction method at 850 - 1150°C for 10 - 12h. Each of the cyclic voltammograms of these compounds had one cathodic peak at approx. -3 V, indicating that the Li-intercalation occurred at this voltage. All of the intercalated compounds Li_xACa₂Nb₃O₁₀ (A = K, Rb, Cs) showed superconductivity at 4 - 5 K, and their x-ray diffraction pattern remained almost unchanged in spite of the Li-intercalation. For Li_xRbCa₂Nb₃O₁₀, no superconductivity appeared up to x = 0.34 and 0.46 Tc (determined as the onset of the Missner effect) was constant at 4K, and for x=0.62 Tc decreased slightly to 3K.