The influence of lithium intercalation and iodine on the electrical properties of the superconductor Nd1.82Ce0.18CuOz

Abstract

As-prepared Nd 1.82 Ce 0.18 CuO z pellets treated by electrochemical lithium intercalation and iodine vapour were studied. It was found that the sample Li 0.06 Nd 1.82 Ce 0.18 CuO z intercalated by lithium at 705 °C, using LiF/KF melt electrolyte, became superconductive at T rmc =23.5 K. The mechanism is considered to be that lithium has been inserted into the interstitial site near the CuO square and has donated its electron to the CuO 2 plane, while the extra oxygen atom has been removed. The insertion of lithium using LiClO 4 polypropylene carbonate electrolyte cells at room temperature was very slow and no superconductivity was observed. For these samples with lithium inserted at room temperature and then annealed at 900 °C in air, the defect oxygen atoms can be introduced into the structure along with lithium as shown by the increase of resistivity with the lithium amount. The samples treated with iodine at 200 °C showed a resistivity drop between 9.9 and 13.9 K, which might indicate superconductivity in a small portion with possible composition Nd 1.82 Ce 0.18 CuO z−y I y . Combined with the results of the luminescence spectra, the mechanism of deoxygenation can be considered as the delocalization of the doped electrons in the crystal.