Evidence of a phase transition in Cu-O chains of LiCuO2

The temperature dependence of the de resistance of LiCuO2, a material having parallel one dimensional CuO2 chains, indicates semiconducting behavior with a transition to a smaller band gap occurring in the vicinity of 180 K. At approximately the same temperature there is an onset of a change of the g values and line width of the electron paramagnetic resonance spectrum of Cu2+ as well as an abrupt change in the Curie-Weiss dependence of the susceptibility suggesting the possibility of a structural change and/or a charge ordering transition in the CuO2 chains and possibly the onset of antiferromagnetic fluctuations. Also observed in the same temperature range is a pronounced drop in the surface resistance at 9.2 GHz followed by an increase which is suggested to be a result of superconducting fluctuations followed by a metal-insulator transition occurring in the surface regions of the sample of the order of the microwave penetration depth. The implications of these results with respect to similar results observed in Sr14-xCaxCu24O41, which has both CuO2 edge shared chains and Cu2O3 ladders is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.