Electrical properties of Cu-O monolayers intercalated into crystalline graphite

Electrical properties of Cu-O monolayers intercalated into crystalline graphite have been studied at microwave frequencies (up to 1 GHz) in the temperature range 80–400 K. As the temperature increases above 300 K, the resistance of the starting graphite samples increases because of oxygen desorption. Heating a sample containing intercalated Cu-O layers results in a transition from the metallic to the semiconducting (or insulating) state in the 95–130 K interval. At T=8 K, the samples exhibit microwave absorption typical of superconductors (this effect is not observed at T=260 K).