S=1 AND S=2 EPR SIGNALS IN MODIFIED CUO AND BACUO2

EPR spectra of (i) CuO annealed in air at different temperatures up to 900 degrees C and (ii) CuO reacted with BaO in the ratio 3:2 at diffe rent temperatures up to 900 degrees C were studied. In (i), evidence f or the formation of monomers, dimers, and tetramers of copper ions was found. In (ii), in addition to those spectra obtained in (i), aggrega tes of four copper ions coupled through cyclic exchange with resultant electronic spin S = 2 and affected by the immediate barium neighbors were obtained. It is found that these copper aggregates giving the EPR signals are magnetically isolated from the main CuO cluster.