Electron paramagnetic resonance of exchange-coupled pairs of C2+ ions was observed in KTaO3:Cu, K1-xLixTaO3:Cu and K1-xLixTa1-yNbyO3:Cu single crystals. The spectra were typical of centers with S = 1 and tetragonal symmetry with the pair axis parallel to the [100], [010] or [001] directions. The angular and temperature dependences of the signals were studied. The experimental results were explained in terms of a pair center model, which consisted of a chain of 2 equivalent Cu ions and three O vacancies. The two Cu ions occupy neighbouring Ta sites and one of the O vacancies lies between them, the chain running in the <100> direction. Ferromagnetic exchange coupling took place between the Cu ions, as confirmed by the thermal behaviour of the corresponding electron paramagnetic resonance spectra.

Electron Paramagnetic Resonance of Copper Centres in Potassium Tantalate Single Crystals. A.G.Badalyan, P.G.Baranov, D.V.Azamat, V.A.Trepakov, C.B.Azzoni, P.Galinetto, M.C.Mozzati, L.Jastrabik, J.Rosa: Journal of Physics - Condensed Matter, 2002, 14[27], 6855-63