An axial electron paramagnetic resonance signal which had been observed in vacuum-annealed single crystals, doped with 8mol%Mg and 0.05mol%Ti, was attributed to Ti3+ on Nb sites. The g-tensor components (g|| = 1.760, g = 1.786 at 5K; g|| = g = 1.893 at 74K) resulted in very low values of the orbital reduction factor and could be explained in terms of a dynamic pseudo Jahn-Teller effect. The vibronic coupling of the center was much stronger than that reported for other nd1 centers with similar trigonally distorted octahedral coordination, such as Ti3+ on Li sites and trapped Nb4+ polarons on both cation sites. A stronger coupling for ions that were on, or near, the Nb site was understood as being a result of a smaller trigonal splitting of the ground state due to the more central position of the Nb site in the O octahedron. Electron transfer from the Ti3+ center to lattice Nb atoms, resulting in Nb4+ trapped polarons, was stimulated by illumination in the near-ultraviolet region. The average energy difference of the Ti4+/3+ and Nb5+/4+ donor levels was estimated to be 0.070eV; depending upon the distance of compensating Mg2+ ions on nearby Li sites.

Ti3+ on Nb Site: a Paramagnetic Jahn-Teller Center in Vacuum-Reduced LiNbO3:Mg:Ti Single Crystals. G.Corradi, I.M.Zaritskii, A.Hofstaetter, K.Polgár, L.G.Rakitina: Physical Review B, 1998, 58[13], 8329-37