LAGUTA, V. V., GLINCHUK, M. D., BYKOV, I. P., MAKSIMENKO, J. L., ROSA, J., JASTRABÍK, L. Impurity centers in PbTiO3 single crystals: An electron-spin-resonance analysis. Physical Review B. 1996, 54(17), 12353-12361. ISSN 0163-1829.