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.