EPR investigation of Gd3+ and Eu2+ in the α- and β-phases of lead phosphate

The X-band EPR spectra of Gd3+ and Eu2+ diluted in Pb3(PO4)2 crystals are studied. Lead phosphate exhibits a ferroelastic phase transition at 180 0C and the EPR spectra obtained in each phase differ from each other. The spectra are very complex because the zero field splitting has the same order of magnitude as the Zeeman term. The spin Hamiltonian parameters and the energy levels are computed. 'Forbidden' or 'missing' transitions and line intensities can be explained. Very likely Gd3+ substitute a Pbsub(I) ion. For Gd3+ in β-phase g approximately 2 and b20 = 990x10-4 cm-1 (200 0C); for Gd3+ in A-phase at 25 0C g approximately 2, b20 = 930x10-4 cm-1 and b22 = -77x10-4 cm-1. (author)