CR3+ CENTERS IN LINBO3 - EXPERIMENTAL AND THEORETICAL INVESTIGATION OF SPIN-HAMILTONIAN PARAMETERS

X-band EPR spectra of Cr3+ ions in ferroelectric LiNbO3 single crystal at room temperature are analyzed assuming Cr3+ enters either of the three possible sites: Li, Nb and structural vacancy (SV) site. The observed spectra can be resolved into (I) the main (Cr(l)3+ and (II) the weak (Cr(II)3+) spectra. The axial zero-field splitting parameter for a Cr3+ centre at Li site (D(Li)) as well as Nb site (D(Nb)) is calculated using the superposition model. The values D(Li) and D(Nb) agree well with the experimental D value for Cr(I)3+ and Cr(II)3+, respectively. This confirms that the main spectra can be attributed to Cr(I)3+ at the Li site and the weak spectra to Cr3+ at the Nb site. For Cr3+ ion at the structural vacancy site the parameter D(SV) is calculated as a function of displacement of Cr3+ ion from the centre of the oxygen octahedron along the [111] direction. Other weak and unresolved spectra also observed by us can possibly be due to Cr3+ centres at vacancy site.