Cr 3+ centres in LiNbO 3: Experimental and theoretical investigation of spin hamiltonian parameters

Abstract

X-band EPR spectra of Cr 3+ ions in ferroelectric LiNbO 3 single crystal at room temperature are analyzed assuming Cr 3+ 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 1 3+) and (II) the weak (Cr II 3+) spectra. The axial zero-field splitting parameter for a Cr 3+ 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 Cr II 3+ at the Nb site. For Cr 3+ ion at the structural vacancy site the parameter D SV is calculated as a function of displacement of Cr 3+ ion from the centre of the oxygen octahedron along the [1 1 1] direction. Other weak and unresolve spectra also observed by us can possibly be due to Cr 3+ centres at vacancy site.