Ga. Torchia et al., COMPOSITIONAL EFFECT ON CR3-CR CONGRUENT AND STOICHIOMETRIC CRYSTALS(SITE DISTRIBUTION IN MGO OR ZNO CODOPED LINBO3), Journal of physics. Condensed matter, 10(21), 1998, pp. 341-345
In this letter optical and electron paramagnetic resonance (EPR) techn
iques are used to investigate the effect of stoichiometry changes on t
he site distribution of Cr3+ ions in LiNbO3:Cr crystals with (or witho
ut) MgO or ZnO codoping. In congruent (Li0.95Nb1.01O3) crystals codope
d with MgO (ZnO) the Cr3+ ions begin to enter into the Nb5+ site for c
oncentrations higher than 4.5% (4.7%). Below this MgO (ZnO) threshold
Cr3+ ions enter only into the Li+ sites. However, for nominally stoich
iometric (LiNbO3) crystals, the threshold concentration is much lower
(between O and 0.2% in our crystals). The use of Cr3+ ions as an optic
al and paramagnetic probe to evaluate the grade of stoichiometry is co
nsidered.