A simple method to determine the real composition of LiNbO₃ crystals

Abstract

The shift of t h o UV-absorption edge was applied to determine the real LiNbO, crystal cornposition. The accuracy of the method is about lo-* iiiole% iisiiig a siriiple comrnercia1 UV-sprctrophotometer. IiNhO, is a typical nonstoichionietric compound, the maximum of the phase diagram curve is shifted from the stoichiornetric 1,i:Nb = 1 ratio to the Kb rich direction (LRRNER et al.). A relatively wide homogeneity range, however, allows to produce crystal sections out of the congruent composition. The crystal quality as well as various physical parameters highly depend on the crystal composition. Both scientific investigations as well as the extended practical application demand controlled high crystal quality. Claim arose therefore to determine the real cr>stal composition in some cases. Chemical analysis and some physical methods were found to/be more or less suitable for this purpose.The chemical analysis presents an absolute method but generaly is not sensitive enough for any of the main components of the host material ( -10-l mol",,). Besides, the chemical processing of LiNbO, is rather complicated (POLGAR et al.).The practical physical methods are more sensitive ( -lop2 rnol(;b) though generally relative and are strongly affected by various impurities. Only some of then1 can be calibrated by sintered powder mixtures. (e. g. : Curie temperature measurement, phase matching temperature measurement.) I n addition these physical methods are rather inconvenient. Curie temperature measurement can be performed over thousand degrees centrigrade (BERGMANN et al.). The phase matching temperature of the second harmonic generation can be measured only by a precision laser optical system. The installation of this method therefore is too expensive. The measurement of the extraordinary refraction index with acceptable accuracy demands very high level of crystal processing (MIDWINTER). The influence of impurities on refractivity has been pointed out recently (BODNAR, YARUNICHEV).A remarkable shift of the intrinsic UV absorption edge was observed between the crystals grown from stoichiometric and congruent melt compositions ( FOLDVLRI et al.; RBDFIELD, BRUKE). This effect can easily be used to determine the crystal conlposition in the range from congruent to stoichiometric cases. Figure 1 shows the shape of the absorption curves of various crystal compositions after correcting for the reflected light from the surfaces. Relatively high absorbance is suggested t o take as reference point for the absorption edge analysis (abs. coeff. = 20 em-l). In this

Growth and optical damage resistance of Sc, Er Co-doped LiNbO3 crystals

“…The absorption edge position of different samples can be compared by the wavelength where the absorption coefficient is equal to a certain value. In this work we use optical absorption coefficient α = 20cm -1 as was introduced by Földvári et al [13,14]. In a LiNbO 3 crystal with the oxygen octahedron structure, the number of the Li + ions is less than that of Nb 5+ (Li/Nb=0.946).…”

Ion beam channeling and hyperfine interaction analysis for the characterization of stoichiometry and anti-site population in LiNbO3

“…This can be attributed to a significantly lower stopping power in the axial direction for the stoichiometric crystal, which is expected for channeling in a perfect lattice. The resulting higher proton energy at a given depth and the corresponding higher nuclear cross section for the 7 Li(p,α) 4 He reaction leads to an enhanced yield. Computer simulations using the CASSIS code [11] show that in the case of stoichiometric lithium niobate the (0001) angular scan can be described assuming a perfect crystal lattice, as shown in Fig.…”

Inhomogeneity of composition in near-stoichiometric LiNbO3 single crystal grown from Li rich melt

“…It is well known that the position of the fundamental absorption edge is very sensitive to the Li/Nb ratio in LiNbO 3 [16] . A pronounced blue shift will occur if the Li content has increased in the crystal [16,17].…”

“…The optical spectra were measured with a Hitachi U-3500 spectrophotometer. Eq (1) was used to determine the composition of the samples [16]:…”

“…A pronounced blue shift will occur if the Li content has increased in the crystal [16,17]. In order to characterize the axial composition homogeneity in a near-stoichiometric LiNbO 3 single crystal, two (0 0 0 1) slices were cut from the top and bottom of the boule.…”