EXAFS evidence for a primary ZnLidopant in LiNbO3

Abstract

We present extended x-ray-absorption fine structure (EXAFS) data as a function of temperature (10-300 K) at the Zn and Nb K edges for Zn-doped LiNbO 3. The focus is on higher Zn concentrations (7-11 mol %) for which there is disagreement in the literature as to the substitution site for Zn. Our data show that Zn substitutes only on the Li site; we find no evidence for Zn on the Nb site. However, uncertainties result in an upper bound of at most 5% of the Zn dopants being Zn Nb. In addition, the Zn Li defect produces a significant distortion in the lattice out to at least 4Å; the O atoms are attracted toward Zn while the Nb neighbors are repulsed. The Nb EXAFS agree well with the structure from diffraction for the main Nb-X peaks out to about 3.7Å. However, there appears to be a weak third Nb-O peak in the first O shell, which has a low amplitude and a longer bond length. For Nb, the shortest Nb-O bond is extremely stiff (correlated Debye temperature, θ cD ∼ 1100 K), while the longer Nb-O bond is a little weaker (θ cD ∼ 725 K) and of comparable strength to the shortest Zn-O bond (θ cD ∼ 600 K); consequently, substituting Zn at the Li site will stiffen the structure as the Li-O bonds are weak. We discuss implications of a dominant Zn Li defect.

Resolution of the discrepancy between the variation of the physical properties of Ce1-xYbxCoIn5single crystals and thin films with Yb composition

“…The errors in such concentration measurements are about 5%. A similar approach was used to determine the Zn concentration in Zn doped LiNbO 3 [Bridges12]. The measured Ce concentrations are close to the nominal values, but the Yb concentrations are much lower than expected.…”

No difference in local structure about a Zn dopant for congruent and stoichiometricLiNbO3

“…In an earlier study 10 , we investigated the local structure in Zn doped congruent materials for a range of higher Zn concentrations using the EXAFS (extended x-ray absorption fine structure) technique, at both the Zn and Nb K edges. The environment about Zn was nearly identical for all Zn concentrations with a small increase in local disorder for the higher concentration samples.…”

EXAFS simulations in Zn-doped LiNbO3based on defect calculations

“…The final simulated EXAFS was taken to be the average of the four individual simulations. The Debye-Waller factor was set to 0.003Å -2 that is a typical value for low temperature measurements and is close to the experimental values fitted to the EXAFS data in refs [4] and [5]. Figure 1 shows the simulated Fourrier transform of the EXAFS oscillations (red curves) for the model where Zn substitutes for the Li site ( figure 1(a)) and substitutes at the Nb site ( figure 1(b)) but considering the perfect lattice site with no distortion.…”

“…The clusters, thus, already include the lattice distortion around the Zn ions due to the defect generated in the LiNbO3 lattice and since both the dopant and the charge compensating defects were included in the defect calculations, the distortion represents more accurately the system. The defect modelling calculations were done at 0K and this temperature was chosen due to the fact that the experimental data from refs [4] and [5] were measured at low temperature.…”

“…Recent EXAFS studies ( [4], [5]) suggest that Zn occupies the Li site, and the model was based on assuming as …”