Defect structure of highly Zn-doped LiNbO3 single crystal revealed by extended x-ray absorption spectra

Abstract

To determine the defect structure of ZnO-doped LiNbO3 single crystals with high doping concentrations, we obtain the measurements using the extended x-ray absorption fine structure (EXAFS) at room temperature. It indicates Zn atom is directly substituted on the Li site of the LiNbO3 crystal after Zn doping. EXAFS simulation by way of analyzing the scattering amplitudes also shows that the Zn atom does not substitute the Nb site at highly Zn-doped LiNbO3. Finally, we confirm that VNb5−, a strong charged vacancy, should be considered as an important factors in influencing the physical properties of LiNbO3 beyond 7.5mol% Zn-doped doping concentration.

EXAFS evidence for a primary ZnLidopant in LiNbO3

“…The fits are not sensitive to small amounts of Zn but are inconsistent with more than one Zn neighbor; thus all our data are inconsistent with a significant clustering of Zn that is needed for some defects such as five Zn Li surrounding a Nb vacancy. 23 The detailed analysis also shows that the three nearest O neighbors to Zn (first peak) are slightly pulled inward by 0.05Å while the nearest Nb metal atoms are pushed away by 0.07Å; further O and Nb shells have a similar but smaller displacement. Calculations for Zn on a Li site plus a Li vacancy show similar behavior.…”

“…There have been many efforts-both theoretical [5][6][7][8][9][10][11][12][13][14] and experimental 3,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] -to investigate intrinsic and extrinsic defects. For undoped, congruent LNO each antisite Nb 6 Adding divalent and/or trivalent metal dopants produces extrinsic defects that modify important optical properties and also change the lattice constants, 17,30 particularly near and above the so-called threshold concentration of ∼7 mol %.…”

“…Room-temperature (RT) measurements for very dilute (<1 mol %) Ti +4 and Ni +2 suggest substitution mainly at the Li site 15 while similar RT measurements on Hf-and Hf/Mg-doped samples indicate that 1 mol % Hf substitutes at the Li when no Mg is present but at large Mg dopings (6 mol % Mg) the Hf substitutes on Nb sites. 16 One Zn EXAFS (extended x-ray absorption fine structure) experiment 23 did show Zn K-edge data at room temperature that indicated little change in the EXAFS with increasing Zn composition; they reported substitution on the Li site but no analysis was given. Instead they focused more on the Nb K-edge EXAFS data, and proposed a Nb vacancy model with five Zn Li surrounding the vacancy (5Zn…”

Effect of Mg doping on the growth aspects, crystalline perfection, and optical and thermal properties of congruent LiNbO3single crystals

“…However, when it is doped with dopants like Mg to mask its defects, specifically an Li vacancy (with a view to improving its efficiency), the system can respond in a different manner, leading to changes in the point defect distribution, the formation of dislocations and finally the appearance of structural boundaries (Bhagavannarayana, Ananthamurthy et al, 2005). These defects sometimes mask or cause a partial/complete deterioration in some of the anisotropic physical properties of single crystals and reduce the efficiency of devices made out of these crystals (Tsai et al, 2008;Bhagavannarayana et al, 2006). Therefore, to realize the full efficiency of the devices, the crystal must be free from such structural defects and hence its crystalline perfection should be assessed before its active usage, particularly when it is doped.…”

Structural, optical and thermal properties of Zr–Fe co-doped congruent LiNbO3single crystals

“…However, the addi-tional dopants normally induce high geometric strains in the lattice, and while the crystal tries to relax, the dynamics of point defects result in the agglomeration of point defects, formation of dislocations and finally the formation of structural boundaries (Bhagavannarayana et al, 2005). These defects mask or partially/completely degrade some of the anisotropic physical properties of single crystals and reduce the efficiency of the devices made out of these crystals (Xu et al, 2009;Tsai et al, 2008;Bhagavannarayana et al, 2006). In this article, we report the effect of Zr-Fe doping on the strain generated in a cLN crystal using powder and high-resolution X-ray diffraction.…”