EXAFS evidence for a primary Zn Li dopant in LiNbO 3

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 (7-11mol%) 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 4; 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 3.7. 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. Show more