Structural defects in congruent and near-stoichiometric LiNbO₃

Abstract

A comparative study of LiNbO3 single crystals with congruent and near-stoichiometric compositions was performed using hyperfine interactions and ion beam techniques. Our data show that the structure of congruent LiNb03 cannot be completely dcscribed by the models which assume only vacancies and Nb antisites. Additional disorder has to be considered both at the Li and Nb sites. The additional defects are cation stacking inversions, in which the cation sequence coincides locally with the one of ilmenite-like LiNb03. We suggest that these stacking inversions are associated with the Nb antisites necessary for charge compensation in Li-deficient material.

Unveiling the Defect Structure of Lithium Niobate with Nuclear Methods

“…A comparison was also made with PAC. Figure 10 shows PAC spectra obtained with the 111 In probe in the same near-stoichiometric crystal grown with 4.6 wt % K 2 O after implantation and annealing [63], compared with a spectrum previously obtained in a congruent crystal [53]. It is clear that the spectrum with the highest attenuation is the one obtained in the congruent crystal.…”

Lattice location of Hf and its interaction with other impurities in LiNbO3: a review

“…17 Minzioni et al have suggested that the threshold is connected with the occupation of Nb sites by Hf. 17 However, our data have shown that Hf starts occupying Nb sites well below 2 mol% doping, 78 suggesting that the threshold at 3 to 4 mol% is rather linked to the dissolution of the intrinsic stacking inversions, 39 which must happen subsequently to the dissolution of the Nb antisites.…”

“…57 It was proposed that the intrinsic defects associated with Li II sites were short stacking inversions that match the cation sequence of ilmenite around the Nb antisites. 39 Figure 7 shows the stacking sequences along the c-axis for (a) perfect LN, (b) ilmenite-like LN, (c) LN with an antisite Nb, creating a sequence of three consecutive Nb atoms, and (d) a stacking inversion next to the Nb antisite.…”

“…7) after implantation with 111 In and annealing at 800°C. 39 The crystals were oriented with the c-axis perpendicular to the plane of the detectors. The corresponding spectrum obtained in a congruent LN crystal is also shown for comparison.…”

The 181Hf/181Ta Probe in the Li and Nb Sites of Congruent Linbo3 Co-doped with Mg and Cr Ions Studied by γ–γ PAC

“…Two QIF, n Q1 = 191(2) MHz and n Q2 = 205(2) MHz, with non-zero h were previously found in pure congruent crystals implanted with 111 In [4], while for near-stoichiometric crystals only one QIF, n Q1 = 191(2) MHz with h = 0 was observed [7]. Thus, both the existence of n Q2 and the nonzero h values were attributed to a stoichiometry-related defect.…”