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

2021

Crystals

X-ray and neutron diffraction studies succeeded in the 1960s to determine the principal structural properties of congruent lithium niobate. However, the nature of the intrinsic defects related to the non-stoichiometry of this material remained an object of controversial discussion. In addition, the incorporation mechanism for dopants in the crystal lattice, showing a solubility range from about 0.1 mol% for rare earths to 9 mol% for some elements (e.g., Ti and Mg), stayed unresolved. Various different models for the formation of these defect structures were developed and required experimental verification. In this paper, we review the outstanding role of nuclear physics based methods in the process of unveiling the kind of intrinsic defects formed in congruent lithium niobate and the rules governing the incorporation of dopants. Complementary results in the isostructural compound lithium tantalate are reviewed for the case of the ferroelectric-paraelectric phase transition. We focus especially on the use of ion beam analysis under channeling conditions for the direct determination of dopant lattice sites and intrinsic defects and on Perturbed Angular Correlation measurements probing the local environment of dopants in the host lattice yielding independent and complementary information.

Section: Congruent Versus Stoichiometric Lithium Niobatementioning

confidence: 90%

Unveiling the Defect Structure of Lithium Niobate with Nuclear Methods

Kling

2021

Crystals

“…77 Codoping with K 2 O yields near-stoichiometric or stoichiometric crystals 7 although no K was found in the crystals by PIXE down to the detection limit of 100 ppm. 58 In all cases, Hf was found occupying Li and Nb sites. Figure 11 shows the PAC spectra and the respective Fourier analyses obtained with the near-stoichiometric crystal doped with 1 mol% HfO 2 and the congruent crystal doped with 6 mol% HfO 2 , with the c-axis of the LN crystals perpendicular to the plane of the PAC detectors.…”

Section: Factors Affecting the Lattice Location Of Hfmentioning

confidence: 99%

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

Lorenz

2014

Opt. Eng

Abstract. Lithium niobate, LiNbO3, exists in a wide range of compositions, from congruent to stoichiometric. Undoped congruent LiNbO3 suffers from a relatively low optical damage threshold that constitutes its major disadvantage for optoelectronic devices. The optical damage threshold is dependent on the amount of intrinsic defects and is considerably increased in stoichiometric material and in congruent material doped with specific impurities, such as Mg, In, Sc, and Zn. It has been recently shown that the doping with Hf leads to a significant increase of the photorefractive resistance at a threshold concentration of about 3 mol%. The study of the lattice location of Hf in LiNbO3 and its interaction with other impurities and intrinsic defects started more than a decade before the discovery of the role of this impurity, as Hf was a convenient probe for combined studies using the nuclear techniques perturbed angular correlations and Rutherford backscattering spectrometry/channeling. An integrated review of the main results obtained with these techniques is presented. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.OE.53.6.060901

“…The are fitted by E-" functions with IC = 0.69-0.78 for K5 and IC = 0.91-1 .OO for K12, indicating the existence of point-like defects. In a previous work we have shown that, in addition to the Li vacancy model, it was necessary to consider 2.5(5)% ilmenite stacking inversions to account for the disorder seen in congruent crystals [5]. However, it was not possible to decide if the inversions were diluted in the crystal or formed intergrowths as suggested in Ref.…”

Section: Discussionmentioning

confidence: 95%

“…The PAC data taken in the K5 and K12 crystals are in contrast with the data in congruent crystals, where two close frequencies, The two frequencies were attributed to the existence of two distinct Li sites in congruent crystals, while only one exists in near-stoichiometric crystals [5]. The observcd difference between K5 and K12 is accounted for by a time-dependent attenuation term, defined by the density of Fig.…”

Section: Discussionmentioning

confidence: 99%

Structural defects in congruent and near-stoichiometric LiNbO₃

Radiation Effects and Defects in Solids

Kling

Silva

et al. 1999

Self Cite

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.