Microstructure and defects probed by Raman spectroscopy in lithium niobate crystals and devices

Chapron

Journal of Applied Physics

et al. 2017

Self Cite

Raman measurements were investigated on Zr -doped lithium niobate LiNbO 3 crystals with different concentrations. Spectra were treated by fitting procedure and principal component analysis which both provide results consistent with each other. The concentration dependence of the frequency of the main low-frequency optical phonons gives an insight of site incorporation of Zr ions in the host lattice. The threshold concentration of about 2% is evidenced, confirming the interest of Zr doping as an alternative to Mg doping for the reduction of the optical damage in lithium niobate.

Section: Experimental Results and Analysismentioning

confidence: 99%

“…Among all Raman lines we paid attention to those which can be used as the discriminating markers of sites A or B [17]. Thus, The concentration of Zr samples in samples under study is small (below 2.5 %) i.e.…”

Section: Introductionmentioning

confidence: 99%

Zr doping on lithium niobate crystals: Raman spectroscopy and chemometrics

Chapron

Journal of Applied Physics

et al. 2017

Self Cite

“…At the same time, the octahedral coordination of cations by oxygen ions allows significant geometric distortions of octahedra LiO 6 , NbO 6 , MeO 6 , O 6 , ( is a vacant octahedron) without changing their symmetry. This fact, along with a large number of point defects in the cation sublattice, leads to structural and optical ununiformity of LN crystal and to formation of complex ionic complexes and microstructures (clusters) in the main (primary) crystal structure, i.e., to the formation of a widely developed secondary crystal structure [6,[10][11][12][13]. By primary (basic) crystal structure we mean a structure that can be experimentally determined by diffraction methods-neutron scattering and X-ray structural analysis.…”

mentioning

confidence: 99%

“…Once dopant concentration reaches threshold, the mechanism of doping cation incorporation to a structure changes and the properties of the crystal change too. This phenomenon attracts the close attention of researchers [3][4][5][6]10,11,[14][15][16][17]. The space group of the LN crystal does not change, even doped with high (above the threshold) concentrations of Mg 2+ and Zn 2+ , despite the significant change in the state of its defectiveness.…”

mentioning

confidence: 99%

“…The cluster structure has usually a lower symmetry than the structure of the main matrix [29][30][31]. The main (Li + and Nb 5+ ) and doping cations in the cluster are in low-energy positions, which leads to a distortion of oxygen octahedra and a change in spontaneous polarization [5,6,11,16]. Doping metals influence the secondary structure of LN crystals particularly strong near concentration thresholds when the mechanism of the doping cation incorporation into the lattice changes [5,6,[14][15][16].Modern technologies provide growth of optically perfect LiNbO 3 crystals with different Li/Nb ratios-nominally pure and doped with a wide range of metal elements.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Raman Scattering in Non-Stoichiometric Lithium Niobate Crystals with a Low Photorefractive Effect

2019

Raman spectra of lithium niobate single crystals strongly doped by zinc and magnesium, it has been established, contain low-intense bands with frequencies 209, 230, 298, 694, and 880 cm −1 . Ab ignition calculations fail to attribute these bands to fundamental vibrations of A 2 symmetry type unambiguously. Such vibrations are prohibited by the selection rules in the space group C 3V 6 (R3c).Ab initio calculations also proved that low-intense "extra" bands with frequencies 104 and 119 cm −1 definitely do not correspond to vibrations of A 2 symmetry type. We have paid special attention to these extra bands that appear in LiNbO 3 single crystals Raman spectra despite the fact that they are prohibited by the selection rules. In order to do so, we have studied a number of lithium niobate single crystals, both nominally pure and doped, by Raman spectroscopy. We have assumed that some "extra" bands correspond to two-particle states of acoustic phonons with a total wave vector equal to zero. We have also detected a Zn concentration area (0.05-0.94 mol.% ZnO in a crystal) where doped crystal structure is more ordered: The order of alternation of the main, doping cations, and vacancies along the polar axis is increased, and oxygen octahedra are less distorted.Crystals 2019, 9, 535 2 of 37 changes. Features of the LN crystal structure determine features of its vibrational spectrum and many other physical characteristics. LN single crystal is a material with a widely developed secondary structure. It is important to note that the fine features of its structure and, accordingly, the physical characteristics can be significantly changed by changing the composition (changing the Li/Nb ratio and doping), as well as by changing the structure and physicochemical properties of the melt [3][4][5][6]. Moreover, the oxygen-octahedral structure allows doping of the crystal with high (several wt.%) concentrations of metals, as well as double and triple doping with different elements with different charge states.When interpreting the experimental results, the crystal should be considered as a solid solution of Me:Nb:LiNbO 3 (Me is a doping metal). Many metals are capable of entering the octahedral voids of the structure; the solubility limits of the metals are rather large. The concentration of doping metals in the crystal LN structure can reach several wt. % and accordingly~9 mol.% [2][3][4][5][6]. At the same time, the octahedral coordination of cations by oxygen ions allows significant geometric distortions of octahedra LiO 6 , NbO 6 , MeO 6 , O 6 , ( is a vacant octahedron) without changing their symmetry. This fact, along with a large number of point defects in the cation sublattice, leads to structural and optical ununiformity of LN crystal and to formation of complex ionic complexes and microstructures (clusters) in the main (primary) crystal structure, i.e., to the formation of a widely developed secondary crystal structure [6,[10][11][12][13]. By primary (basic) crystal structure we mean a structure that can be experimentally de...

Synthesis, Characterization, and Second Harmonic Generation of Multiferroic Iron‐Doped Lithium Niobate Powders

García‐Rodríguez,

Sánchez‐Dena,

Velasco‐Cortez

et al. 2023

Adv Elect Materials

Random granular media can exhibit characteristics that are often related to ordered media. In the present work, this feature is observed in the polarized Second Harmonic Generation (SHG) response from reduced iron‐doped lithium niobate (LN:Fe) powders, which is an unexpected effect due to multiple scattering. In addition, the subsisting‐order properties of the powders can be further controlled by magnetic induction to tailor the SHG response. The samples are characterized by X‐ray Diffraction (XRD), X‐ray Photoelectron Spectroscopy (XPS), and confocal Raman Spectroscopy. The SHG response in the absence and presence of an external static magnetic field is then studied as the fundamental beam focus is translated from air into the powder. The SHG intensity polarization state is studied as a function of the linear polarization of the fundamental beam at the focus depth position, where the maximum SHG recorded intensity is observed. These results demonstrate that the SHG response of LN:Fe powders can be modified by post‐thermal treatment in a reducing atmosphere for photonic applications.