Investigations on Crystalline Perfection, Raman Spectra and Optical Characteristics of Transition Metal (Ru) Co-Doped Mg:LiNbO3 Single Crystals

Congruent lithium niobate single crystals with a Ru:Mg co-dopant have been successfully grown using the Czochralski technique from the melt containing 0.02 mol % Ru with Mg of two varied concentrations (4.0 and 6.0 mol %). The effects of Ru and Mg co-doping on the crystalline quality were determined by high-resolution X-ray diffractometry, which confirmed that the crystalline quality is good and that the dopants are statistically distributed in the crystal. The Raman scattering analysis shows no change in the lattice vibration except a slight change in the peak width and intensity due to more asymmetry in the molecular charge, which leads to enhancement of the polarizability. The optical transmission spectra indicate that both the crystals have high optical transparency in the visible region, with a shift of the absorption edge toward shorter wavelengths, as compared to un-doped LN. The weak absorption band observed below 400 nm is attributed to Ru ions. The influence of co-doping in the electronic band gap energies is calculated by the Tauc relation. The refractive index is measured by using a prism coupler at two wavelengths (532 and 1064 nm). The calculated absorption coefficients and direct and indirect band gap energies for both the samples are found to be nearly the same within experimental error. A decrease in the birefringence is observed for the Ru:Mg(6 mol %) doped sample. The observed slight reduction in refractive indices with Ru:Mg co-doping is consistent with a rise in band gap energy, which is related to the change in absorption edge to the lower wavelength. The second harmonic generation (SHG) efficiency is measured by the Kurtz and Perry powder method, and a decrease in SHG efficiency for Ru:Mg(6 mol %) is observed.

Investigation of the Defect Structure of Congruent and Fe-Doped LiNbO₃ Powders Synthesized by the Combustion Method

Fe-doped LiNbO₃ synthesized by the combustion method to seek new multiferroic materials exhibits room-temperature ferromagnetism, as reported in our previous work. In this work, the defect structure of congruent and Fe-doped LiNbO₃ (0.57–3.3 mol %) powders was investigated in detail by several methods. The molar ratio of [Li]/([Li]+[Nb]) was determined by the Curie temperature (T_c) via DSC. Two peaks of T_c were observed due to phase splitting, and the phase at lower T_c disappears as the Fe doping concentration increases. The coexistence of two different oxidation states of Fe ions in LiNbO₃ was probed by XPS and UV-Vis spectroscopy. The Raman spectra exhibit displacements along the c axis of Li and Nb ions, and a deformation of the NbO₆ framework owing to Fe doping. Several doping models were applied in the Rietveld refinement of powder X-ray diffraction collected by synchrotron radiation. The fitting by the Nb vacancy model leads to an improbably distorted structure of congruent LiNbO₃. In Fe-doped LiNbO₃, we conjecture that Li and Nb vacancies coexist in the lattice structure; Fe⁺²/Fe⁺³ ions are substituted for Li ions at the regular Li site and may push the anti-site Nb_Li ion back to the regular Nb site.

An in-depth study into the growth aspects and characteristic properties of ethyl 4-amino benzoate: a potential candidate for electro-optical applications

We present the bulk growth and characterization of an EPAB crystal using a single zone transparent resistive furnace.

Crystallographic, optical and dielectric properties of gel grown praseodymium malonate single crystals

Single crystals of praseodymium malonate hexahydrate are grown by gel encapsulation technique.

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

Mg-doped congruent lithium niobate single crystals were grown by the Czochralski technique. High-quality single crystals were grown using a novel seeding technique in a resistive heating furnace. Analysis of crystalline perfection carried out by a multi-crystal X-ray diffractometer revealed that the grown crystals do not contain any structural grain boundaries but do contain point defects. The transmission characteristics showed an enhancement of band gap with an increase in Mg concentration. Conoscopy patterns revealed that the grown crystals are homogeneous and the incorporation of Mg into the lattice does not affect the optical sign (negative uniaxial) of the crystal. The refractive index measurements carried out using a prism coupler showed an increase in the optical birefringence (Δn), while the refractive index was found to decrease with the increase in doping concentration. Further, thermal conductivity was found to decrease with Mg incorporation in the lattice owing to phonon scattering from the Mg ions and, as a consequence, at high concentrations (>4 mol%) crack formation occurred. However, optimization of growth conditions reveals that a slower pulling rate leads to crack-free lithium niobate crystals even at 6 mol% Mg doping.

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

Zr–Fe-doped congruent lithium niobate single crystals were grown by the Czochralski technique. The crystal structure and lattice parameter of the grown crystals were assessed by powder X-ray diffraction and the strain developed as a result of doping has been calculated (−1.19 × 10−3) by using the Williamson–Hall relation. The incorporated dopant concentration along with the dopant distribution in the specimen crystal was estimated by X-ray florescence spectrometry. A multi-crystal X-ray diffraction analysis was carried out to identify the crystalline perfection of the sample and revealed that the investigated crystal does not contain any structural grain boundaries but does contain point defects and micrometre size mosaic blocks. Birefringence measurements were carried out using a prism coupler spectrometer and found that the optical birefringence is 0.0822 for 532 nm and 0.705 for 1064 nm. A thermal conductivity (κ) study reveals that the doped sample has a lower κ value than the undoped equivalent.

Growth, crystalline perfection and characterization of hexaaquanickel(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate crystals

Pale-green single crystals of hexaaquanickel(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate K(2)[Ni(H(2)O)(6)] (C(8)H(5)O(4))(4)·4H(2)O (PNHP), of dimension ~33 mm × 18 mm × 4 mm have been grown by slow evaporation solution growth technique (SEST) and modified Sankaranarayanan-Ramasamy (SR) method. The powder XRD profiles and FT-IR are used for identifying the material. The lattice parameters of the as-grown crystals obtained by single crystal X-ray diffraction analysis confirm the formulae. Lower optical cut-off at ~300 nm and optical transparency in the visible region were observed. The structural perfection of the grown crystal has been analyzed for SEST and SR method grown crystals by high-resolution X-ray diffraction (HRXRD) rocking curves (DC). The DCs of both the specimens are asymmetric with respect to Bragg position and more of scattered intensity in the negative direction is indicative of predominantly vacancy defects. Interestingly, SR method grown crystal has a better crystalline perfection than the conventionally grown crystal. The dielectric, thermal and mechanical behaviors of the specimen were also studied.

The effect of Cr3+doping on the crystalline perfection and optical properties of zinc tris(thiourea)sulfate, a nonlinear optical material

A study of the effect of Cr3+doping in zinc tris(thiourea)sulfate (ZTS, a well known nonlinear optical material) single crystals on crystalline perfection and optical properties was carried out. Pure and chromium-doped (1 and 2 mol%) ZTS single crystals were grown by the slow evaporation solution technique. The actual concentration of chromium incorporated into the crystal lattice was found to be different, as evaluated by flame atomic absorption spectroscopy. High-resolution X-ray diffraction (HRXRD) analysis revealed that chromium doping led to the creation of vacancies in the grown single crystals. The photoluminescence emission spectra of pure and doped crystals supported the HRXRD findings. The optical band gap of the single crystals increased as a result of the Cr3+doping, but their transparency in the visible region decreased. The doped crystals exhibited higher linear refractive indices than the pure crystals. The optical dielectric constant (∊), the extinction coefficient (k), the average single-oscillator energy for electronic transitions (Eo) and the oscillator strength (Ed) were evaluated for ZTS single crystals and significant changes were observed in these parameters due to the Cr3+doping.