Papers by Keyword: Lithium Niobate

Abstract: It was shown that laser conoscopy can visually detect even slight changes in the optical characteristics of a crystal when it is doped. It has been found that the defective structure of LiNbO₃:Zn (4.5 mol. %), LiNbO₃:Mg (3.0–5.5 mol.%) crystals associated with an uneven entry of an impurity leads to a local change in the elastic characteristics of the crystal and the appearance of mechanical stresses that distort the conoscopic patterns. This can be an abnormal optical biaxiality, which manifests itself in the form of a rupture and enlightenment of the "Maltese cross" in the center of the conoscopic crystal pattern, or local birefringent inclusions that are recorded as additional interference patterns against the background of the main conoscopic pattern, both in the center of the field of view and in its peripheral area.

Abstract: The features of the structure of single crystals LiNbO₃:B³⁺ (0.12 and 0.18 wt %) grown by the Czochralski method from the mixture of different genesis were studied. It was found that boron is able to incorporate into the crystal structure of lithium niobate in a trace amounts (~ 10^–4–10^–5 wt %), decreasing the concentration of structural defects Nb_Li. Thus, ordering of structural units of the cation sublattice of lithium niobate crystals grown from a congruent composition melt approach in that of stoichiometric crystals.

Abstract: A successful growth of the titanium-doped lithium niobate (Ti: LiNbO₃) single crystal by Czochralski method is reported. By preserving an effective control of growth parameters such as maintaining accurate temperature gradient by controlling its output power and growth rate as well as wisely choosing the right pulling rate and speed rotation, the Ti:LiNbO₃ single crystal successfully produced using Automatic Diameter Control-Crystal Growth System (ADC-CGS). The structural and optical analyses have been done by using X-ray Diffractometer (XRD), Differential Thermal Analyzer (DTA) and Ultraviolet-Visible (UV-Vis) spectroscopy. The crystallinity of the sample has been confirmed using XRD and DTA has been used to determine the crystal nature of the sample. The position of fundamental absorption edge was recorded via transmission spectra in UV and visible region.

Abstract: High temperature piezoelectric materials have numerous potential applications, including high temperature ultrasound NDT, MEMS, sensors, or actuators. However, conventional piezoelectric materials are unsuitable for operation above 400°C. Lithium niobate (LiNbO₃) is a promising candidate because of its very high Curie temperature (approximately 1210°C) and reasonable piezoelectric coefficients. However, the piezoelectric properties are not sufficiently understood, partly due to the difficulties in characterizing this behavior at high temperature. Degradation mechanisms well below the Curie temperature, suspected to include phase transformations, oxygen loss, and excessive ionic conductivity, further deteriorate this property. In order to better understand these physical mechanisms, electrochemical impedance spectroscopy (EIS) is used to characterize monocrystalline LiNbO₃ from room temperature to 500°C, with excitations from 20 Hz to 20 MHz. An equivalent circuit model analysis, including resonant frequencies, is developed to investigate the temperature dependence of the piezoelectric behavior, as well as the mechanical elasticity and damping. Numerical values extracted from this analysis allows for numerical simulations to model device behavior.

Abstract: Lithium niobate nanostructured thin films were deposited on (100) N-type Si substrates. Spin coating technique was used employed the polymeric precursor method (Pechini process) . The prepared films were Annealing in static air and oxygen atmosphere was performed at 500 _C for 2 h. X-ray diffraction analysis and SEM properties was carried out for films prepared at different mol concentration (0.25,0.50,0.75,1.00) Mol%. The results show a good enhancement in both structural and surface morphology of the films with increasing the concentration

Abstract: Lithium transport through ultrathin silicon layers can be measured non-destructively by neutron reflectometry (NR) using a multilayer composed of silicon layers embedded between solid state Li reservoirs. An established model system is a multilayer with a repetition of five [Si / ^natLiNbO₃ / Si / ⁶LiNbO₃] units. Two types of Bragg peaks are detectable in reflectivity patterns. These Bragg peaks result from the interference of neutrons reflected at periodic interfaces. One type of Bragg peak originates from the periodicity of the LiNbO₃/Si chemical contrast (first order peak), while the other Bragg peak results from a superstructure with double periodicity. This superstructure may arise from ⁶Li/⁷Li isotope contrast or alternatively from periodic thickness variations, as shown by simulations based on the Parratt algorithm. The intention of the present paper was to elucidate the origin of the second Bragg peak. Experiments done by Secondary Ion Mass Spectrometry (SIMS) isotope sensitive depth profiling showed in a direct way that annealing at 360 °C destroys indeed the ⁶Li/⁷Li contrast, whereas the LiNbO₃/Si chemical contrast remains unchanged. This evidences that the experimentally observed decrease of the second Bragg peak in the reflectivity pattern during annealing is a measure for Li transport through the Si layer.

Abstract: A Lithium niobate (LiNbO₃) based integrated optical E-field sensor with an optical waveguide Mach-Zehnder interferometer (MZI) and a tapered antenna has been designed and fabricated for measurement of pulsed E-field. Experimental results demonstrate that the minimum detectable E-field of the sensor is 10 kV/m. The linear relationship between the sensor input and output is better while the input E-fields varied from 10 kV/m to 370 kV/m. Besides, from the fitting curve it can be calculated that the maximum detectable E-field of the sensor is approximately equal to 1000 kV/m.

Abstract: Channel waveguide formed by multi-energy O²⁺ ion implantation with different doses is analyzed at both 633 and 1539 nm. It has been demonstrated that the transverse mode number of waveguide is governed by the practical width of the channel waveguide, which depends on not only the channel width from pattern mask, but the lateral straggling of implanted ions. Beam propagation method (BPM) is employed to simulate the possible propagation transverse mode in the waveguides with different widths. The results at 1539 nm show that the waveguide keeps being a single mode waveguide until the width of channel is greater than 15 μm. At 633 nm, TE₂₀ mode can be obtained even the width of channel is very small, and the TE₃₀ mode begins to appear when the width is greater than 9 μm. These simulation results are in good agreement with the experimental results and the calculated results from Marcatilis method.

Abstract: Ce:Mn:LiNbO₃ single crystals with different [L/[N were used for the measurement of Raman spectrum. Each peak appeared in the Raman spectrum was ascribed to the basic vibration modes of the LiNbO₃ crystal according to the basic analysis and the achievements obtained by the earlier researches. The results showed that the peak width at half height (FWHM) of the A₁(TO₁) vibration mode become wide gradually with the increase of the [L/[N. However, the FWHM of A₁(TO₂) and A₁(TO₄) vibration mode decrease with the increase of the [L/[N in the crystal. The FWHM of the E(TO₁) vibration mode was decrease with the increase of [L/[N in the crystal, and also the linear relationship between the FWHM of the E(TO₁) vibration mode and the [L/[N in the crystal. According to the relationship between the [L/[N in the crystal and the FWHM of the E(TO₁) vibration mode for the pure LiNbO₃ crystal, the quantitative relation for the Ce/Mn co-doped LiNbO₃ crystal was revealed by amending the empirical formula for pure LiNbO₃ crystal on the basis of the results measured by ICP-AES. The quantitative relation of the FWHM of the E(TO₁) vibration mode and the [L/[N was given by the Polynomial Fit of the experimental data.

Abstract: This paper reports on the luminescent properties of the congruent as-grown and vacuum annealed LiNbO₃ single crystals at the UV and X-ray excitations. The shape of excitation spectra is similar for all emission bands in as-grown sample as well as in vacuum annealed sample. The emission spectra (exc=235 nm) observed in the spectral region 250…800 nm at room temperature consist of five elementary bands. Correlation of the relative intensities bands in luminescence spectra under different types of excitation and their temperature dependencies were determined. The most intensitive maxima in as-grown sample are observed at 295 and 691 nm. The main maximum after vacuum annealing is peaked around 295 nm.