Synthesis of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>〈B〉 solid precursors and LiNbO<Subscript>3</Subscript>〈B〉 batches and their phase compositions

A process has been developed for preparing boron-doped niobium pentoxides Nb₂O₅〈B〉 to be used as precursors in the sysnthesis of nithium biobate batches LiNbO₃〈B〉 having tailored dopant concentrations. Solutions of various origins were used to isolate Nb₂O₅〈B〉. A method has been advanced to account for boron loss as volatile compounds upon the heat treatment of niobium hydroxide in order to determine the boron amount to be added to niobium hydroxide in the form of H₃BO₃. The boron concentration in LiNbO₃〈B〉 during lithium niobate synthesis is shown to be independent of the origin of the Nb₂O₅〈B〉 precursor with the same as-batch boron concentration. The phase compositions of Nb₂O₅〈B〉 and LiNbO₃〈B〉 have been characterized by X-ray powder diffraction and IR spectroscopy and boron concentrations have been determined for the synthesis of single-phase lithium niobate batches for use in the production of optically uniform single crystals and pore-free piezoelectric ceramics.     

Composition and Homogeneity of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>〈В〉 Solid Precursors and LiNbO<Subscript>3</Subscript>〈В〉 Batches

Nb₂O₅〈В〉 solid precursors and LiNbO₃〈В〉 batches prepared on their basis, which can be used for preparing optical-quality lithium niobate single crystals and pore-free piezoelectric ceramics, have been studied by laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The compositions of powdery samples pelletized without binder have been determined. The calculated mean-square deviations Sr of laser ablation ICP-MS have been used to show a homogeneous distribution of the boron dopant over Nb₂O₅〈В〉 precursors and LiNbO₃〈В〉 batches.     

Synthesis of homogeneously mg-doped lithium niobate batch and study of the effect of non-metal impurities on the properties of LiNbO<Subscript>3</Subscript>:Mg crystals

The preparation conditions for the homogeneously doped precursor Nb₂O₅:Mg for the synthesis of granulated lithium niobate batch was studied. The effect of non-metallic impurities in the Nb₂O₅:Mg precursors and the lithium niobate batch on the characteristics of the melt–crystal system and the physicochemical and optical characteristics of the LiNbO₃:Mg crystals was established.     

Composition investigation of lithium niobate crystals and its influence on the optical damage resistance

Optical methods of investigation of the defect structures and the composition of lithium niobate (LiNbO₃) single crystalsis discussed. The intrinsic defects concentrations in lithium niobate crystals (lithium vacancies (V_Li)⁻ and (Nb_Li)⁴⁺ defects, Nb on Li site in the valence state 4+), as a function of the Li/Nb ratio, are also reported. The optical damage resistance of various lithium niobate samples was investigated as a function of the composition. A remarkable increase in the optical damage resistance was found in MgO-doped almost stoichiometric lithium niobate crystals.     

Tetrahydrofuran Activation Assisted Synthesis of Nanosized Lithium Niobate and Lithium Tantalate

Black solid precursors obtained from reactions between MCl₅ (M = Nb, Ta) and alkyllithiums, n‐butyllithium (ⁿBuLi) and ethyllithium (EtLi), in tetrahydrofuran (THF) were heat treated under vacuum at 673–973 K to form nano‐sized particles (20–100 nm in diameter) of lithium niobate (LiNbO₃) and lithium tantalate (LiTaO₃). Stoichiometry of the reactants is critical and affects the phases of the products. Based on the volatile byproducts detected, a reaction pathway involving the activation of THF by alkyllithiums is proposed to be important for the formation of LiNbO₃ and LiTaO₃ precursors.     

State of the Art in Crystallization of LiNbO3 and Their Applications

Lithium niobate (LiNbO₃) crystals are important dielectric and ferroelectric materials, which are widely used in acoustics, optic, and optoelectrical devices. The physical and chemical properties of LiNbO₃ are dependent on microstructures, defects, compositions, and dimensions. In this review, we first discussed the crystal and defect structures of LiNbO₃, then the crystallization of LiNbO₃ single crystal, and the measuring methods of Li content were introduced to reveal reason of growing congruent LiNbO₃ and variable Li/Nb ratios. Afterwards, this review provides a summary about traditional and non-traditional applications of LiNbO₃ crystals. The development of rare earth doped LiNbO₃ used in illumination, and fluorescence temperature sensing was reviewed. In addition to radio-frequency applications, surface acoustic wave devices applied in high temperature sensor and solid-state physics were discussed. Thanks to its properties of spontaneous ferroelectric polarization, and high chemical stability, LiNbO₃ crystals showed enhanced performances in photoelectric detection, electrocatalysis, and battery. Furthermore, domain engineering, memristors, sensors, and harvesters with the use of LiNbO₃ crystals were formulated. The review is concluded with an outlook of challenges and potential payoff for finding novel LiNbO₃ applications.     

Chemical effects on ArF excimer laser irradiated surfaces of single crystalline lithium niobate

Single crystalline lithium niobate was irradiated by ArF excimer laser and the surface morphological changes were observed. It was found that various deffects occured in dependence on the laser beam energy density and the number of pulses. Delayed formation of microcracks was observed, which can be explained by the chemical reaction of LiNbO₃ with atmospheric water.     

Niobium(V) oxide doped with Mg<Superscript>2+</Superscript> and Gd<Superscript>3+</Superscript> cations: Synthesis and structural studies

Methods for direct doping of niobium pentoxide with photovoltaically inactive Mg²⁺ and Gd³⁺ cations were developed for subsequent use in the synthesis of a stock for growing single crystals of lithium niobate with improved optical characteristics. The Raman spectra of doped pentoxides Nb₂O₅: Mg and Nb₂O₅: Gd revealed their island structures.     

Comparative investigation of LiNbO3 crystals Raman spectra in the temperature range 100–400 K

We have investigated Raman spectra of congruent and stoichiometric LiNbO₃ crystals in the temperature range 100–450 K. Slope gradient is greater for the temperature dependence of band width associated with Nb⁵⁺ ions vibrations than that associated with Li⁺ ions vibrations in a lithium niobate crystal structure. This fact indicates that the anharmonicity of Nb⁵⁺ ions vibrations along the polar axis is greater compared to Li⁺ ions vibrations. It is likely that O^2– ions contribute to this anharmonicity. The O^2– ions vibrations are characterized by an anharmonic potential in the LiNbO₃ crystal structure. The O^2– ions vibrations according to ab initio calculations strongly interact with vibrations of Nb⁵⁺ ions. We have found that the temperature dependence of the fundamental bands intensity is nonmonotonic and the “extra bands” intensity is strictly linear.     

Investigation of lithium niobate composition by optical spectroscopy methods

Indirect methods of investigation of composition and defect structures of lithium niobate (LiNbO₃) single crystals with different compositions are discussed. The analysis of two methods for the determination of the Li/Nb ratio in the samples is carried out, viz., the fundamental UV absorption edge and IR vibrational spectra of the OH⁻ group defects. Intrinsic defect concentrations in lithium niobate crystals (lithium vacancies, $ V_{Li^ - } $ V_{Li^ - } and defects, $ Nb_{Li^{4 + } } $ Nb_{Li^{4 + } } ) as a function of the Li/Nb ratio in the samples are given. The results obtained can serve as an effective way of express non-destructive composition analysis in a mass production of parallel-plane plates.     

Proton-exchanged waveguiding layers in Y-cut lithium niobate: Analysis of the phase composition by spectroscopic methods

A combination of methods was used for analysis of the phase composition of proton-exchanged layers in Y-cut lithium niobate. Mode spectra were used for the determination of phases. Vibration spectra allow some comparative and semi-quantitative estimations of the thickness of phase sub-layers to be made. The demonstrated method can contribute to adjustment of fabrication conditions for obtaining of defined phase compositions needed for waveguide devices with improved stability and characteristics.It was shown that deep and strongly protonated waveguides in Y-cut LiNbO₃ could be obtained at specific technological regimes.     

Investigation of new fluxes for the single-crystal growth of stoichiometric lithium niobate

Thermoanalytical and crystal growth investigations of the ternary system Cs₂O-Li₂O-Nb₂O₅ are presented in order to grow stoichiometric LiNbO₃ (LN) crystals. Part of the phase diagram is determined and subsolidus phases are identified at room temperature by X-ray powder diffraction. Among the constituent phases, a new tetragonal cesium lithium niobate phase is assessed. From the Cs₂O-Li₂O-Nb₂O₅ system, good quality quasi-stoichiometric LN crystals can be grown.     

A one-step solvothermal route for the synthesis of nanocrystalline anatase TiO2 doped with lanthanide ions

A one-step solvothermal synthesis is proposed for the preparation of nanocrystalline single-phase TiO₂ in the anatase form doped with lanthanide ions Eu³⁺, Er³⁺ and Sm³⁺. The structural properties of these products have been investigated by using X-ray powder diffraction, electron microscopy and Raman spectroscopy. Furthermore, the laser-excited luminescence spectra of the samples have been measured and analyzed. Following this route, the doping process turns out to be highly favorite and the resulting materials show an efficient luminescence in the visible region.     

Trace characterisation of lithium niobate by neutron activation analysis

Summary Coprecipitation behaviour of As, Au, Co, Cr, Cu, Eu, Fe, Ir, La, Lu, Mn, Mo, Nb, Ni, Pd, Pt, Sb, Sc, Ta, W, Zn and Zr during precipitation of hydrous oxide of niobium from lithium niobate was investigated. The matrix was dissolved in HF-HNO₃, evaporated to dryness and niobium was precipitated from HNO₃-H₂O₂ medium. The recovery studies were made using radiotracers. A radiochemical separation scheme based on group precipitation has been developed for the determination of Au, Co, Cr, Cu, Fe, Mn, Ni, Pd, Pt, Zn, Zr and rare earth elements. The method was applied to the analysis of lithium niobate. This analysis has provided fruitful information for improving the quality of the crystal.     

Sol-gel synthesis of nanocomposite materials based on lithium niobate nanocrystals dispersed in a silica glass matrix

With the final goal to obtain thin films containing stoichiometric lithium niobate nanocrystals embedded in an amorphous silica matrix, the synthesis strategy used to set a new inexpensive sol-gel route to prepare nanocomposite materials in the Li₂O-Nb₂O₅-SiO₂ system is reported. In this route, LiNO₃, NbCl₅ and Si(OC₂H₅)₄ were used as starting materials. The gels were annealed at different temperatures and nanocrystals of several phases were formed. Futhermore, by controlling the gel compositions and the synthesis parameters, it was possible to obtain LiNbO₃ as only crystallizing phase. LiNbO₃-SiO₂ nanocomposite thin films on Si-SiO₂ and Al₂O₃ substrates were grown. The LiNbO₃ average size, increasing with the annealing temperature, was 27 nm for a film of composition 10Li₂O-10Nb₂O₅-80SiO₂ heated 2 h at 800 °C. Electrical investigation revealed that the nanocrystals size strongly affects the film conductivity and the occurrence of hysteretic current-voltage curves.     

Lithium-Ion conducting oxides: Synthesis,structure, and electroconducting properties

The properties of perovskite type ABO₃ lithium-ion conducting oxides based on lanthanum lithium titanate (La,Li)TiO₃, lanthanum lithium niobate and tantalate, and Li₅La₃M₂O₁₂ (M = Nb, Ta) garnets were considered. Approaches to modification of the properties of these oxides, as well as the charge-compensation mechanisms associated with nonisovalent doping were discussed. Special consideration was given to phase formation and crystal structure in relation to the composition and preparation conditions of the oxides.     

LiNbO3 and LiTaO3 thin films deposited by chemical and/or physical processes

Lithium niobate LiNbO₃ thin films were deposited onto silicon (111) Si and sapphire (001) AI₂O₃ single crystal substrates by the pyrosol and/or r.f. sputtering processes. A matrix of experiments was designed to determine the effects of several experimental parameters on the resulting film quality (stoichiometry, crystallization state) and properties. Under optimized conditions, requiring the combination of the two above-mentioned deposition techniques, <001 > oriented polycrystalline LiNbO₃ films were grown which exhibit homogeneous and columnar grain structures with the <c > -polar axis normal to the substrate surface.     

Phase stability and non-stoichiometry in M-phase solid solutions in the system LiO0.5-NbO2.5-TiO2

Phase relations at 1050°C have been determined for M-phase solid solutions in the LiO_0.5-NbO_2.5-TiO₂ ternary phase system by the quench method. Rietveld analysis has been used to help determine phase boundaries and to study structure composition relations. The M-phases have trigonal structures based on intergrowth of corundum-like layers, [Ti₂O₃]²⁺, with slabs of (N−1) layers of LiNbO₃-type parallel to (0001). Ideal compositions are defined along the pseudobinary join LiNbO₃-Li₄Ti₅O₁₂ by the homologous series formula Li_NNb_N−4Ti₅O_3N, N?4. Homologues with N?10 lie to the low-lithia side of the LiNbO₃-Li₄Ti₅O₁₂ join and show extended single-phase solid solution ranges separated by two-phase regions. The composition variations along the solid solutions are controlled by a major substitution mechanism, Li⁺+3Nb⁵⁺↔4Ti⁴⁺, coupled with a minor substitution 4Li⁺↔Ti⁴⁺+3□, where □=vacancy. The latter substitution results in increasing deviations from the stoichiometric compositions A_2N+1O_3N with increasing Ti substitution. The non-stoichiometry can be reduced by re-equilibration at lower temperatures. Expressions have been developed to describe the compositional changes along the solid solutions.     

The structure and properties of Li1−xHxNbO3

The properties of Li_1−xH_xNbO₃ have been studied as a function of x, temperature, and stoichiometry of the LiNbO₃ used for its preparation. X-ray diffraction, thermal analysis measurements, and infrared spectroscopy have been used. The intent of this study was to gain a deeper understanding of the basic properties of this material, which has potential importance as a waveguide material in LiNbO₃ optical devices. An approximate phase diagram was constructed for the stoichiometric LiNbO₃HNbO₃ system. In one concentration range (0.56 ≤ x ≤ 0.75), particularly complex structural behavior was found: depending on x, samples undergo one, two, or three phase transitions with temperature, and the system appears to exhibit critical behavior. Samples made by proton exchange of congruent LiNbO₃ ([Li₂O]_0.486[Nb₂O₅]_0.514) show generally similar structural chemistry, with one exception: a new monoclinic phase, isomorphous with MnF₃, was found for 0.75 ≤ x ≤ 0.77. Possible reasons for the refractive index changes caused by proton exchange are discussed.     

Synthesis of nanosized (Li,La){Ti,Nb,Ta}O3 particles using the sol-gel method

Nanoparticles of lithium titanate, niobate, and tantalate with the structure of defect perovskite were synthesized using the Pechini method. The formation of single-phase lithium lanthanum titanate was shown to occur at 700°C. The average particle size was d ～ 15 nm. For niobate and tantalate, the formation of the perovskite phase started at 900°C; the average particle size in this case was 50–100 nm.