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.     

A study of the formation of LiNbO3 in the system Li2CO3Nb2O5

The formation process of LiNbO₃ in the system Li₂CO₃Nb₂O₅ was discussed from the results of non-isothermal or isothermal TG experiments and X-ray analysis. The mixture Li₂CO₃ and Nb₂O₅ in mole ratios of 1:3, 1:1 or 3:1 was heated at a rate of 5°C min^?1 or at various temperatures fixed in the range 475 to 677°C. If the system has a composition of Li₂CO₃ + 3Nb₂O₅ or 3Li₂CO₃ + Nb₂O₅, the reaction between Li₂CO₃ and Nb₂O₅ proceeds with CO₂ evolution to form LiNbO₃ at ca. 300–600°C, but Nb₂O₅ or Li₂CO₃ remains unreacted. A composition of Li₂CO₃ + Nb₂O₅ gives LiNbO₃ at 300–700°C. The diffusion of Li₂O through the layer of LiNbO₃ is rate-controlling with an activation energy of 51 kcal mol^?1. The reaction between LiNbO₃ and Nb₂O₅ gives LiNb₃O₈ at 600–700°C. At 700–800°C, a slight formation of Li₃NbO₄ occurs by the reaction between LiNbO₃ and Li₂O at the outer surface of LiNbO₃ and the Li₂O component of Li₃NbO₄ diffuses toward the boundary of the LiNb₃O₈ layer through the LiNbO₃ layer. The single phase of LiNbO₃ is formed above 850°C.     

Sol–gel niobia sorbent with a positively charged octadecyl ligand providing enhanced enrichment of nucleotides and organophosphorus pesticides in capillary microextraction for online HPLC analysis

A niobia‐based sol–gel organic–inorganic hybrid sorbent carrying a positively charged C₁₈ ligand (Nb₂O₅‐C₁₈(+ve)) was synthesized to achieve enhanced enrichment capability in capillary microextraction of organophosphorus compounds (which include organophosphorus pesticides and nucleotides) before their online analysis by high‐performance liquid chromatography. The sorbent was designed to simultaneously provide three different types of molecular level interactions: electrostatic, Lewis acid–base, and van der Waals interactions. To understand relative contributions of various molecular level analyte–sorbent interactions in the extraction process, two other sol–gel niobia sorbents were also created: (a) a purely inorganic sol–gel niobia sorbent (Nb₂O₅) and (b) an organic–inorganic hybrid sol–gel niobia sorbent carrying an electrically neutral‐bonded octadecyl ligand (Nb₂O₅‐C₁₈). The extraction efficiency of the created sol–gel niobia sorbent (Nb₂O₅‐C₁₈ (+ve)) was compared with that of analogously designed and synthesized titania‐based sol–gel sorbent (TiO₂‐C₁₈ (+ve)), taking into consideration that titania‐based sorbents present state‐of‐the‐art extraction media for organophosphorus compounds. In capillary microextraction with high‐performance liquid chromatography analysis, Nb₂O₅‐C₁₈ (+ve) had shown 40–50% higher specific extraction values (a measure of extraction efficiency) over that of TiO₂‐C₁₈ (+ve). Compared to TiO₂‐C₁₈(+ve), Nb₂O₅‐C₁₈(+ve) also provided superior analyte desorption efficiency (96 vs. 90%) during the online release of the extracted organophosphorus pesticides from the sorbent coating in the capillary microextraction capillary to the chromatographic column using reversed‐phase high‐performance liquid chromatography mobile phase.     

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.     

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.     

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.     

Solid state reactions in the system Nb2O5·WO3: An electron microscopic study

Lattice imaging electron microscopy has been used to study the mechanism of solid state reactions of the type: A_s → B_s + C_s, in which the product B is able to intergrow coherently with the starting material A, but the product C cannot do so. C must be formed by a fully reconstructive, heterogeneous process; formation of B is only partially reconstructive, and essentially homogeneous. Reactions were the reversible phase reactions in the system Nb₂O₅WO₃: disproportionation of the (5 × 4)₁ block structures of 8Nb₂O_5·5WO₃, to form (4 × 4)₁ blocks of 7Nb₂O_5·3WO₃ as coherent product, and that of 9Nb₂O_5·8WO₃ (with (5 × 5)₁ blocks), forming (5 × 4)₁ blocks of 8Nb₂O_5·5WO₃ as coherent product. The coherent product structure is formed in isolated rows of blocks, or small packets of such rows, running across each crystal. The reaction does not work in progressively from some surface initiating step, with an interface between unchanged and converted material, but represents a block-by-block conversion, linearly propagated. Nb₂O₅ and WO₃ must be abstracted, in appropriate stoichiometric ratio, from each block but must ultimately reach and react at the surface, to form the incoherent product (a pentagonal tunnel network structure, in both cases). Some homogeneous transport process involving lattice diffusion must be invoked. Domains of highly anomalous structure, regarded as relicts of transient conditions, are occasionally observed. From reactions at relatively low temperatures, these have structures that can be regarded as partially ordered nonstoichiometric solid solutions; after prolonged heating, and at higher temperatures they form well ordered strips of metastable block structures. Both types represent strong, spontaneous fluctuations of composition, which impose a corresponding structure locally. These fluctuations may be associated with the transport of WO₃ and Nb₂O₅ away from the locus of reaction. Evidence about the mechanism of the reactions, the role of dislocations and the nature of cooperative processes is considered.     

Etude des propriétés cristallographiques,diélectriques et d'optique non linéaire de quelques nouvelles phases de composition BaxLi5−2xNb5(1−y)Ta5yO15 et de structure bronzes oxygénés de tungstène quadratiques

Two series of phases with tetragonal bronze-like structure and composition Ba_xLi_5?2xT₅O₁₅ (T = Nb, Ta) have been isolated in the systems BaNb₂O₆LiNbO₃ and BaTa₂O₆LiTaO₃. All these phases show ferroelectric-paraelectric transitions. The Curie temperature increases with the lithium content. The value of T_C for Ba_2.03Li_0.94Nb₅O₁₅ is the highest ever observed for this type of structure: the obtained phases are potentially good materials for the harmonic generation of the 0.53-μm radiation. The optical yield of the niobate Ba_2.14Li_0.71Nb₅O₁₅ is about 2.5 times that of Ba₂NaNb₅O₁₅ and 250 times that of the K.D.P. The crystallographic and dielectric data of the system Ba_2.14Li_0.71Nb₅O₁₅Ba_2.14Li_0.71Ta₅O₁₅ characterize three domains, which are respectively antiferroelectric, ferroelectric, and paraelectric. The Curie temperature and the optical yield decrease with increasing tantalum content.     

Thermal Ethane Activation by Bare [V2O5]+ and [Nb2O5]+ Cluster Cations: on the Origin of Their Different Reactivities

The gas‐phase reactivity of [V₂O₅]⁺ and [Nb₂O₅]⁺ towards ethane has been investigated by means of mass spectrometry and density functional theory (DFT) calculations. The two metal oxides give rise to the formation of quite different reaction products; for example, the direct room‐temperature conversions C₂H₆→C₂H₅OH or C₂H₆→CH₃CHO are brought about solely by [V₂O₅]⁺. In distinct contrast, for the couple [Nb₂O₅]⁺/C₂H₆, one observes only single and double hydrogen‐atom abstraction from the hydrocarbon. DFT calculations reveal that different modes of attack in the initial phase of C?H bond activation together with quite different bond‐dissociation energies of the M?O bonds cause the rather varying reactivities of [V₂O₅]⁺ and [Nb₂O₅]⁺ towards ethane. The gas‐phase generation of acetaldehyde from ethane by bare [V₂O₅]⁺ may provide mechanistic insight in the related vanadium‐catalyzed large‐scale process.     

A Stable,Non‐Corrosive Perfluorinated Pinacolatoborate Mg Electrolyte for Rechargeable Mg Batteries

Mg batteries are a promising energy storage system because of the physicochemical merits of Mg as an anode material. However, the lack of electrochemically and chemically stable Mg electrolytes impedes the development of Mg batteries. In this study, a newly designed chloride‐free Mg perfluorinated pinacolatoborate, Mg[B(O₂C₂(CF₃)₄)₂]₂ (abbreviated as Mg‐FPB ), was synthesized by a convenient method from commercially available reagents and fully characterized. The Mg‐FPB electrolyte delivered outstanding electrochemical performance, specifically, 95 % Coulombic efficiency and 197 mV overpotential, enabling reversible Mg deposition, and an anodic stability of up to 4.0 V vs. Mg. The Mg‐FPB electrolyte was applied to assemble a high voltage, rechargeable Mg/MnO₂ battery with a discharge capacity of 150 mAh g^?1.     

Preferential growth orientation of laser-patterned LiNbO3 crystals in lithium niobium silicate glass

Dots and lines consisting of LiNbO₃ crystals are patterned on the surface of 1CuO-40Li₂O-32Nb₂O₅-28SiO₂ (mole ratio) glass by irradiations of continuous-wave Nd:YAG laser (wavelength: λ=1064 nm), diode laser (λ=795 nm), and Yb:YVO₄ fiber laser (λ=1080 nm), and the feature of laser-patterned LiNbO₃ crystal growth is examined from linearly polarized micro-Raman scattering spectrum measurements. LiNbO₃ crystals with the c-axis orientation are formed at the edge parts of the surface and cross-section of dots. The growth direction of an LiNbO₃ along the laser scanning direction is the c-axis. It is proposed that the profile of the temperature distribution in the laser-irradiated region and its change along laser scanning would be one of the most important conditions for the patterning of crystals with a preferential growth orientation. Laser irradiation giving a narrow width is also proposed to be one of the important factors for the patterning of LiNbO₃ crystal lines with homogeneous surface morphologies.     

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.     

A Stable,Non‐Corrosive Perfluorinated Pinacolatoborate Mg Electrolyte for Rechargeable Mg Batteries

Mg batteries are a promising energy storage system because of the physicochemical merits of Mg as an anode material. However, the lack of electrochemically and chemically stable Mg electrolytes impedes the development of Mg batteries. In this study, a newly designed chloride‐free Mg perfluorinated pinacolatoborate, Mg[B(O₂C₂(CF₃)₄)₂]₂ (abbreviated as Mg‐FPB ), was synthesized by a convenient method from commercially available reagents and fully characterized. The Mg‐FPB electrolyte delivered outstanding electrochemical performance, specifically, 95 % Coulombic efficiency and 197 mV overpotential, enabling reversible Mg deposition, and an anodic stability of up to 4.0 V vs. Mg. The Mg‐FPB electrolyte was applied to assemble a high voltage, rechargeable Mg/MnO₂ battery with a discharge capacity of 150 mAh g^?1.     

Coupled TG-MS study on the intermediate for formation of PbO(t) from PbO(O) in synthesis of perovskite PMN-PT

Pb(OH)₂ was previously proposed as an intermediate in the synthesis of PMN [Pb(Mg_1/3Nb_2/3)O₃] and PMN-PT [0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃] from a mixture of PbO, Nb₂O₅, Mg(NO₃)₂·6H₂O (w/w₀) TiO₂ by the modified mixed oxide method based on TG/DSC and XRD data. Coupled TG-MS of the precursor reveals that the intermediate is Pb₆O₅(NO₃)₂, not Pb(OH)₂ because the evolved gas was nitric oxide and oxygen, not water.     

Thermal decomposition of lithium-inserted NbO2F

The thermal decomposition of lithium-inserted NbO₂F was studied by differential scanning calorimetry. Samples of Li_xNbO₂F (O ⩽ x ⩽ 1.8) were heated to 800 and 950 K. The thermograms revealed that decomposition started within the temperature range 640–780 K followed by a second step at approximately 900 K. The products were characterized by X-ray powder diffraction and electron diffraction patterns and by high resolution electron microscopy. The following phases were obtained at 800 K: LiF, NbO₂F, the low pressure form of Nb₃O₇F, and lithium-enriched forms of PNb₂O₅, NbO₂ and LiNbO₃. At 950 K, NbO₂F disappeared, and LiNb₃O₈ and the high pressure form of Nb₃O₇F coexisted with the other phases obtained at 800 K. The formation of structures built up of approximately hexagonally close-packed anion arrangements is discussed, as well as the role of lithium as a stabilizing component.     

Eine neue Kristallstruktur des Nickel-Oxoniobats: II-Ni4Nb2O9

A New Crystal Structure of the Nickel-Oxoniobate: II-Ni₄Nb₂O₉ A new crystal structure of Ni₄Nb₂O₉ was examined by X-ray data. II-Ni₄Nb₂O₉ crystallizes with orthorhombic symmetry (space group C–Pcan; a = 5.0545, b = 8.7688, c = 14.3041 Å, Z = 4). All the isolated single crystals are trillinged, explaining the formerly examinations with two times larger cell dimensions. The structure of II-Ni₄Nb₂O₉ is different from the well known compound I-Ni₄Nb₂O₉. The crystal chemistry in respect to other A₄M₂O₉ compounds are discussed.     

Über ein Oxotantalat mit teilgeordneter Korundstruktur: Mn0,6Mg3,4Ta2O9

About an Oxotantalate with Partly Ordered Corundum-Structure: Mn_0.6Mg_3.4Ta₂O₉ In the system of mixed crystals of the composition Mn_4?xMg_xTa₂O₉ single crystals with x = 3.4 were examined by X-ray methods (space group D–P3 c1; a = 5.2141; c = 14.178 Å; Z = 2). The point positions of the divalent metals are occupied in an ordered manner. Order and disorder are discussed in respect to Mn₂Zn₂Nb₂O₉, Mn₃ZnNb₂O₉, and oxotantalates (MM′)₄Ta₂O₉ [M, M′ = Zn, Ni, Mg].     

Formation of MgxNbyOx+y through the Mechanochemical Reaction of MgH2 and Nb2O5, and Its Effect on the Hydrogen‐Storage Behavior of MgH2

The present study aims to understand the catalysis of the MgH₂–Nb₂O₅ hydrogen storage system. To clarify the chemical interaction between MgH₂ and Nb₂O₅, the mechanochemical reaction products of a composite mixture of MgH₂+0.167 Nb₂O₅ was monitored at different time intervals (2, 5, 15, 30, and 45 min, as well as 1, 2, 5, 10, 15, 20, 25, and 30 h). The study confirms the formation of catalytically active Nb‐doped MgO nanoparticles (typically Mg_xNb_yO_x+y, with a crystallite size of 4–8 nm) by transforming reactants through an intermediate phase typified by Mg_m?xNb_2n?yO_5n?(x+y). The initially formed Mg_xNb_yO_x+y product is shown to be Nb rich, with the concentration of Mg increasing upon increasing milling time. The nanoscale end‐product Mg_xNb_yO_x+y closely resembles the crystallographic features of MgO, but with at least a 1–4 % higher unit cell volume. Unlike MgO, which is known to passivate the surfaces in MgH₂ system, the Nb‐dissolved MgO effectively mediates the Mg–H₂ sorption reaction in the system. We believe that this observation will lead to new developments in the area of catalysis for metal–gas interactions.     

Compound and solid-solution formation in the system Li2ONb2O5TiO2

A systematic study of compound and solid-solution formation in the system Li₂ONb₂O₅TiO₂ has been made. Several solid-solution series, based on LiNbO₃, LiNb₃O₈, Li₂Nb₂₈O₇₁, Li₂TiO₃, phase M, Li₂Ti₃O₇, and TiO₂, have been characterized. In all cases, the principal solid-solution mechanism appears to involve stoichiometric formulae with constant overall cation content. One new phase, of approximate formula Li₁₃TiNb₅O₂₁, has been prepared. A subsolidus phase diagram for the ternary system is presented.