Pure Crystalline Phase Research Articles

Decay emission study of ZnO nanostructures obtained by low-pressure vapor transport technique

Currently, the search for inexpensive, non-toxic, and environmentally friendly materials for optoelectronic applications has led to an increased interest in one-dimensional ZnO materials. Attributes such as their high surface area, crystalline phase purity, and high photoexcited response make them attractive for light emission, biosensing, and energy harvesting applications. However, there is still a need for studies that correlate the optical and structural properties of these materials, so they can be integrated as functional building blocks in practical devices. In this work, we report the growth of 1D ZnO nanostructured films using a low-pressure vapor transport technique. Gold-plated substrates allowed us to achieve different types of homogeneous films composed of nanowires/nanorods. Through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-Ray diffraction (XRD) the high-crystalline structure and morphological properties of the materials were determined. The presented methodology also offers control over the growth direction of the nanostructures, as both random and highly aligned matrixes were obtained. Finally, the optical properties of the system were studied by photoluminescence spectroscopy (PL). Along with the excitonic emission, a significant role of defect-related luminescence was found, allowing us to interpret the emission mechanism for the different morphologies of ZnO nanostructures. Time-resolved PL experiments determined decays between 1.9-0.3 ns where an enhancement in the carrier's lifetime was observed as the size of the nanostructure increased. The present study could help us to design efficient ZnO nanostructures with control over their morphology and controllable optoelectronic properties for modern device fabrication.

Thermal sensitivity of the Nd3+/Yb3+ co-doped β-BaB2O4 nanoparticles for luminescence nanothermometry

In this work, the synthesis and characterization of the β-BaB2O4 (β-BBO) phase single-doped with Nd3+ and co-doped with Nd3+/Yb3+ were performed. This work focuses on luminescence nanothermometry application in the near-infrared (NIR) window and the temperature range between 25 and 55 °C to evaluate potential technological applications in nanomedicine. The polymeric precursor method was used for the synthesis of Nd3+ doped and Nd3+/Yb3+ co-doped β-BBO nanoparticles (0.2 mol% of each doping ion) crystallized after a heat-treatment. The structural and thermal properties of these nanoparticles were characterized using thermal analysis (Thermogravimetry and Differential Scanning Calorimetry) to specify the temperature of heat treatment (20 h at 750 °C) for the formation of pure crystalline phases characterized by X-ray diffraction and Raman spectroscopy. Transmission Electron Microscopy was used to assess the shape (parallelepiped needles) of the particles, their length (∼214 nm) and average width (∼18 nm), as well as the orientation of the atomic planes of the crystalline planes by electron diffraction. Diffuse reflectance spectroscopy allowed to specify the transparency range of the pure crystalline matrix and to investigate the absorption bands of the doping ions, as well as to determine the bandgap using the Kubelka-Munk equation. In addition, the temperature dependence of the luminescence intensity ratios of Stark components from both Nd3+ and Yb3+ ions were analyzed. This led to a relative thermal sensitivity value of 0.06%·oC−1 for single-doped Nd3+ sample and 0.23%·oC−1 for Nd3+/Yb3+ co-doped sample from emissions in the range 1050.5 nm–1067.5 nm. Finally, a value of 0.28%·oC−1 was found for Nd3+/Yb3+ co-doped sample from the intensity ratio between emissions at 979.0 nm and 1058.5 nm. Thus, the relative thermal sensitivity of the β-BBO phase co-doped with the ions Nd3+ and Yb3+ at the concentration of 0.2 mol.% was superior to that of some matrices found in the literature. This allows us to conclude that Nd3+/Yb3+ co-doped β–BBO nanoparticles can be used as an efficient luminescent nanothermometer in the near-infrared.

Morphology‐controlled synthesis and structural features of ultrafine nanoparticles of Co3O4: An active electrode material for a supercapacitor

AbstractIn this study, the authors present a morphology‐controlled synthesis strategy for the preparation of Co3O4 nanoparticles. The importance of the fuel (ascorbic acid) to oxidiser (cobalt nitrate) ratio (F/O ratio) in obtaining evenly distributed nanoscale grain Co3O4 with pure crystalline phases using the solution combustion method is proposed. The structural features of all the as‐formed cobalt oxide nanoparticles were studied using the powder X‐ray diffraction technique, a field emission scanning electron microscope and Raman spectroscopic techniques. The electrochemical characteristics of all the as‐formed cobalt oxide nanoparticle‐embedded electrodes were examined by cyclic voltammetry, galvanostatic charge–discharge studies and electrochemical impedance spectroscopy in a 2 M KOH solution. The electrochemical data demonstrated that the Co3O4 nanoparticles showed good capacitive behaviour. The morphological changes in the Co3O4 nanoparticles affect the charge storage mechanism, and Co3O4 nanoparticles with an F/O ratio equal to 1 (COO2) showed the highest electrochemical property, with a specific capacitance of 166 F g−1 at a current density 0.5 A g−1. The COO2 electrode material showed capacitance retention of 90% after 5000 cycles.

High-Entropy Spinel Oxides Produced via Sol-Gel and Electrospinning and Their Evaluation as Anodes in Li-Ion Batteries

In the last few years, high-entropy oxides (HEOs), a new class of single-phase solid solution materials, have attracted growing interest in both academic research and industry for their great potential in a broad range of applications. This work investigates the possibility of producing pure single-phase HEOs with spinel structure (HESOs) under milder conditions (shorter heat treatments at lower temperatures) than standard solid-state techniques, thus reducing the environmental impact. For this purpose, a large set of HESOs was prepared via sol-gel and electrospinning (by using two different polymers). Ten different equimolar combinations of five metals were considered, and the influence of the synthesis method and conditions on the microstructure, morphology and crystalline phase purity of the produced HESOs was investigated by a combination of characterization techniques. On the other hand, the presence of specific metals, such as copper, lead to the formation of minority secondary phase(s). Finally, two representative pure single-phase HESOs were preliminarily evaluated as active anode materials in lithium-ion batteries and possible strategies to enhance their rate capability and cyclability were proposed and successfully implemented. The approaches introduced here can be extensively applied for the optimization of HEO properties targeting different applications.

Green Fuel Production from Sunflower Oil Using Nanocatalysts Based on Metal Oxides (SrO, La2O3, CaO, MgO, Li2O) Supported over Combustion‐synthesized Mg-spinel

In this research a series of metal oxides (SrO, La2O3, CaO, MgO, and Li2O) were loaded over Mg-spinels via a hybrid combustion-impregnation method. Nanocatalysts were characterized by XRD, FESEM, TEM, EDX, BET-BJH, and FTIR analyses. The XRD results showed the formation of pure crystalline phases in all of the nanocatalysts. Among all the nanocatalysts, the FESEM images and BET-BJH data displayed large pore diameters and high specific surface area for Li2O/MgAl2O4. Also, the overview of 3D surface analysis demonstrated the rough surface for this nanocatalyst, in which the RMS parameter was evaluated to be 16.5 nm. The as-prepared nanocatalysts were successfully employed in green biodiesel production from sunflower oil (MeOH/Oil = 12 molar, catalyst loading = 5 wt%, temperature = 110 °C and time = 3 h). The superior activity of about 98% was obtained with Li2O/MgAl2O4. The other remarkable outcome of this research was the reusability of Li2O/MgAl2O4 through 6 reaction cycles with fresh feed in the same operational conditions.

Deep Eutectic Solvent Synthesis of Perovskite Electrocatalysts for Water Oxidation.

Oxide perovskites have attracted great interest as materials for energy conversion due to their stability and structural tunability. La-based perovskites of 3d-transition metals have demonstrated excellent activities as electrocatalysts in water oxidation. Herein, we report the synthesis route to La-based perovskites using an environmentally friendly deep eutectic solvent (DES) consisting of choline chloride and malonic acid. The DES route affords phase-pure crystalline materials on a gram scale and results in perovskites with high electrocatalytic activity for oxygen evolution reaction. A convenient, fast, and scalable synthesis proceeds via assisted metathesis at a lower temperature as compared to traditional solid-state methods. Among LaCoO3, LaMn0.5Ni0.5O3, and LaMnO3 perovskites prepared via the DES route, LaCoO3 was established to be the best-performing electrocatalyst for water oxidation in alkaline medium at 0.25 mg cm–2 mass loading. LaCoO3 exhibits current densities of 10, 50, and 100 mA cm–2 at respective overpotentials of approximately 390, 430, and 470 mV, respectively, and features a Tafel slope of 55.8 mV dec–1. The high activity of LaCoO3 as compared to the other prepared perovskites is attributed to the high concentration of oxygen vacancies in the LaCoO3 lattice, as observed by high-resolution transmission electron microscopy. An intrinsically high concentration of O vacancies in the LaCoO3 synthesized via the DES route is ascribed to the reducing atmosphere attained upon thermal decomposition of the DES components. These findings will contribute to the preparation of highly active perovskites for various energy applications.

Hydrothermal synthesis and characterization of undoped and W-doped vanadium dioxide nanorods for thermochromic application

Owing to vanadium dioxide’s semiconductor to metal transition near room temperature, it is an ideal candidate for thermochromic applications. In this paper, we report the synthesis of undoped and W-doped vanadium dioxide (VO2) nanorods using hydrothermal method. VO2 (B) was synthesized via a hydrothermal reaction from vanadium pentoxide (V2O5) and oxalic acid dihydrate (H2C2O4·2H2O). VO2 (B) transformed to VO2 (M) after annealing at 500°C under vacuum. The structure and morphology of the synthesised nanorods were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). For the (011) peak, the XRD patterns of undoped VO2 nanorods powder showed a highly crystalline pure monoclinic phase. The X-ray diffraction patterns of the samples show a decrease in the intensity and shift slightly toward the direction of the small reflection angle when increasing W-content. According to the SEM results, the nanorods produced have length ranging from 356 to 790 nm, and the width ranges from 51 to 217 nm.

A comprehensive study on the photocatalytic activity of CuO-doped ZrO2–ZnO nanocomposites under visible light

The present work aims at synthesizing CuO-doped ZrO2–ZnO (ZZC) nanocomposites through sol-gel approach under ultrasound condition. The photocatalytic degradation of the basic red 46 (BR46, as a water pollution model) was investigated by ZZC nanocomposites under light-emitting diode (LED) visible irradiation. The characterization of the samples was carried out using instruments such as XRD, FTIR, SEM, TEM, EDAX, BET and DRS. X-ray powder diffraction results confirmed crystal structures and pure crystalline phase formation for the synthesized nanocomposites. The SEM results revealed the nanostructure of the particles. Besides, adding CuO to ZrO2–ZnO nanoparticle would lead to a consistent increase of the ZrO2–ZnO band at 405 nm with a red shift to 440 nm. A valuable model to predict behavior, optimization and simulation of purification process was developed by response surface methodology (RSM) and artificial neural network (ANN). The BR46 photocatalytic degradation of 85.32 ± 1.75% under LED visible light radiation of 18 W –obtained experimentally at optimized conditions (time 120 min, catalyst loading 25 mg/L, pH 11 and BR46 concentration 5 mg/L) –was comparable to 84.07% and 85.69% resulted from RSM and ANN, respectively.

Controlled growth of Bi-Functional La doped CeO2 nanorods for photocatalytic H2 production and supercapacitor applications

The rapid increase in energy consumption has severely rehabilitated human life urging to develop reliable and environmental friendly energy storage devices. Target oriented, systematic approach has been adopted to synthesis La doped CeO 2 nanostructures with percentage as La x Ce 1-x O 2 (X = 0,1,3,5,7) for potential super capacitors applications. Morphological doping impact on H 2 production, electrochemical and optical properties are thoroughly investigated. XRD studies revealed the crystalline phase purity and attained approximately 35 nm average crystallite size. The SEM images exposed that primary morphology nano-particles has been tuned into nanorods by increasing the La concentration in CeO 2 with size range 40∼60 nm. CV graphs depicted that the prepared electrodes obey the pseudo capacitive faradaic reactions behavior in nature. Maximum capacitance (925 F g -1 ) has been achieved by La 0·05 Ce 0·95 O 2 which is better than numerous reported materials. The La 0·05 Ce 0·95 O 2 also exhibited excellent GCD stability with 87.8% retention exhibiting it suitability for supercapacitor applications. Furthermore, the La 0·05 Ce 0·95 O 2 showed the significantly higher H 2 (9 μmol h −1 g −1 ) production rate as compared to undoped CeO 2 and La 0·01 Ce 0·99 O 2, La 0·03 Ce 0·97 O 2 samples. This higher production is attributed to the recombination rate and have strong substantial correlation with optical characteristics. • La doped CeO 2 nanorods successfully synthesized by hydrothermal method. • Specific capacitance 925 F g -1 has been achieved for La 0·05 Ce 0·95 O 2 nanorods. • More than 87% cyclic stability was achieved for La 0·05 Ce 0·95 O 2 nanorods. • The La 0·05 Ce 0·95 O 2 showed the significantly H 2 production rate (9 μmol h −1 g −1 ).

Comparative study on the effect of synthesis route on the structural, magnetic, and magnetocaloric properties of La0 .5Ca0.5Mn0.95V0.05O3 manganite

ABSTRACT The influence of the synthesis method on structural, magnetic and magnetocaloric properties of the La0.5Ca0.5Mn0.95V0.05O3 compound has been investigated. The compound was prepared by glycine nitrate process (GNP) and compared to counterparts obtained with solid-state route (S-S) and ball milling (B-M). The structural analysis shows a pure and single-orthorhombic crystalline phase for the GNP compound. A secondary phase LaVO4 was detected for S-S and B-M samples. From magnetization versus temperature analysis, different magnetic behaviors were distinguished when moving from one technique to another. The nature of transition was determined and a crossover from second order to first-order magnetic transition was observed with the decrease of crystallite size. Landau theory was performed to confirm the order of magnetic transition of the sample consistent with the Banerjee criterion. The magnetic entropy change (ΔSm) and the relative cooling power RCP, which decreased by reducing the particle size, were calculated.

Analysis and evaluation of structural properties of Co3O4 microparticles obtained at low temperature

In the present research, the synthesis of cobalt oxide Co3O4 was carried out using the sol-gel technique with subsequent heat treatment at 225 and 235 °C. The final product obtained was characterized by X-ray diffraction (XRD), showing a pure crystalline phase of Co3O4, cell parameters a=b=c=8.071 Å, and a volume of 525.7 Å3. The particle size was between 2.37 and 2.77 µm, which indicated that structural transformations from Co to Co3O4 induced an increase in the particle size. Through Rietveld refinement, the interatomic distances and inclination angles of the Co1, Co2, and Co3 polyhedra were analyzed in order to establish the structural behavior of cobalt oxide (II, III) at 235 °C. The UV-vis analysis allowed determining band gap (Eg) with values of 1.6 eV in the first region and 0.97 eV in the second. Scanning electron microscopy images showed that the particles agglomerated with increasing calcination temperature and exhibited larger particles. This work presents a detailed analysis of structural parameters of Co3O4 using the Vesta software with Rietveld refinement data.

Modifying HKUST-1 Crystals for Selective Ethane Adsorption Using Ionic Liquids as Synthesis Media

Novel adsorbents for methane and ethane based on HKUST-1 metal-organic framework were synthesized by microwave (MW) assisted technique using ionic liquids (ILs) as synthesis media. It was found that the MW synthesis time remarkably impacts both the product yield and the physico-chemical characteristics of the produced HKUST-1 material. The crystalline phase purity, crystallite size/dispersion and textural properties of the synthesized HKUST-1 matrices determine their performance in methane and ethane adsorption. Therefore, the HKUST-1 material produced in MW fields for 3 min only shows the highest phase purity and the largest surface area (BET) and porosity, along with a rather small crystallite size (below ~300 nm), demonstrating high methane and ethane adsorption capacity in the pressure range 1–30 atm.

Nitriding improvement of luminescence properties and energy-transfer behaviors of LaMgAl11-xSi3x/4O19-3x/2Nx:0.55Ce3+ 0.25 Tb3+ phosphors for UV- light pumping lamps

The green emitting phosphors with general formula (La,Ce,Tb)MgAl11-xSi3x/4O19-3x/2Nx (0 ≤ x ≤ 0.5) were prepared with high temperature solid state reaction in reducing atmosphere with composition 95%N2–5%H2. Co-doping with Si3N4 suppressed formation of secondary phase, and all samples showed pure crystalline LaMgAl11O19 phase. The La0.2MgAl11-xSi3x/4O19-3x/2Nx: 0.55Ce3+, 0.25 Tb3+ sample showed typical green emission related to the 5D4 to 7F5 transition of Tb ions, which was observed under 282 nm excitation owing to Ce–Tb transfer. Doping with nitrogen reduced the distance between Ce and Tb ions, which resulted in the improved luminescence as compared with undoped samples. Existing vacancy states reflected strongly in thermal dependence of luminescence of investigated phosphors. Finally, the luminous efficiency of lamps made of nitrided phosphors under ultraviolet excitation is higher than that of lamps without nitrogen-doped phosphors. This proves that doping with nitrogen is feasible way to improve luminous efficacies of currently commercially available phosphors.

Green synthesis of gold nanaoparticles using Delphinium Chitralense tuber extracts, their characterization and enzyme inhibitory potential.

Green synthesis has been introduced as an alternative to chemical synthesis due to the serious consequences. Metal nanoparticles synthesized through green approach have different pharmaceutical, medical and agricultural applications. The present study followed a green and simple route for the preparation of potentially bioactive gold nanoparticles (Au NPs). Au NPs were prepared via green synthesis approach using crude basic alkaloidal portion of the tuber of Delphinium chitralense. The green synthesized Au NPs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) fourier transform infrared (FTIR), and UV-Visible spectrophotometer. Morphological analysis shows that Au NPs have cubic geometry with different sizes. UV-Vis spectroscopic analysis confirmed the synthesis of Au NPs while XRD proved their pure crystalline phase. The Au NPs showed promising dose dependent inhibition of both AChE and BChE as compared to the crude as well as standard drug.

Efficient, scalable, closed-loop synthesis of highly crystalline pure phase MgAl-layered double hydroxides intercalated with hydroxyl anions.

Layered double hydroxides (LDHs) can play an important role in various areas, but conventional LDHs synthesis often causes product agglomeration and generates plenty of high-salt wastewater, and requires a time-consuming aging process to reach the desired purity and crystalline state. Herein, we report the synthesis of MgAl-LDH, a representative of these kinds of ionic lamellar inorganic solids, with a novel method involving the reaction of magnesium oxide (MgO) with aluminate ions (Al(OH)4-) in a strongly alkaline environment. The formation of MgAl-LDH follows a mechanism of interfacial dissolution-reprecipitation (IDR), i.e., Mg2+ ions released at the interface of dissolved MgO react immediately with Al(OH)4- ions to reprecipitate as MgAl-LDH. The obtained MgAl-LDH has no impurity phases and shows high crystallinity, high specific surface area, and a narrow particle size distribution. Moreover, MgAl-LDH is intercalated with OH- anions, so it can be directly used as a Brønsted base catalyst and ion exchanger. The novel method requires no time-consuming aging process and is highly scalable. It is also shown that a closed-loop synthesis of MgAl-LDH without waste discharge can be achieved with an appropriate Al source, e.g., Al(OH)3, and a recycled NaOH solution.

Magnetic assisted synthesis of ZnO nanoparticle by electrochemical discharge method

Metal oxide optoelectronics nanoparticles are widely used in industries. Many efforts were made to form uniform and pure metal oxide Nanoparticles. This paper focused on synthesizing simple step nanoflower like ZnO structure in atmospheric conditions. The Electrochemical discharge method is used to synthesize ZnO nanoparticles in NaOH electrolyte medium. The effect of electrolyte rotation on morphology was analyzed at 200 rpm resulted uniform flower shape of nanoparticles, confirmed by FESEM images. The XRD results reveal that the pure crystalline phase of nanoparticles obtained has the average crystalline size of 29 nm. The uniform voltage and current wave form was also observed at 200 rpm rotation of electrolyte. The chemical composition of the element was studied by EDS analysis to confirm the presence of zinc and oxygen element. DLS result gives the hydrodynamic diameter of nanoparticles within the range of 100 nm.

A novel apatite-inspired Sr5(PO4)2SiO4 plasma-sprayed coating on Ti alloy promoting biomineralization, osteogenesis and angiogenesis

Osteoconductive, osteoinductive, anti-infection, and controlled ionic release properties are crucial for the long-term clinical success of orthopedic and dental metallic implants. In this study, we have successfully synthesized apatite chemical structure mimic Sr5(PO4)2SiO4 (SPS) nanopowder by sol-gel method to be used as a novel bioactive ceramics coatings on medical-grade titanium alloy by plasma-spray deposition technique. The deposited SPS coatings were analytically characterized by XRD and SEM-EDS analysis and confirmed that the coating possessed a pure crystalline phase of SPS without any other secondary phases, and exhibited a sharp needle-like morphology with the existence of Sr, P, O, Si elements. The cross-sectional view proved that the deposition of dense SPS layer with a thickness of 116 μm. The in vitro ionic dissolution behavior of SPS coatings was detected by ICP-OES analysis and confirmed their controlled releasing profile of ions such as Sr (120–55 ppm) and Si (0.14–9.86 ppm). In vitro biomineralization study demonstrated that the SPS coatings were remarkably encouraged the ball likes apatite crystals growth on their surface with a Ca/P ratio (1.677) similar to natural bone minerals. The SPS coatings exhibited notable cellular interactions with human umbilical card-derived mesenchymal stem cells (HUMSCs) in terms of cell proliferation, early-stage differentiation, and calcium nodule accumulation in ECM, also the osteogenic differentiation was found to be prominent for SPS coated Ti64 than sandblasted Ti64. Furthermore, the angiogenic property of SPS coated Ti64 was evaluated by Human umbilical vein endothelial cells (HUVECs) and confirmed their tremendous cell viability with non-toxicity and nominal angiogenic differentiation. Therefore, our study proved that the apatite-inspired SPS bioactive ceramics coatings could improve the biofunctional activities of orthopedic and dental implants for their better clinical success.

Structural and electrical studies of thermally annealed tungsten nitride thin film

Present work is focused on various properties of thermally annealed tungsten nitride (WN) film. Tungsten nitride thin films on silicon (100) substrates were deposited via reactive magnetron sputtering technique. Initially Ar/N2 flow ratio was optimized by varying N2 gas flow between 5 to 25 sccm. 20:5 (Ar:N2) was found to be the best for W2N phase formation. Using optimized condition, a set of WN deposited and then annealed at different temperatures i.e. 200°C, 400°C and 600°C for two hours each. Various characterizations have been done using X-ray diffraction, four probe resistivity and nano-indentation test. XRD results suggest formation of pure W2N crystalline phase of the films with face centered cubic structure. The resistivity result shows the decrease of resistivity value with increase in annealing temperature. Nano-indentation results showed hardness and elastic modulus values at 5mn load does not vary much with annealing at different temperatures. Structural, mechanical and electrical studies showed that the samples were stable up to 600°C. Thus, tungsten nitride thin films will contribute as a material suitable for long time exposure at elevated temperature for application of cutting tools. Copyright © 2017 VBRI Press.

LiAlO<sub>2</sub> prepared by nitrates-free synthesis for carbon capture by MCFCs

The pure crystalline phase of alpha lithium aluminate, the state-of-the-art matrix support material, was directly prepared by two nitrates-free methods at 650 °C. A solgel method included pyrolysis of a colloidal mixture of aluminum hydroxide sol and lithium formate. The advantages of the used formate pyrolysis are the absence of nitrogen oxide emission in comparison to other combustion methods as well as it provides high homogeneity of a product. The solid-state reaction is a conventional method used in industry so the optimal powder-to-ball weight ratio was found in this study to give a high surface area. Described methods of synthesis are easy, economic and low-emission methods for the preparation of submicron α-LiAlO<sub>2</sub> powders with the surface area of about 25‒27 m 2 /g which is optimal for application as matrix material in мolten сarbonate fuel cells.

Synthesis and crystal structure of bis-[μ-N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-bis-[N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-μ4-oxido-hexa-μ3-oxido-octa-μ2-oxido-tetra-oxido-tetra-nickel(II)hexa-tantalum(V) nona-deca-hydrate.

Reaction of K8{Ta6O19}·16H2O with [Ni(tren)(H2O)Cl]Cl·H2O in different solvents led to the formation of single crystals of the title compound, [Ni4Ta6O19(C6H18N4)4]·19H2O or {[Ni2(κ4-tren)(μ-κ3-tren)]2Ta6O19}·19H2O (tren is N,N-bis-(2-amino-eth-yl)-1,2-ethanediamine, C6H18N4). In its crystal structure, one Lindqvist-type anion {Ta6O19}8- (point group symmetry ) is connected to two NiII cations, with both of them coordinated by one tren ligand into discrete units. Both NiII cations are sixfold coordinated by O atoms of the anion and N atoms of the organic ligand, resulting in slightly distorted [NiON5] octa-hedra for one and [NiO3N3] octa-hedra for the other cation. These clusters are linked by inter-molecular O-H⋯O and N-H⋯O hydrogen bonding involving water mol-ecules into layers parallel to the bc plane. Some of these water mol-ecules are positionally disordered and were refined using a split model. Powder X-ray diffraction revealed that a pure crystalline phase was obtained but that on storage at room-temperature this compound decomposed because of the loss of crystal water mol-ecules.