LiNbO3 Nanoparticles Research Articles

Synthesis of LiNbO<SUB>3</SUB> Nanoparticles by Citrate Gel Method

We present investigations on the preparation of nearly stoichiometric lithium niobate (LiNbO3) nanoparticles using citrate gel method. Citric acid is used as a chelating agent and ethylene glycol is added for polyestarification between the chelates. In addition to the main lithium niobate phase, the secondary phase of lithium niobate, LiNb3O8, and an unreacted phase of Nb2O5 were also observed in the resultant product. The appearance of unwanted phases is a serious problem in citrate gel method. We have observed that the synthesis parameters such as molar ratio of citric acid to metal ions (R1), pH, molar ratio of ethylene glycol to citric acid (R2) and calcination temperature strongly influence the presence of the unwanted phases and these parameters are optimized to remove these phases. Evolution of the phase was investigated by powder XRD whereas TG/DTA was done to find out the crystallization temperature. It was observed that nearly stoichiometric and pure LiNbO3 nanoparticles can be obtained with the optimized parameters, R1 = 3, pH = 8, R2 ≥ 2 and calcination temperature = 700 degrees C. The stoichiometry of the synthesized LiNbO3 nanoparticles was investigated using Raman spectroscopy.

Enhancement in pyroelectric detection sensitivity for flexible LiNbO3/PVDF nanocomposite films by inclusion content control

The pyroelectric properties of polymer-ceramic nanocomposites of Lithium niobate/Poly (vinylidene fluoride) or LiNbO3/PVDF (abbreviated LN/PVDF) for thermal/infrared sensing applications are reported in this work. The composites are prepared by dispersing nanoparticles of LiNbO3, with particle size in the range 45–65 nm, in β-PVDF matrix at varying volume fractions, and cast in the form of flexible films by solvent-cast technique. The electro-active β-phase of PVDF is confirmed by powder X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC) analyses. The thermal properties, thermal conductivity and specific heat capacity, of the composites are determined by a photothermal technique. The prepared films have been poled in a high dc electric field, and their pyroelectric and dielectric properties measured by direct methods. From these data the pyroelectric figures of merit of the composite films have been determined and their values compared with corresponding values for pure PVDF film. The Shore hardness of the films has been measured to estimate the extent to which the flexibility of the films is affected by the addition of ceramic. Significant enhancement in pyroelectric sensitivity has been obtained with increase in volume fraction of LiNbO3 nanoparticles. However, this enhancement is at the expense of the flexibility of the composite; so one has to strike a balance between the two while selecting a suitable composition for the development of pyroelectric sensors with these materials. The results of this work provide guidelines for this selection.

Investigations on crystalline structure and optical band gap of nearly stoichiometric LiNbO3 nanoparticles

The structural and optical characteristics of nearly stoichiometric lithium niobate, LiNbO3 nanoparticles have been studied. The results are very different compared to the bulk LiNbO3 single crystals. The nanoparticles were synthesized by citrate gel method and the phase was confirmed by powder X-ray diffraction. The size and size distribution of the nanoparticles were obtained by XRD, SEM, TEM and DLS experiments. The particles were in the range of 50–200nm and most of the particles are about 100nm of size. The lattice parameters obtained from selected area electron diffraction are aH=5.213Å and cH=14.026Å for hexagonal system which are slightly larger than the other reported values (JCPDS). The optical properties were obtained from optical absorption spectroscopy in UV–vis.–NIR and IR (FTIR) range, the electronic band gap structure were determined from the fundamental absorption edge in the UV region. The indirect band gap was of 4.78eV where as the direct gap was of 6.0eV which are much larger than the other experimental values. The absorption features in the UV range indicate the discrete nature of conduction band and the allowed energy levels in the forbidden gap appeared due to surface defects.

Synthesis of cubic LiNbO3 nanoparticles and their application in vitro bioimaging

Stoichiometric LiNbO3 nanoparticles with regular rhombohedral morphology and high crystallinity were synthesized through a molten salt approach. The as-synthesized cubic LiNbO3 nanoparticles as nanoprobes for long-term imaging in vitro were investigated. The as-synthesized nanoprobes exhibit unique properties of long-term observation without photobleaching, flexibility in excitation wavelength, and excellent photostability. The biocompatibility of LiNbO3 nanoprobes was determined by in vitro assay of cytotoxicity. All the tested samples presented no obvious toxicity.

Study of temperature and size dependent elastic constant of LiNbO3 nano particles embedded in Al-metal matrix

In the present communication, temperature dependent elastic constant related to Debye temperature have been studied in LiNbO3 nano-particle embedded in Al-matrix. The size of the embedded material is considered in nano range. The nanoparticles of LiNbO3 were synthesized from chemical precipitation methods. LiNbO3 possesses hcp (hexagonal closed packing) crystal structure. Ultrasonic velocity, Grneisen parameter and acoustic coupling constant that depend on the second and third order elastic constants which are used for the determination of ultrasonic attenuation coefficient. The second and third order elastic constant were computed from deformation theory. The Debye temperature depends upon the size of the material. The change in Debye temperature was found to be maximum in smaller size particles. But it is decreased with increasing the size of the nano-particles. This is due to change in thermal expansion coefficients. The elastic constant also changes with changing the size of the nano particles. Smaller nano particles show large elastic constant but it decreases with increasing the sizes of the particles. Debye temperature not only changes by the size of the materials but also causes to change in elastic constant. The second and third elastic constants show the opposite relation with the temperature.

Preparation of LiNbO3 nanoparticles using poly(l-lysine) as a biomolecular additive

The effects of poly(l-lysine) as a biomolecular additive on the synthesis of LiNbO3 were investigated. PLL is a widely-studied biomolecule containing amino groups that can interact with solid inorganic clusters. The addition of PLL to a LiNbO3 precursor solution enhanced the aggregation of the produced LiNbO3 nanoparticles. This aggregation was induced by the electrical attraction of PLL with LiNbO3 nanoparticles, and was enhanced with increasing PLL molecular weight. Furthermore, the association of PLL with LiNbO3 nanoparticles was increased by the addition of methanol, which enhanced the miscibility of PLL with the precursor solution working as a co-solvent. The LiNbO3 nanoparticles generated with PLL exhibited piezoelectric properties without post-thermal treatment, suggesting that PLL contributes to the piezoelectricity. The results of this study are intriguing in terms of the potential for diverse engineering nanomaterials synthesis through a biomolecule that can also improve the physicochemical properties.

Electro-optical behaviour and dielectric dynamics of harvested ferroelectric LiNbO3 nanoparticle-doped ferroelectric liquid crystal nanocolloids

Nanocolloids comprising harvested ferroelectric LiNbO3 nanoparticles (≈25 nm) and ferroelectric liquid crystals were prepared and investigated. The impact of the amount of dispersed nanoparticles (0.01 wt%, 0.05 wt%, 0.10 wt%) on the electro-optical, dielectric and material parameters of the ferroelectric liquid crystals (FLCs) has been demonstrated. The dopant strongly influences the switching characteristics and has an effect on the saturation voltage of the FLC materials. Electro-optical measurements demonstrated that a relatively large (0.10 wt%) LiNbO3 dopant concentration decreases the response time and saturation voltage by approximately 40% and 25% respectively, compared with non-doped FLCs. The effect of LiNbO3 nanoparticle concentration on the material and dynamical parameters (i.e. spontaneous polarization, dielectric permittivity, dielectric absorption, dielectric strength, dc conductivity, and rotational viscosity) is presented. The observed behaviours are discussed in terms of capture of impurity ions on the surface of the harvested LiNbO3 nanoparticles. Ion capturing leads to enhancement of the localized electric field inside the smectic layers. The fast switching response and the low operational voltage of these FLC nanocolloids support their application in nanometric scale electronic devices.

Preparation of Lithium Niobate Nanoparticles by High Energy Ball Milling and their Characterization

We present investigations on the preparation of lithium niobate, LiNbO3 nanoparticles using high energy ball-milling. Stoichiometric composition of LiNbO3 powder was prepared by solid-state reaction method and used for ball-milling. Various milling parameter were optimized to get required particle sizes. Synthesized nanoparticles were characterized for their structure and particle sizes using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. The UV-Visible transmission shows the blue shift in cutoff, which indicate nearly stoichiometric composition of the prepared material. It has been observed that the sizes of particles decreases with increasing milling speed and time. Observed particle sizes were found in the range ~30-60 nm.

Study of Electronic Structure of LiNbO3 Nanoparticles by EELS

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Nanocomposite piezoelectric films of P(VDF‐TrFE)/LiNbO3

AbstractPiezoelectric films were prepared by incorporation of lithium niobate (LiNbO3) nanoparticles into copolymer of vinylidene difluoride and trifluoroethylene. Nanoparticles of LiNbO3 with ferroelectric phase were successfully synthesized and dispersed homogenously by ultrasonication in the copolymer matrix without any surfactant or surface functionalization. The nanocomposites were fully characterized by electronic microscopy, X‐ray diffraction, differential scanning calorimetry, dynamical mechanical analysis, and piezometer. Surprisingly, the copolymer matrix crystallinity and morphology were not affected by the incorporation of nanoparticles. Therefore the nanocomposites remained good mechanicals properties and high ferroelectricity coupled to nonlinear optical activity thanks to the noncentro symmetric space group of lithium niobate. This could be a novel approach to develop new multifunctional materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Kinetics and fabrication nanocrystallization of optical tellurophosphate glasses in system as: TeO2·P2O5·ZnO·LiNbO3

Tellurophosphate glasses with compositions (76−x)TeO2·9P2O5·15ZnO·xLiNbO3 (where x=12.5, 25, 30 and 35mol%) were prepared by the melting technique. Nanocrystallization and crystallization kinetics of the prepared glasses were investigated using DTA, XRD, HRTEM and SEM techniques. It is found that, the glass 51TeO2·9P2O5·15ZnO·25LiNbO3 has high extremely thermal stability (ΔT=189°C at heating rate 15Kmin−1). The mean value of the activation energy (〈Eg〉) for structural relaxation increases from 165 to 203±2kJ⋅mol−1. The activation energy for crystallization was found to be increased from 150.5 to 298.5±2kJ⋅mol−1 with the increase of LiNbO3 content. Values of Avarmi exponent were between 1.21 and 2.71 for the prepared glasses. Moreover, synthesized transparent glasses containing LiNbO3 nanoparticles have 16–46nm diameter were investigated by using XRD and HRTEM.

Multifunctional behaviour of mesoporous LiNbO3

Mesoporous LiNbO3 nanoparticles with BET surface area 185 m2 g−1 were synthesized by using Pluronic P123 as soft template. The samples showed three functionalities, viz., photoluminescence, ferroelectricity, and ferromagnetism. Room temperature photoluminescence was observed at 390 nm wavelength due to oxygen vacancy. The mesoporous LiNbO3 showed ferromagnetic behavior at room temperature. Ferroelectric behavior of the samples was confirmed from the P-E hysteresis loop measurement. The samples showed a magneto-dielectric effect with the dielectric constant increasing by ∼4.5% for an applied magnetic field of 10 kOe due to magnetostriction of the material which changed the lattice parameter to bring about an increase in the dipole moment of the unit cell.

Synthesis and piezoelectric response of cubic and spherical LiNbO3 nanocrystals

Methods have been developed for the shape-selective synthesis of ferroelectric LiNbO3 nanoparticles. Decomposition of the single-source precursor, LiNb(O-Et)6, in the absence of surfactants, can reproducibly lead to either cube- or sphere-like nanoparticles. X-Ray diffraction shows that the LiNbO3 nanoparticles are rhombohedral (R3c). Sample properties were examined by piezoresponse force microscopy (PFM) and Raman where both sets of nanoparticles exhibit ferroelectricity. The longitudinal piezoelectric coefficients, d33, varied with shape where the largest value was exhibited in the nanocubes (17 pm V−1 for the cubes versus 12 pm V−1 for spheres).

Synthesis of LiNbO(3) nanoparticles in a mesoporous matrix.

The synthesis of LiNbO3 nanoparticles in SBA-15 is reported for the first time. The preparation of nanoparticles was carried out by impregnation from the metal precursor and mesoporous silica SBA-15 as the template. A rapid one-step treatment in an IR furnace reduces the preparation time to only 10 min. In comparison, a conventional furnace requires 5 h reaction time to produce nanoparticles with similar textural properties. Another advantage of applying an IR furnace compared to conventional heating is the extremely high heating rate (up to 10 °C/s) and corresponding time saving. The resulting samples were investigated by powder X-ray diffraction, nitrogen physisorption, and high resolution transmission electron microscopy (HRTEM). The obtained nanoparticles are spherical with a diameter of approximately 10 nm.

Sol-gel derived ferroelectric nanoparticles investigated by piezoresponse force microscopy

Piezoresponse force microscopy (PFM) was used to investigate the ferroelectric properties of sol-gel derived LiNbO3 nanoparticles. To determine the degree of ferroelectricity we took large-area images and performed statistical image-analysis. The ferroelectric behavior of single nanoparticles was verified by poling experiments using the PFM tip. Finally we carried out simultaneous measurements of the in-plane and the out-of-plane piezoresponse of the nanoparticles, followed by measurements of the same area after rotation of the sample by 90° and 180°. Such measurements basically allow to determine the direction of polarization of every single particle.

New Synthesis of Nanosized Niobium Oxides and Lithium Niobate Particles and Their Characterization by XPS Analysis

This work presents a new synthesis of nano-sized lithium niobate particles by a low temperature three steps procedure. The complete protocol implies a LiH induced reduction of NbCl5 followed by in situ spontaneous oxidation into low valence niobium nano-oxides. These niobium oxides are exposed to air atmosphere leading to pure Nb2O5 formation. Finally, the stable Nb2O5 is converted into lithium niobate LiNbO3 nanoparticles during the controlled hydrolysis of the LiH excess. The nano-sized lithium niobate particles as well as their formation processes were characterized using X-ray photoelectron spectroscopy.

Effect of co-sensitization in new hybrid photo-refractive materials based on PVK polymer matrix and inorganic LiNbO3 nano-crystals

A new class of photo-refractive (PR) composite materials based on poly(N-vinylcarbazole) (PVK) (co-)sensitized with nano-crystalline lithium niobate (LiNbO3) is presented. The steady-state performance, as well as the kinetics of the photo-refractive grating formation, was investigated by degenerate four-wave mixing (DFWM) and two-beam-coupling (TBC) experiments. We found an optimum content of LiNbO3 nano-particles of only 10−3 wt.%. Even at concentrations as low as 10−7 wt.% a notable effect of the nano-crystals was detected. This yields materials with improved PR performance compared to that of the standard PR polymer material sensitized by TNF only. The role of LiNbO3 nano-particles is discussed in detail: The particles support generation and transport of the free-charge carriers. Furthermore, they increase the electron trap density.