Barium Sodium Niobate Research Articles

Structural and photoluminescent features of Eu3+ activated single‐phase niobate phosphor for lighting applications

AbstractSingle‐phase barium sodium niobate phosphor (Ba2NaNb5O15: BNNO) doped with europium (Eu3+) ions have been synthesized by solid‐state reaction route. Pure and single‐phase formation with the tetragonal structure of the synthesized Eu3+‐doped BNNO (BNNO: Eu3+) phosphor was confirmed by X‐ray diffraction. The SEM image of BNNO sample indicates irregular morphology and nonuniform micron‐sized particle formation. The intense excitation peak located at 463 nm appeared in the excitation spectrum for BNNO: Eu3+ phosphors when monitored atred (615 nm) emission of Eu3+ ions. Under 463 nm excitation, the emission spectra for BNNO: Eu3+ exhibit dominant red (615 nm) emission peak. The luminescence intensity increases progressively up to the 10.0 mol% of Eu3+ ions and decreases further due to the concertation quenching effect. The energy transfer mechanism responsible for concentration quenching has been investigated in detail. The chromaticity coordinates assessed for BNNO: Eu3+ phosphors, which are located in the red region of Commission International de l'Eclairage 1931 diagram. The structural, morphological, and spectroscopic results attained for the synthesized phosphor (BNNO: Eu3+) demonstrate potential candidature as a red component phosphor in solid‐state lighting applications.

Ferroelectricity in biological building blocks: Slipping on a banana peel?

Ferroelectricity in biological system has been anticipated both theoretically and experimentally over the past few decades. Claims of ferroelectricity in biological systems have given rise to confusion and methodological controversy. Over the years, a “loop” of induced polarization in response to a varying applied electrical field and a consequent polarization reversal has prompted many researchers to claim ferroelectricity in biological structures and their building blocks. Other observers were skeptical about the methodology adopted in generating the data and questioned the validity of the claimed ferroelectricity as such, “loop” can also be obtained from linear capacitors. In a paper with somewhat tongue-in-cheek title, Jim Scott showed that ordinary banana peels could exhibit closed loops of electrical charge which closely resemble and thus could be misinterpreted as ferroelectric hysteresis loops in barium sodium niobate, BNN paraphrasing it as “banana”. In this paper, we critically review ferroelectricity in biological system and argue that knowing the molecular and crystalline structure of biological building blocks and experimenting on such building blocks may be the way forward in revealing the “true” nature of ferroelectricity in biological systems.

Broadband Brillouin scattering study of ferroelectric instability of barium sodium niobate

The barium sodium niobate (BNN) with tungsten-bronze structure is one of well-known optical crystals for electro-optic and nonlinear optic applications. This paper reviews the ferroelectric instability of BNN crystals. BNN is a uniaxial ferroelectric with a spontaneous polarization along the tetragonal c-axis. There is no report on the observation of an optical soft mode responsible for a ferroelectric phase transition. In the vicinity of the Curie temperature, TC = 560°C, an intense central peak (CP) related to the polarization fluctuations along the c-axis was observed by the broadband Brillouin scattering experiment. The relaxation time determined by the CP width shows the critical slowing down towards TC. This fact indicates that the ferroelectric instability of BNN is an order-disorder type.

Structures and phase transitions in barium sodium niobate tungsten bronze (BNN)

The room-temperature structure of the filled tetragonal tungsten bronze, Ba2NaNb5O15 (BNN), has been the subject of a number of studies, and these studies have given an almost corresponding number of different results. From a group theoretical examination of the different possibilities and a review of the published experimental results we conclude that the room-temperature structure is that proposed by Labbé et al. [J. Phys. Condens. Matter (1989), 2, 25–43] in the space group Bbm2 (Ama2 in standard setting) on a 2\sqrt{2}a × \sqrt{2}a × 2c cell. Upon heating, the structure remains ferroelectric but becomes tetragonal (space group P4bm) at 550 K, then paraelectric (space group P4/mbm) at and above 860 K.

Synthesis and optimization of photoluminescence properties in potential reddish orange emitting niobate phosphor for photonic device applications.

A series of samarium ions (Sm3+ ) activated barium sodium niobate (Ba2 NaNb5 O15 ) samples have been successfully synthesized via employing a solid-state reaction technique. Single phase, crystalline tetragonal Ba2 NaNb5 O15 were formed and the crystallite size of the prepared sample varied with doping of Sm3+ ions. The scanning electron microscopy (SEM) images of Ba2 NaNb5 O15 :Sm3+ illustrate that the particles possess a non-uniform spherical structure with some agglomeration. The prepared Ba2 NaNb5 O15 :Sm3+ phosphors were efficiently excited with near-ultraviolet (n-UV) (406 nm) and emit strong visible emission peaks in the range 550-725 nm. The phenomenon of concentration quenching was detected after x = 0.10 mol of Sm3+ ions concentration for Ba2 NaNb5 O15 , which arises due to non-radiative energy transfer through dipole-dipole interaction among activator ions. Colour coordinates (0.586, 0.412) for the optimized phosphor lies in the visible reddish orange region. A bi-exponential decay behaviour was observed for the photoluminescence decay curve of the optimized phosphor sample with an average decay time in milliseconds. The temperature dependent emission intensity confirms that the Ba2-x NaNb5 O15 :xSm3+ (x = 0.10 mol) phosphor exhibits adequate thermal stability having high value of activation energy (ΔE = 0.201 eV). The comprehensive study and analysis of the as-prepared samples suggest that the intense reddish orange emitting thermally stable Ba2 NaNb5 O15 :Sm3+ phosphor can act as a potential luminescent material in phosphor coated lighting, solar cells and other photonic devices.

Effect of the BaO-Na2O-Nb2O5-P2O5 glass addition on microstructure and dielectric properties of BNN ceramics

Barium sodium niobate Ba2NaNb5O15 (BNN) ceramics with different amounts of BaO-Na2O-Nb2O5-P2O5 (BNNP) glass were prepared via the conventional solid-state method. The effect of glass content on structural, microstructure and dielectric properties of BNN ceramics was investigated. The XRD results showed that no secondary phase was formed after adding BNNP glass. It was found that such additions reduce the average grains size and refine the microstructure of the obtained ceramics. Moreover, the samples exhibited a stable dielectric constant over the temperature range of 25°C–150°C and their dielectric constants were significantly improved. The ceramic with 7.5 wt% BNNP glass content showed a dielectric constant which is more than twice as much as that of pure BNN ceramic, as well as a low dielectric loss less than 5%.

A comparative study on piezoelectric and piezoresistive pressure sensor using COMSOL simulation

For system stability monitoring, pressure is one of the major and easy quantity to be measured among the many other physical quantities. A pressure sensor produces a signal as a function of the pressure imposed. These sensors became a vital part of our everyday life from devices we use at home to industrial equipment. In this paper, simulation, and comparative study of piezoresistive and piezoelectric pressure sensor is presented. All the simulations where made using COMSOL Multiphysics software of 5.5 version. Using this software, 3D models of sensors are simulated with different materials. From this simulation results, best materials for piezoelectric and piezoresistive pressure sensor are selected. This work follows the simulation, and analysis of a piezoresistive pressure sensor, done using four different sets of piezoresistive materials. Both p-type and n-type single crystalline silicon and polycrystalline silicon materials are used for the piezoresistive pressure sensor simulation. Pressure vs. displacement graphs of four set of piezoresistive materials are plotted. Displacement which is obtained in micrometer range increases with different input load from 100 KPa to 500 KPa. A piezoceramic tube, example for piezoelectric pressure sensor simulation also carried out using different piezoelectric materials like PZT 5A, PZT 5H, PVDF, BaTiO3, Lithium Tantalate, Cadmium Sulfide, Lithium Niobate, Aluminum Nitride and Barium Sodium Niobate. The modelling and simulation of Piezoceramic tube- Piezoelectric pressure sensor is done by giving different input pressure values. During the simulation of direct piezoelectric effect, voltage generation is obtained according to the input pressure. Output voltages of different piezoelectric materials are taken by giving different boundary load from 0.1 MPa to 1 MPa. Indirect piezoelectric effect simulation is also done, where piezoelectric materials become strained when the electric field is applied and this strain is directly proportional to the electric field. A Displacement table of indirect piezoelectric effect is measured by giving constant input pressure of 0.1 MPa. Here, analyses are done in MPa range of input pressures, obtained voltage in V and displacement in micrometers. Pressure vs. Voltage values for direct piezoelectric effect is plotted Efficiency and resolution of piezoresistive and piezoelectric pressure sensors are found out.

Structural and electrical properties of Nd3+ doped ferroelectric barium sodium niobate ceramics

Ferroelectric polycrystalline samples of Ba4Na2Nb10O30 with rare earth neodymium ion, member of the family of TB, were prepared using a high temperature solid state reaction technique and studied their electrical properties in a range of temperature (RT-to 300 °C) at 1KHz. X-ray diffraction analysis of these compounds shows the formation of single phase tetragonal structure at room temperature. Detailed studies of the dielectric properties suggest that they have undergone diffuse ferroelectric–paraelectric phase transition well above the room temperature. It has also been found that as the concentration of the neodymium increases, Curie temperature observed to be decreased. Measurements of electrical DC Conductivity as a function of temperature suggest that the compounds have semi conductivity properties the temperature, with positive temperature coefficient of resistance (PTCR) behavior.

Raman and Hyper Raman opalescence on the soft mode in barium sodium niobate crystals

Abstract A strong increase in the spectral intensity of Raman scattering (Raman opalescence effect) at the polar soft mode, responsible for the instability of the crystalline lattice, near ferroelectric phase transition points in the barium sodium niobate (BSN) crystal was found. Raman opalescence is explained as a consequence of a sharp increase in the amplitude of the transverse A1(Z; TO) polar optical soft mode near the temperature of the ferroelectric phase transition in BSN (Tc = 830 K). Experimental results were obtained using a new experimental technique, based on the construction of isofrequency temperature dependences, when registering the spectral intensity of Raman scattering at fixed frequencies of the spectrometer, near the frequency of the exciting line, for certain polarization geometry. The conditions for observing the effects of Hyper Raman opalescence near the phase transition temperature in the BSN are established.

Enhanced energy-storage density in sodium-barium-niobate based glass-ceramics realized by doping CaF2 nucleating agent

The barium sodium niobate (BNN) glass-ceramics with different amount of CaF2 addition were fabricated by melting-crystallization method. Effects of CaF2 on microstructure, phase compositions, interface polarization, dielectric, energy-storage and charge–discharge properties of the BNN-glass-ceramics were comprehensively studied. Results indicate a suitable amount of CaF2 (from 1.0 to 3.0 mol%) is helpful to improve both relative permittivity and breakdown strength (BDS) of the BNN-glass-ceramics. The theoretical energy-storage density is up to 14.3 J/cm3 when the amount of CaF2 reaches 3.0 mol%. The optimal composition of 3.0 mol% CaF2 addition was further evaluated by a pulsed charged–discharged circuit and P–E hysteresis loops, from which we can conclude BNN-glass-ceramic is an excellent linear dielectric material. And the stored energy could be released within 50 ns and discharge power density reaches 75.6 MW/cm3. It’s for such results that the glass-ceremics with CaF2 addition are promising materials for pulse power applications.

Nanodomain structures in nonlinear crystal

Thermal properties of barium sodium niobate crystals were investigated by means of light scattering methods in the temperature range of 20–600°С. Three types of pictures, ellipses, rounds, stripes, have been observed on the screen in the far field depending on the temperature and polarization of the laser beam relatively to the crystallographic axes. The changes of the type of scattering are correlated with structural phase transitions at about 300 °C and 560 °C and with the evolution of the nano-domain structures at about 200 °C and 250 °C. Image analysis in the temperature region of 20–600 °C and comparison with the structural investigations below 300 °C allow to made conclusion that incommensurate phase in the temperature range of about 500–550 °C has the quasi-tetragonal symmetry.

Effects of crystallization temperature on phase evolution and energy storage properties of BaO-Na2O-Nb2O5-SiO2-Al2O3 glass-ceramics

Barium sodium niobate (BNN) glass ceramics were successfully fabricated with controllable crystallization by technology for heating processing and the effects of crystallization temperatures on phase evolution, microstructure, dielectric properties and breakdown strength were investigated systematically. In addition, the empirical power-law dependence of breakdown strength on thickness (Eb∝d-n) was confirmed in BNN glass-ceramic system with an exponent n of 0.21. Based on the results, the BNN glass ceramic crystallized at 800 °C presents a remarkable breakdown strength (BDS) of 2322 kV/cm with the tested thickness of 30 μm, and the highest energy density of 16.6 J/cm3 was achieved.

Effect of Microwave Processing on the Crystallization and Energy Density of BaO‐Na2O‐Nb2O5‐SiO2‐B2O3 Glass‐Ceramics

Barium sodium niobate (BNN) glass‐ceramics were successfully synthesized through a controlled crystallization method, using both a conventional and a microwave hybrid heating process. The dielectric properties of glass‐ceramics devitrified at different temperatures and conditions were measured. It was found that the dielectric constant increased with higher crystallization temperature, from 750°C to 1000°C, and that growth of the crystalline phase above 900°C was essential to enhancing the relative permittivity and overall energy storage properties of the material. The highest energy storage was found for materials crystallized conventionally at 1000°C with a discharge energy density of 0.13 J/cm3 at a maximum field of 100 kV/cm. Rapid microwave heating was found to not give significant enhancement in dielectric properties, and coarsening of the ferroelectric crystals was found to be critical for higher energy storage.

Investigations into the structural and down-shifting and up-conversion luminescence properties of Ba2Na1−3xErxNb5O15 (0 ≤ x ≤ 0.06) nanocrystalline phosphor synthesized via sol-gel route

The present work deals with the structural and efficient down-shifting (DS) and up-conversion (UC) luminescence properties of erbium ion (Er3+) doped nanocrystalline barium sodium niobate (Ba2Na1−3xErxNb5O15, where x = 0, 0.02, 0.04 and 0.06) powders synthesized via novel citrate-based sol-gel route. The monophasic nature of the title compound was confirmed via x-ray powder diffraction followed by FT-IR studies. High-resolution transmission electron microscopy (HRTEM) facilitated the establishment of the nanocrystalline phase and the morphology of the crystallites. The Kubelka–Munk function, based on diffused reflectance studies and carried out on nano-sized crystallites, was employed to obtain the optical band-gap. The synthesized nanophosphor showed efficient DS/PL-photoluminescence and UC luminescence properties, which have not yet been reported so far in this material. The material emits intense DS green emission on excitation with 378 nm radiation. Interestingly, the material gives intense UC emission in the visible region dominated by green emission and relatively weak red emission on 976 nm excitation (NIR laser excitation). Such a dual-mode emitting nanophosphor could be very useful in display devices and for many other applications.

Elastic anomaly and aging of new type of incommensurate phase transition in ferroelectric barium sodium niobate

The lattice instability of the incommensurate (IC) phase transition of uniaxial ferroelectric Ba2NaNb5O15 (BNN) was investigated by micro-Brillouin scattering. Spectra of the longitudinal acoustic (LA) mode were observed from room temperature to 750 K. In the vicinity of the IC phase transition temperature TIC = 573 K, elastic anomalies in the form of a sharp peak in the sound velocity and thermal hysteresis during the heating and cooling cycle were observed. During this transition, the crystal point group changed from tetragonal 4mm to orthorhombic 2mm along with the IC modulation. In order to deepen our understanding of the thermal hysteresis, aging experiment in the IC phase was conducted. We can conclude that the appearance of thermal hysteresis related to the relaxation of ferroelastic strain is related to the feature of the new type III IC phase transition mechanism of BNN.

Frequency and Temperature‐Independent Electrical Transport Properties of 2BaO–0.5Na2O–2.5Nb2O5–4.5B2O3 Glass‐Ceramics

The temperature (300–973 K) and frequency (100 Hz–10 MHz) response of the dielectric and impedance characteristics of 2BaO‐0.5Na2O–2.5Nb2O5–4.5B2O3 glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100 Hz–10 MHz) and temperature (300–600 K). The temperature coefficient of dielectric constant was 8 ± 3 ppm/K in the 300–600 K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal‐glass interface, leading to a high value of effective dielectric constant especially for the samples heat‐treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (Pr) increased with the increase in crystallite size.

Elastic anomaly and order-disorder nature of multiferroic barium sodium niobate studied by broadband brillouin scattering

The successive phase transitions of multiferroic barium sodium niobate, Ba2NaNb5O15 (BNN), were studied by Brillouin scattering. The LA, TA modes, and central peak were measured in a large temperature range from room temperature up to 750 °C. In the vicinity of a ferroelectric phase transition at about TC = 585 °C from the prototypic tetragonal 4/mmm to ferroelectric 4mm phases, elastic anomaly was observed for LA and TA modes. In addition, the order-disorder nature was observed by the temperature dependence of a central peak. For further cooling another elastic anomaly was also observed in the vicinity of a ferroelastic incommensurate phase transition at about TIC = 285 °C into orthorhombic 2mm phase with the appearance of incommensurate modulation. The large thermal hysteresis of elastic anomaly near TIC can be attributed the typical feature of the type III incommensurate phase transition predicted recently by Ishibashi and Iwata (2013 J. Phys. Soc. Jpn. 82 044703).

2P1-1 Elastic anomaly and aging of new type of incommensurate phase transition in ferroelectric barium sodium niobate(Poster Session)

2P1-1 Elastic anomaly and aging of new type of incommensurate phase transition in ferroelectric barium sodium niobate(Poster Session)

Synthesis, structural and optical properties of nanocrystalline Ba2NaNb5O15

Fine powders comprising nanocrystallites of barium sodium niobate, Ba2NaNb5O15 (BNN) were obtained via a citrate assisted sol–gel route at a much lower temperature than that of the conventional solid-state reaction route. The phase evolution of BNN as a function of temperature was investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). DTA data followed by XRD studies confirmed the BNN formation temperature to be around 923 K. The as-synthesized powders heat-treated at 923 K/10 h attained an orthorhombic structure akin to that of the parent BNN phase. Transmission electron microscopy revealed that the nanocrystallites are associated with dislocations. The optical band gap was calculated using the Kubelka–Munk function. These nanocrystallites exhibited strong visible photoluminescence (PL) at room temperature. The PL mechanism was explained by invoking the dielectric confinement effect, defect states and generation of self-trapped excitons.

Viscoelastic and thermal analysis of barium sodium niobate polystyrene nanocomposites: role of constrained polymer layer

Nanocrystalline powders of barium nodium niobate have been prepared by conventional ceramic technique. The powders belonged to a tungsten bronze type structure with tetragonal symmetry and lattice constants ‘a’ = 1·24214 nm and ‘c’ = 0·39028 nm. Composites were prepared by mixing powders of barium sodium niobate Ba3Na4Nb10O30 (BNN) with polystyrene (PS) at different volume fractions of the material. The viscoelastic, tensile and dielectric properties of BNN-PS nanocomposites were investigated with special reference to the effect of filler loading, frequency and temperature. The composites showed a significant increase in storage modulus in the glassy and rubbery regions. The tan δ peak temperature of the composites is shifted to the higher temperature region, and the peak intensity is lowered for all combinations. The composites showed a shift in cross-over frequency to the lower side, suggesting a delayed relaxation of the molecular chains in the presence of BNN, and this shift is found to depend on the content of BNN. The modulus enhancement is related to the volume of the added BNN as well as the volume of the constrained polymer. The study of the constrained volume of the polymer indicates that the structure of the ceramic nanocomposite possesses a strong interfacial interaction. The compatibility of the composites is observed through the Cole–Cole plots. The core shell morphology is predicted for the composite cross-section.