7787-42-0Relevant articles and documents
Microstructure and microwave dielectric properties of Ba5Nb4O15-BaWO4 composite ceramics
Zhuang, Hao,Yue, Zhenxing,Zhao, Fei,Pei, Jing,Li, Longtu
, p. 411 - 415 (2009)
Microwave dielectric composite ceramics with compositions of (1 - x)Ba5Nb4O15-xBaWO4 (x = 0-1) were prepared by firing the mixture of Ba5Nb4O15 and BaWO4. The sinterin
Kinetics of formation of barium tungstate in equimolar powder mixture of BaCO3 and WO3: Thermogravimetric and spectroscopic studies
Al-Hajji, Latifa A.,Hasan, Muhammad A.,Zaki, Mohamed I.
, p. 43 - 49 (2010)
The formation of Barium monotungstate (BaWO4) particles in equimolar powder mixtures of BaCO3 and WO3 was examined under isothermal and non-isothermal conditions upon heating in air at 25-1200 °C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO2) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The x-t and x-T data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture quenched at various temperatures (600-1,000 °C) in the reaction course was analyzed by various spectroscopic and microscopic techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of WO3 species across the product layer (BaWO4), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118-125 kJ/mol) was found to be more credible than that (245 kJ/mol) determined non-isothermally.
Low-temperature properties of BaWO4 based on experimental heat capacity in the range 5.7–304u202fK
Musikhin,Bespyatov,Shlegel,Safonova
, p. 235 - 243 (2019)
The heat capacity of barium tungstate single crystal was measured by the adiabatic method in the range of 5.7–304 K. No anomalies in the heat capacity associated with the phase transition were found. The analysis of the functional behavior of heat capacity near zero revealed a low-frequency peak in the phonon density of states of BaWO4. An approach was proposed to allow quantitative description of the acoustic wing of the phonon density of states. The approximation of experimental data by an analytical expression was done, including the temperature region near 0 K. The Debye temperature at absolute zero has been obtained. The thermodynamic functions were calculated: entropy, enthalpy increment and Gibbs free energy.
Engineering Polar Oxynitrides: Hexagonal Perovskite BaWON2
Alemany, Pere,Canadell, Enric,Conejeros, Sergio,Cunquero, Marina,Fina, Ignasi,Fontcuberta, Josep,Frontera, Carlos,Fuertes, Amparo,Gàzquez, Jaume,Loza-Alvarez, Pablo,Oró-Solé, Judith,Ritter, Clemens
, p. 18395 - 18399 (2020)
Non-centrosymmetric polar compounds have important technological properties. Reported perovskite oxynitrides show centrosymmetric structures, and for some of them high permittivities have been observed and ascribed to local dipoles induced by partial order of nitride and oxide. Reported here is the first hexagonal perovskite oxynitride BaWON2, which shows a polar 6H polytype. Synchrotron X-ray and neutron powder diffraction, and annular bright-field in scanning transmission electron microscopy indicate that it crystalizes in the non-centrosymmetric space group P63mc, with a total order of nitride and oxide at two distinct coordination environments in cubic and hexagonal packed BaX3 layers. A synergetic second-order Jahn–Teller effect, supported by first principle calculations, anion order, and electrostatic repulsions between W6+ cations, induce large distortions at two inequivalent face-sharing octahedra that lead to long-range ordered dipoles and spontaneous polarization along the c axis. The new oxynitride is a semiconductor with a band gap of 1.1 eV and a large permittivity.
Low-temperature induced phase transitions in BaWO4:Er3+ microcrystals: A Raman scattering study
Carvalho,Sousa,Matos,Moura,Freire,Pinheiro,Luz-Lima
, (2020)
The synthesis of rare-earth-doped barium tungstate has increased in recent decades due to the attractive electrical and optical properties of the material. In this study, erbium-doped barium tungstate was synthesized by the co-precipitation method with three different concentrations: Ba(1-x)ErxWO4 (where x = 0.00, 0.01, and 0.02). The materials were characterized by X-ray diffraction (XRD), Raman and Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Subsequently, the samples were subjected to temperature variations in the range of 123–293 K, and their Raman spectra were collected to observe the structural changes induced by Er doping. We observed that at low temperatures, there was no indication of phase transition for pure tungstate (BaWO4); however, for doped tungstates, changes were observed in the Raman spectra, showing an unexpected structural phase transition.
Morphology-controlled synthesis of BaWO4 crystals via biominmetic SLM system
Dong, Feng-Qiang,Wu, Qing-Sheng,Ding, Ya-Ping
, p. 571 - 574 (2009)
BaWO4 crystals with various morphologies had been synthesized via a biominmetic system of supported liquid membrane in the presence of different additive reagents at room temperature. The X-ray diffraction patterns showed that the obtained BaWO
Dielectric and tunable characteristics of Ba0.4Sr 0.6TiO3-BaWO4 composite ceramics for microwave applications
Zhang, Mingwei,Zhai, Jiwei,Shen, Bo,Yao, Xi
, p. 1045 - 1050 (2011)
Phase compositions, microstructure and microwave dielectric properties, of BaWO4 (BW)-Ba0.4Sr0.6TiO3 (BST) composite ceramics, prepared by the traditional solid-state route, were systematically characterized. Meanwhile, mechanism of dielectric tunability of those materials was discussed. Dielectric properties of the BW-BST composites at a DC bias field near the phase transition temperature could be interpreted by using Johnson's phenomenological equation. The sample with x = 0.60 exhibited a tunability of 29.5%, a dielectric permittivity of 192 and a Q value of 231 (at 2.700 GHz), which make it a promising candidate for applications in electrically tunable microwave devices.
FORMATION OF A SERIES OF BARIUM TUNGSTEN BRONZES.
Ekstrom,Tilley
, p. 259 - 268 (1979)
The phases occurring in samples of gross composition Ba//xWO//3(0. 01 less than x less than 0. 33) heated at temperatures between 1073 and 1373 degree K have been determined using X-ray diffraction and electron microscopy. At all temperatures a tetragonal tungsten bronze phase with a narrow homogeneity range of x equals 0. 20-0. 21 was observed to form. In addition, at temperatures up to 1273 degree K, a series of orthorhombic intergrowth bronzes forms within a restricted composition range around x equals 0. 04. The latter phases are unstable at higher temperatures and were not found in preparations made at 1323 degree K. Similarly a new type of bronze phase forms at x equals 0. 14-0. 16 at temperatures up to 1323 degree K, but not at 1373 degree K. The structure of this phase is unknown. Aspects of the crystal chemistry of the barium bronzes and the relationships to other bronze phases are discussed.
Visible light photocatalytic degradation of crystal violet dye and electrochemical detection of ascorbic acid & glucose using BaWO4 nanorods
, p. 38 - 43 (2018)
Barium tungstate (BaWO?) rod like nanostructures were synthesized by slightly modified hydrothermal technique using sodium tungstate dihydrate (Na2WO?. 2H2O) as tungstate ion source and barium nitrate [Ba(NO?)?] as barium ion source.
Low-temperature sintering and microwave dielectric properties of Ba 5Nb4O15-BaWO4 composite ceramics for LTCC applications
Zhuang, Hao,Yue, Zhenxing,Zhao, Fei,Li, Longtu
, p. 3275 - 3279 (2008)
Low-temperature-sintered composite ceramics in Ba5Nb 4O15-BaWO4 system were prepared by cofiring mixtures of Ba5Nb4O15 and BaWO4 powders. Thermo-mechanical analysis indicated that a small amount of B 2O3 addition significantly promoted the densification process and lowered the sintering temperature to ～900°C. X-ray diffraction analysis revealed that Ba5Nb4O15 and BaWO4 coexisted in the sintered ceramics. With increasing B 2O3 content, a secondary phase, BaNb2O 6, appeared which affects the microwave dielectric properties. Microwave dielectric properties of the aforementioned compositions were as follows: dielectric constant of 16.8-19.2, Q × f values of 33 900-50 300 GHz, and a temperature coefficient of the resonant frequency of -3.4 to -8.6 ppm/°C. The chemical compatibility of BNW6502 ceramics with silver during the cofiring process has also been investigated, and no evidence of chemical reaction between Ag and ceramics was observed, indicating that the as-prepared composite ceramics are suitable for low-temperature cofired ceramics applications.
