High Temperature Gaseous Rare-Earth Permeation of Polyoxotungstates: An New Effective Method for the Preparation of Tungsten Bronzes

New polyoxometalate α-K 12H 3[Y(BW 11O 39) 2]·25H 2O was synthesized and treated by high temperature gaseous rare earth permeation to prepare tungsten bronze K 0.475WO 3. XRD, TG-DTA, XPS, 183W-NMR,CV and AC impedance spectra were used to characterize the resulting material. The results of XPS indicate that La has permeated and diffused into the body of the sample and exists in the forms of binding with other components. The crystal structure parameters of K 0.475WO 3 were obtained by the analysis of XRD, which shows tetragonal crystal system with lattice parameters: a=12 28 nm, c=3.833 nm, V=578.48 nm -3. The conductivities calculated from the results of AC impedance spectra of the material increase with the increasing of temperature, which shows a semiconductor character.

Dielectric Properties of Unfilled Tetragonal Tungsten Bronze Ba4PrFe(0.5)Nb(9.5)O(30) Ceramics

In order to found new dielectrics ceramics in tungsten bronze structure, unfilled tungsten bronze（TB） ceramics with nominal formula Ba4PrFe（0.5）Nb（9.5）O（30） were prepared by the solid state reaction method. The microstructure and dielectric properties were studied using powder X-ray diffraction, field emission scanning electron microscope, and variable temperature dielectric test system. The results show that the ceramics have a single phase and belong to the space group of P4bm with the cell of a = b = 12.4839（3） ？, c = 3.9409（5） ？, V = 614.192（2） ？3. The frequency dependent dielectrics properties show that the ceramics have a Debye-like relaxation at room temperature, while the temperature dependent dielectrics properties indicate that the ceramics are a relaxor and the relaxation is due to the nanopolars and oxygen vacancies. The ceramics have a potential application in electronic ceramics as temperature-stable multilayer ceramic capacitors.

Structural Analysis and Electrical Property of Tungsten BronzePrepared by Rare Earth Gaseous Permeation

The cubic sodium tungsten bronzes, Na_xWO_3(x=0.854 and 0.814)were prepared by rare earths gaseous permeation method. Structural analysis was carried out by Rietveld method from powder X-ray diffraction data. The X-ray diffraction profile calculated with cubic P32 models are in good agreement with the observed X-ray diffraction patterns. There is only a little difference in W-O bond and Na-O bond between Na_(0.854)WO_3 and Na_(0.814)WO_3. Conductivity measurements indicate that Na_xWO_3 show anomalous semiconducting behavior and percolation model was used to interpret it.

Characterization and Photocatalytic Activity of KSr_2Nb_5O_(15) with Tungsten Bronze Structure

Tungsten bronze （TB） type potassium strontium niobate KSr2Nb5O15 was prepared by solid-state reaction method, and was characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM） and UV-vis diffuse spectrum. The photocatalyst shows high photocatalytic activity of photodegrading acid red G. The effects of photocatalyst dosage and initial concentration of acid red G on the photodegradation process were studied. The kinetics of photocatalytic degradation of acid red G by KSr2Nb5O15 catalyst follows the first order reaction.

Preparation,Structure and Dielectric Properties of Tungsten Bronze Ferroelectrics in SrO-Eu_2O_3-TiO_2-Nb_2O_5 System

Compounds Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 with filled tetragonal tungsten bronze structure were prepared,and the dielectric characteristics and ferroelectric transition were investigated.Both ceramics displayed weak frequency dependence in room temperature dielectric constant,which decreased from 125 to 118 for Sr4Eu2Ti4Nb6O30,from 206 to 195 for Sr5EuTi3Nb7O30 in the frequency range of 10 kHz to 1 MHz.The present ceramics showed a diffuse ferroelectric phase transition.The frequency independent transition temperature （Tm） indicated the above compounds had no relaxor property.The diffuseness （γ） was 1.45 and 1.64 for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.The weak ferroelectric of the present materials are indicated from the P-E hysteresis loops,and a small 2Pr of 0.596 μC/cm2 and 0.068 μC/cm2 were observed for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.

Lithium-ion diffusion path of tetragonal tungsten bronze(TTB)phase Nb_(18)W_(16)O_(93)

By taking tetragonal tungsten bronze(TTB)phase Nb_(18)W_(16)O_(93)as an example,an improved solid-state sintering method at lower temperature of 1000℃for 36 h was proposed via applying nanoscale raw materials.XRD,SEM and XPS confirm that the expected sample was produced.GITT results show that the lithium-ion diffusion coefficient of Nb_(18)W_(16)O_(93)(10−12 cm^(2)/s)is higher than that of the conventional titanium-based anode,ensuring a relatively superior electrochemical performance.The lithium-ion diffusion mechanism was thoroughly revealed by using density functional theory simulation.There are three diffusion paths in TTB phase,among which the interlayer diffusion with the smallest diffusion barrier(0.46 eV)has more advantages than other typical anodes(such as graphite,0.56 eV).The relatively smaller lithium-ion diffusion barrier makes TTB phase Nb_(18)W_(16)O_(93)become a potential highspecific-power anode material.

Low Temperature Tetragonal Tungsten Bronze Oxides for Li-ion Storage

Nb-based tungsten bronze oxides have emerged as attractive materials in various fields,owing to the structural openings and simple synthesis method.In this work,the tetragonal tungsten bronze(TTB)NaWNbO_(6) was prepared by solid state reaction at a relatively low temperature of 775°C.The local structure was systematically studied by solid state nuclear magnetic resonance(SSNMR)with the aid of transition electronic microscopy(TEM).The analysis indicates that NaWNbO6 has pentagonal,square,and triangular tunnels.Notably,square tunnels were partly occupied(50%)by Na,which creates the ability for the Li-ion storage with a volumetric capacity of 210 A·h·L^(−1)at 0.2 C.The 2D ^(23)Na-^(23)Na EXSY results further suggest the ability of ions to fast exchange between the tetragonal and pentagonal tunnels,resulting in a high-rate performance 20 C.

A novel Sr_(5)BiTi_(3)Nb_(7)O_(30) tungsten bronze ceramic with high energy density and efficiency for dielectric capacitor applications

Dielectric capacitors with high capacitive energy storage are urgently needed to meet the growing demand for high-performance energy storage devices.Herein,a novel lead-free Sr_(5)BiTi_(3)Nb_(7)O_(30)(SBTN)tungsten bronze relaxor ferroelectric ceramic is pre­pared and explored for potential energy storage applications.A high recoverable energy density Wrec(~3.72 J/cm^(3))and ultrahigh efficiencyη(~94.2%)at 380 kV/cm are achieved simultaneously.Both Wrec andηexhibit superior stabilities against temperature(30-140°C),cycles(100-105)and frequency(1-500 Hz).In addition,a high current density of 796 A/cm^(2) and a large power den­sity of 71.7 MW/cm^(3) are achieved,together with good thermal endurance and fatigue resistance.These results demonstrate that the obtained SBTN ceramic can be deemed as the promising candidates for dielectric capacitor applications.

Electronic Transport Properties of Sodium Tungsten Bronzes Na_(0.54)WO_3 Single Crystals

Single crystals of ternary sodium tungsten bronzes have been prepared by the electrolysis of molten Na2W04-W03 system. X-ray powder diffraction and energy dispersive spectroscopy results reveal that the obtained samples are of cubic phase with empirical formula of Na0.54W03. Electrical resistivity measurement indicates a metallic conducting behavior without any anomaly from 5-300 K.

Sodium tungsten bronze(Na_(x)WO_(3))-doped near-infrared-shielding bulk glasses for energy-saving applications

Tungsten bronze coatings and films have attracted global attention for their applications in near-infrared(NIR)-shielding windows.However,they are unstable in strong ultraviolet,humid heat,alkaline and/or oxidizing environments and are difficult to be coated on glass surfaces with complex shape.Here,we address these limitations by doping sodium tungsten bronze(Na_(x)WO_(3))into bulk glasses using a simple glass melting method.X-ray diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy,TEM and SEM-EDS characterization confirmed the presence of sodium tungsten bronze(Na_(x)WO_(3))functional units inside the 34SiO_(2)-38B_(2)O_(3)-28NaF glass matrix.Because the functional units are well protected by the glass matrix,the fabricated glasses are stable under hot,humid,oxidizing conditions,as well as under ambient conditions,with no change after 360 days.The NIR-shielding performance of these glasses can be adjusted to as high as 100%by varying WO_(x)concentration(2-8 mol%)and quenching temperature(1000-1400℃).With a content of 6 mol%WO_(x)and a quenching temperature of 1000℃,the bulk glass shows 63%transmission of visible light and only 11%transmission of NIR light at 1100 nm.Thermal insulation experiments show that the NIR-shielding performance of the glasses are far superior to commercial soda lime window glass or indium-doped tin oxide(ITO)glass,and comparable to cesium tungsten bronze coated glass.The novel bulk glasses have higher stability,simpler processing,and can be easily made into complex shapes,making them excellent alternative materials for energy-saving glasses.

Potassium Tantalate K6Ta10.8O30 with Tungsten Bronze Structure and Its Photocatalytic Property

With the tunable and flexible physicochemical properties, tantalate photocatalysts with tungsten bronze struc- ture are worth being studied. In this work, we successfully synthesized a novel potassium tantalate K6Talo.8030 with tungsten bronze structure using a facile solid-state reaction route. The effects of calcination time on the phase com- position, morphology and crystallinity of the obtained samples were studied by XRD and SEM analyses. In addition, the photocatalytic activity of the samples was evaluated by the degradation of ARG dye under UV light irradiation. The results indicated that the K6Talo.8030 showed high photocatalytic activity for degradation of ARG and the pho- tocatalytic degradation of ARG followed the first order kinetics. Furthermore, the possible photocatalytic mecha- nism of the K6TamsO30 photocatalyst was proposed based on tungsten bronze structure feature and the scavengers experimental results. This study would give a new insight into tantalate photocatalysts.

Interdependence between electrical and magnetic properties of polycrystalline cobalt-substituted tungsten bronze multiferroic ceramics

Polycrystalline cobalt-substituted tungsten bronze ferroelectric ceramics with chemical composition Ba_(5)CaTi_(2-x)Co_(X)Nb_(8)O_(30)(x=0.00,0.02,0.04 and 0.08)were synthesized by solid state reaction technique.X-ray diffraction(XRD)technique was used to confirm the phase formation and it revealed the formation of single phase tetragonal structure with space group P4bm.The surface morphology of the samples was studied by using the scanning electron microscopy(SEM)technique.The dielectric properties such as dielectric constant and dielectric loss have been investigated as a function of temperature and frequency.The P-E and M-H studies confirmed the coexistent of ferroelectricity and magnetism at room temperature.The P-E loop study indicated an increase in the coercive field while the M-H study depicted a decrease in the magnetization with the incorporation of cobalt ions.

Synthesis and X-ray Powder Diffraction Characterization of A New Niobate Crystal Ba_4Na_2VNb_9O(30)

A new niobate crystal Ba4Na2 VNb9O30 was synthesized in BaO-Na2O-V2O5-Nb2O5 system for the first time. Its shape, optical properties , melting point and chemical stability were studied. X - ray powder diffraction study determined that this compound assumes a tetragonal tungsten bronze structure with space group P4bm(100) and lattice parameters a = b= 12.4275(2),e=3.970(3). The new compound may be one kind of photorefractive crystals.

SYNTHESIS AND CRYSTAL STRUCTURE OF A NEW COMPOUND Sr_6Sn_2Nb_8O_30

A new compound Sr6Sn2Nb8O30 was found in the ternary system of SrO-SnO2-Nb2O5. The transparent colorless crystal with needle-like shape can be grown by flux method. The crystal structure of new compound was determined by X-ray diffraction, and its belongs to tungsten bronze structure. Sr6Sn2Nb8O30 crystallizes in orthorhombic system with unit cell parameters a= 17. 579 (DA,6= 17. 509(DA,c=7. 7880(5)A,Z = 4 and space group Cmm2.

Initial Study of Strontium Barium Niobate/Strontium Barium Titanium Ceramics through A Modified Sol-Gel

Barium strontium titanate niobate (BSTN) composite ceramics system following the general formula 0.5BaO·0.5SrO·0.5TiO2·0.5Nb2O6 was successfully prepared. The investigation is carried out through a modified sol-gel method. By controlling the viscosity of the sol solution to suspend the strontium barium niobate ceramic powder uniformly which had been made beforehand and the viscosity of the sol could be changed by adjusting the mixture ratio of the precursor. Powders obtained from dried gels were calcined at 800 ℃ for 3 h. The bulk ceramics obtained from the dried powders were sintered at the temperatures of 1250 and 1300 ℃ respectively. The results of the XRD and SEM indicated that the perovskite phase and the tungsten bronze phase could be coexisted stably in BSTN at both of these temperatures. The increasing of the sintering temperature was good for the crystal phase growing and the solubility of the two phases in the composite ceramics. And the theory of adulteration could be adopted to resolve the phenomena that sintering temperatures too high, which resulted in the crystalline grains growing singularly. Some problems were put forward to pay attention to this material research process.

Preparation, Characterization and Dielectric Properties of Ba_6Mg_(0.67)Nb_(9.33)O_(30) Ceramic

A new niobate Ba6Mg0.67Nb9.33O30 was ssnthesized in the BaO-MgO-Nb2O5 system by solid state reaction at 1350 ℃ for 48 b. The strncture and dielectric properties of Ba6Mg0.67Nb9.33O30 were determined by X-ray pouder diffraction, straining electron microscopy and dielectric measurements. The results show that Ba6Mg0.67Nb9.33O30 belongs to ferroelectric phase of filled tetragonal tungsten bronze structure at room temperature with unit cell parameters ： a = 1. 26052（4） nm , c = 0.40045（2） nm, space group P4bm , calculated density 5 . 707g. cm ^-3 . Ba6Mg0.67Nb9.33O30 belongs to relaxor ,ferroetectrics undergoing diffusive phase transition, and the transition temperature （ Tc ） is 30 ℃ observed at 10 kHz. At room temperature, Ba6Mg0.67Nb9.33O30 eeramic has a high dielectric constant 850 at 1 MHz and a low dielectric loss of 0. 0052.

Synthesis and Characteristic of a New Niobate:Ba_5NaCo_(0.5)Nb_(9.5)O_(30)

A new niobate crystal was synthesized for the first time in BaO-Na2O-Co2O3 -Nb2O5 system by solid state reaction and the flux method. The new compound was studied by X-ray diffraction, electron probe. N-ray microanalysis, chemical analysis and SEM. The result of the X-ray diffraction shows that Ba5 NaCo0.5 Nb9.5 OK) belongs to tetragonal tungsten bronze structure with space group P4bm( 100) and lattice parameters a = b = 12.4453(2) A, c = 3. 9770 (3) A and Z = 1. The structure of the compound is different from that ofBa4Na2Nb10O30

Preparation, Characterization and Dielectric Property of Sr_5LaTi_3Nb_7O_(30) Ceramic

Sr-5LaTi-3Nb-7O- 30 ceramic was prepared by the conventional high temperature solid-state reaction route. The sintered samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), differential thermal calorimetry (DSC) and dielectric measurements.The results show Sr-5LaTi-3Nb-7O- 30 belongs to paraelectric phase of filled tetragonal TB structure at room temperature, and undergoes a diffuse phase transition in the temperature range of -54-34 ℃.And Sr-5LaTi-3Nb-7O- 30 ceramic shows a high dielectric constant of 479 with a low dielectric loss of 0.005 at 1MHz. In comparison with Ba-based ceramics with TB structure, the temperature coefficients of the dielectric constant (τ-ε) is significantly reduced.

High Dielectric Constant and Low-loss Dielectric Ceramics of Sr_5 LnTi_3Ta_7O_(30)(Ln=La,Nd,Sm and Y)

Polycrystalline Sr5LnTi3Ta7O30 （Ln=La, Nd, Sm and Y） ceramics were prepared as single-phase materials through conventional solid-state ceramics method. The structure was characterized by X-ray diffraction method and scanning electron microscopy （SEM）. The dielectric properties were measured from room temperature to 400℃. All compounds are paraelectric phases adopting the filled tetragonal tungsten bronze （TB） structure at room temperature. At 1 MHz their dielectric constant （ετ） varied from 109 to 139, dielectric loss changed from 0.003 3 to 0.005 8, and the temperature coefficients of the dielectric constant （τε） moved from -710 to -880×10^-6℃^-1.

Characterization of Modified Sol-Gel Derived xSrO·(1-x)BaO·0.5Nb_2O_5·0.5TiO_2 Composite Ceramics

Strontium barium niobate/barium strontium titanate composite ceramics of xSrO·(1-x)BaO·0.5Nb2O5·0.5TiO2 (BSTN in short) with a range of Sr/Ba ratios were fabricated using a modified sol-gel method with Nb2O5 fine powders suspended in the barium strontium titanate (BST in short) sol solution. Powders obtained from dried gels were calcined at 800 ℃ for 3 h. After preparing bulk ceramics from these powders by sintering at 1200 ℃ for 3 h, the tetragonal tungsten bronze(TTB) phase and perivoskite phase were co-present in compositions between 0.25≤x≤0.75, with the increasing of x value, the peaks of pervoskite phase shift to the high angle position slightly while no changes happened in the peak position of TTB phase. The peak intensity of both two phases were also changed.