BaTi4O9 Research Articles

Barium titanate photocatalysts with silver-manganese dual cocatalyst for carbon dioxide reduction with water.

Titanate photocatalysts with suitable cocatalysts are promising candidates for photocatalytic CO2 reduction, with the use of water as an electron donor. Here, several barium titanates with various compositions were examined, and BaTi4O9 (BT4) was found to be the best photocatalyst with the assistance of an Ag cocatalyst for photocatalytic CO2 reduction to form CO. The photocatalytic activity was further enhanced by the use of MnOx as an additional cocatalyst to construct an Ag-MnOx/BT4 photocatalyst, where Ag and MnOx were selectively deposited at different facets on BT4 crystal and functioned as active sites for CO2 reduction and water oxidation, respectively. As for the oxidative products from water, molecular oxygen (O2) and hydrogen peroxide (H2O2) were obtained.

Boosting BaTi4O9 photocatalytic H2 evolution activity by functionalized CuNi alloy

H2 evolution through photocatalysis possesses has the advantage for achieving the carbon neutral, that relies on the highly efficient catalysts. Non-noble metals have lower prices than noble metals, which is beneficial for their large-scale applications in industry. In this paper, functionalized CuNi alloy and BaTi4O9 (BTO) composite (CuxNiy/BTO(Z)) photocatalyst were synthesized successfully through hydrothermal calcination method. The acetates were selected the raw material to avoid the use of hazardous chemicals and pollution of photocatalysts by other elements, while also providing C=O for the photocatalyst to further enhance its photocatalytic activity. Under visible light irradiation, the photocatalytic hydrogen (H2) evolution rate of Cu3Ni/BTO is 184.14 μmol·g−1·h−1, which is 101.18 times that of pure BTO (1.82 μmol·g−1·h−1) under the same conditions. Combining density functional theory (DFT) calculations and experimental studies, it is concluded that electronic structural characteristics of BaTi4O9 and the addition of CuNi alloy could provide more electrons and improve the photocatalytic H2 evolution activity.

Study on low temperature sintering behavior and dielectric properties of BaTi4O9/La2O3-B2O3-CaO microwave dielectric ceramic

In this paper, La2O3-B2O3-CaO (LBC) glass ceramics were sintered at low temperature to density BaTi4O9 (BT4) microwave dielectric ceramics. The effects of composition ratio and sintering temperature on the micromorphology, phase composition and microwave dielectric properties of LBC/BT4 multiphase ceramics were investigated. Experimental results showed that LBC microcrystalline glass and BT4 happened between the ceramic interface reaction obviously, and with the increase of microcrystalline glass content and sintering temperature increases, density, dielectric constant epsilon εr value and the quality factor Qf value were increased after the first decrease. And the resonant frequency temperature coefficient of τf value with the increase of LBC content decreases, and with the increase of sintering temperature, it goes up and then it goes down. When the content of LBC glass ceramics is 50 wt%, LBC/BT4 multiphase ceramics sintered at 875 °C for 2 h have good microwave dielectric properties εr = 26, Qf = 8000 GHz, τf; = +150 ppm/°C.

Structural, optical and microwave dielectric properties of Ba(Ti1\u2212xSnx)4O9, 0\u2009\u2264\u2009x\u2009\u2264\u20090.7 ceramics

Sn-doped BaTi4O9 (BT4) dielectric ceramics were prepared by a mixed oxide route. Preliminary X-ray diffraction (XRD) structural study shows that the ceramic samples have orthorhombic symmetry with space group (Pnmm). Scanning electron microscopy (SEM) shows that the grain size of the samples decreases with an increase in Sn4+ content. The presence of the metal oxide efficient group was revealed by Fourier transform infrared (FTIR) spectroscopy. The photoluminescence spectra of the ceramic samples reported red color ~ 603, 604, 606.5 and 605 nm with excitation energy ~ 2.06, 2.05, 2.04 and 2.05 eV for Sn4+ content with x = 0.0, 0.3, 0.5, and 0.7, respectively. The microwave dielectric properties of these ceramic samples were investigated by an impedance analyzer. The excellent microwave dielectric properties i.e. high dielectric constant (εr = 57.29), high-quality factor (Qf = 11,852), or low-dielectric loss (3.007) has been observed.

Investigation of the composites of epoxy and micro-scale BaTi4O9 ceramic powder as the substrate of microwave communication circuit

BaTi4O9 (BT4) ceramic was sintered at 1270 °C and ground into fine ceramic powder with average particle size of about 3 μm. After that, the micro-scale BT4 ceramic powder with different concentrations (from 5 to 70 wt%) was mixed with O-Cresol Novolac (OCN) epoxy resin to form flexible epoxy-BT4 composites. The dielectric constant of epoxy-BT4 composites was first measured from 100 kHz to 100 MHz at room temperature by using the “plate method”. The measured dielectric constants of epoxy-BT4 composites were compared with the values predicted by Lichtenecker equation. We would show that the measured results were well fitted with the predicted values. In order to investigate the composites of epoxy and micro-scale BT4 ceramic powder for the application of microwave communication, the dielectric constants of epoxy-BT4 composites were also measured from 1 to 10 GHz at room temperature by using a “square cavity resonator” method. As the measured frequencies were at the range of GHz, the dielectric constants of epoxy-BT4 composites were almost unchanged with the increase of frequency. It conjectured that epoxy-BT4 composites could be used as the flexible substrates to fabricate the microwave filters and antennas.

Control of coring effect in BaTi4O9 microwave dielectric ceramics by doping with Mn4+

In the present work, we have attempted to reduce the effect of coring effect in the titanate ceramic system BaTi4O9 (BT4) by doping it with Mn4+. The microwave dielectric BaTi4O9 ceramics doped with 0, 0.5 and 1.0mol% Mn4+ were synthesized by conventional ceramic processing route. The XRD studies confirmed a single phase crystalline structure for all the ceramic samples studied. The SEM micrographs of the ceramics reveal a microstructural change leading towards a more uniform grain size distribution as the Mn4+ content increases to 1.0mol%. In the low frequency region (100Hz to 1MHz), the temperature stability of dielectric properties exhibits a marked improvement with the increasing amount of Mn4+ in the ceramic system. In the microwave frequency region (9.3GHz), Q-factor increases from 11,625GHz to 46,500GHz for BaTi4O9 ceramic doped with 1.0mol% Mn4+. The present paper reveals that the commonly observed degradation of dielectric properties due to coring effect in the BaTi4O9 ceramic system can be controlled by doping it with an appropriate quantity of Mn4+.

Development of Patch Antenna Substrate in BaO-4.TiO<sub>2</sub> System

BaTi4O9(BT4), has dielectric constant (εr)≈36 and unloaded Q-factor (Qf) >35,000GHz, but has temperature coefficient of frequency (τf~16-20ppm/°C). Ba2Ti9O20(B2T9), very near to BT4 in the BaO-TiO2 phase diagram, has εr~38, Qf~35,000GHz and τf<4ppm/°C. Though this phase is selected for most of the applications, there are many challenges like slow formation, decomposition, reaction with substrate etc. But, BT4 formed quickly and densified easily, but only high τf precluded it from many practical applications. Most of the literature on the modification of BT4 decreased the εr≤35. Here, the preparation and properties of ZnO/ZnTiO3 added BaTi4O9 ceramics are reported. The ceramics have been prepared by the solid state method. Raw materials have been homogenized and calcined at 1125°C. Calcined powders are ball-milled, compacted and sintered in 1275−1350°C to get dense ceramics with ρ=4.38-4.44 g/cc (TD>97.5%). XRD analysis has confirmed the BaTi4O9 phase formation along with secondary phases. FeSEM microstructures show liquid phase assisted sintering leading to fused grains and exaggerated grain growth. The dielectric properties have been measured near 4GHz by standard rod resonator methods using cylindrical specimens. The ceramics have εr36.5−38, τf<11ppm/°C and Qf>17THz. It is possible to further improve the Qf of these ceramics by controlling the processing.

Measuring the frequency-dependent dielectric properties of microwave composites using simple measurement methods

BaTi4O9 (BT4) ceramic was sintered at 1270°C and ground into fine ceramic powder with an average particle size of 3μm, then the BT4 powder was mixed with O-Cresol Novolac (OCN) epoxy resin to form epoxy-BT4 microwave composites. Using the plate method, the dielectric constants of the epoxy-BT4 microwave composites were measured from 100kHz to 100MHz at room temperature, then from 20°C to 140°C at 1MHz. The measured dielectric constants were fitted to the values predicted by the Lichtenecker equation. The dielectric constants of the epoxy-BT4 microwave composites were also measured from 1GHz to 10GHz at room temperature using the “square cavity resonator” method. In the GHz range, the dielectric constants of the composites were almost unchanged. It is conjectured that in both measurement frequency ranges, dielectric relaxation was nonexistent in both the BT4 ceramic powder and the epoxy-BT4 composites.

Electrical Properties of Amorphous BaTi4O9 Films Grown on Cu/Ti/SiO2/Si Substrates Using RF Magnetron Sputtering

Amorphous BaTi4O9 (BT4) films for use as capacitors embedded in PCB substrates were grown on Cu electrodes at low temperatures (≤ 200°C). The dielectric constant (k) of the amorphous BT4 film grown at room temperature (RT) was 38, and its dissipation factor was 3.2% at 100 kHz. A similar k value was obtained at radio‐frequency ranges, with a quality factor of 143 at 1.0 GHz. The films showed a capacitance density of 200 nF/cm2, a temperature coefficient of capacitance of 296 ppm/°C at 75 kHz, and a breakdown voltage of 42.5 V. This film therefore satisfies the requirements of the International Technology Roadmap for Semiconductors for 2016 for capacitors grown on organic substrates. In addition, the leakage current mechanism of the amorphous BT4 films was found to be Schottky emission, and the Schottky barrier height was calculated as 2.26 eV.

Phase evolution and electrical properties of copper-electroded BaTi4O9 materials with BaO–ZnO–B2O3–SiO2 glass system in reducing atmosphere

BaTi4O9 (BT4) microwave dielectric ceramics using a copper electrode and containing 10wt% BaO–ZnO–B2O3–SiO2 (BZBS) glass frit were sintered under reducing atmosphere at 950°C and were investigated on the phase evolutions, microstructures and dielectric properties of BT4 with various BaO/SiO2 and ZnO/SiO2 ratios of BZBS glasses. Experimental results show that the BaO/SiO2 ratio contributes to wettability of glass with BaTi4O9 ceramics, and ZnO/SiO2 ratio determines the densification of BaTi4O9 ceramics. The different Ba–Ti–O and Ba–Cu–O phases with various Ba/Ti and Ba/Cu ratios can be attributed to the contents of BaO in glass. Ba4Ti13O30 and Ba2Cu3O5+X may form when BaO contents are too high, and inducing copper diffusion due to the reactions of BaO and Cu, accompanying with degrading of the dielectric characteristics. If the ZnO contents of BZBS glasses were raised, a little bit of ZnSiO3 and Ba2Cu3O5+X phases appear without Cu diffusion due to non-reaction of ZnO and CuO. The high ZnO/SiO2 ratio of glass reveals the lower softening point, indicating that the high ZnO glass could enhance the density and therefore increase the dielectric constant and quality factor.

Effect of molecular weight of an anionic dispersant on the properties of BaTi4O9 slurries

The colloidal stability of BaTi4O9 (BT4) aqueous suspensions with poly(acrylamide-co-4-carboxylamino-4-oxo-2-butenate) (PAC) of different molecular weights at pH 9 has been investigated by means of zeta potential, adsorption, sedimentation, and particle size measurements. The results indicate that PAC could improve the dispersion of the particles from agglomeration. The resulting suspensions became more stabilized, and contained powder with smaller particle size. Consequently, the compacts with PAC exhibited better properties in terms of density and dielectric constant than those without any polymer present. The performance of PAC increased with decreasing polymer molecular weight. Clearly, PAC1 (Mw = 1.8 × 104) was most effective in dispersing the BT4 particles, and stabilizing the ceramic suspensions. This is attributed to the highest adsorption of this polymer onto BT4 powder, and causes strongest electrostatic repulsions among solid particles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

ChemInform Abstract: Chemical Design of Highly Water-Soluble Ti, Nb, and Ta Precursors for Multi-Component Oxides.

Novel citric acid based Ti, Nb and Ta precursors that are highly stable in the presence of water were developed. No alkoxides of Ti, Nb and Ta were utilized in the preparation, instead much less moisture-sensitive metallic Ti, NbCl5 and TaCl5 were chosen as starting chemicals for Ti, Nb and Ta, respectively. The feasibility of these chemicals as precursors is demonstrated in the powder synthesis of BaTi 4O9, Y3NbO7 and LiTaO3. The waterresistant Ti precursor was employed as a new source of water-soluble Ti in the amorphous citrate method, and phase pure BaTi4O9 in powdered form was successfully synthesized at 800 °C. The Pechini-type polymerizable complex method using the water-resistant Nb and Ta precursors was applied to the synthesis of Y 3NbO7 and LiTaO3, and both the powder materials in their pure form were successfully synthesized at reduced temperatures, viz. 500-700 °C. The remarkable retardation of hydrolysis of these water-resistant precursors is explained in terms of the partial charge model theory.

Low-fire Processing of Microwave BaTi4O9 Dielectric with BaO–Li2O–B2O3–SiO2–ZnO Glass

The effects of BaO–Li2O–B2O3–SiO2–ZnO (BLBSZ) glass addition on the densification and dielectric properties of BaTi4O9 (BT4) have been investigated. The microwave BT4 ceramics with 5–10 vol % BLBSZ glass can be densified at 900–925 °C, which is 400 °C lower than that required for pure BT4. The resulting microwave BT4+BLBSZ ceramics have a dielectric constant of 33–34, and the product (Q·fr) of the quality factor (Q) and resonant frequency ( fr) of 14,000–20,000 GHz at 6.6 GHz.

Measuring the microwave frequency relative permittivity of polyetherimide/BaTi4O9 composites by using a rectangular cavity resonator

In this paper, high glass transition temperature (Tg) of polyetherimide (PEI) is used to mix with different weight percent (0–80wt%) of BaTi4O9 (BT4) ceramic powder to form a flexible PEI/BT4 composite. The relative permittivity of PEI/BT4 composites is developed from 1to16GHz using the “rectangular cavity resonator” method. The relative permittivity of PEI/BT4 composites is calculated by observing the frequencies of resonant cavity modes. From the results of dielectric properties, the relative permittivity of PEI/BT4 composites is almost unchanged as the measured frequency is changed. It conjectures that the polarization mode does not exist in BT4 ceramic powder.

Electrical Properties of the Amorphous BaTi4O9 Thin Films for Metal-Insulator-Metal Capacitors

Amorphous BaTi4O9 (BT4) film was deposited on Pt/Si substrate by RF magnetron sputter and their dielectric properties and electrical properties are investigated. A cross sectional SEM image and AFM image of the surface of the amorphous BT4 film deposited at room temperature showed the film was grown well on the substrate. The amorphous BT4 film had a large dielectric constant of 32, which is similar to that of the crystalline BT4 film. The leakage current density of the BT4 film was low and a Poole-Frenkel emission was suggested as the leakage current mechanism. A positive quadratic voltage coefficient of capacitance (VCC) was obtained for the BT4 film with a thickness of<70 nm and it could be due to the free carrier relaxation. However, a negative quadratic VCC was obtained for the films with a thickness ≥96nm, possibly due to the dipolar relaxation. The 55 nm-thick BT4 film had a high capacitance density of 5.1fF/μm2 with a low leakage current density of 11.6nA/cm2 at 2 V. Its quadratic and linear VCCs were 244ppm/V2 and -52 ppm/V, respectively, with a low temperature coefficient of capacitance of 961ppm/˚C at 100 kHz. These results confirmed the potential suitability of the amorphous BT4 film for use as a high performance metal-insulator-metal (MIM) capacitor.

Preparation and Structure of Ba&lt;sub&gt;2&lt;/sub&gt;Ti&lt;sub&gt;9&lt;/sub&gt;O&lt;sub&gt;20&lt;/sub&gt; and BaTi&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;9&lt;/sub&gt; Ceramics Derived from Sol-Gel Powders

Ba2Ti9O20 (B2T9) and BaTi4O9 (BT4) ceramics have been fabricated using sol-gel technique. The sol-gel derived powder was produced from barium acetate and butyl titanate using acetic acid as solvent. The as-prepared powders were then calcined at different temperatures ranging from 600° to 1200°C. After that, the powder was pressed into pellets and further sintered at different temperatures ranging from 1250°C to 1380°C. XRD characterization and Raman spectroscopy showed that after calcining the sol-gel powder at 900°C for 2 h and sintering the pressed pellets at 1330°C for 4 h, triclinic B2T9 and orthorhombic BT4 ceramics could be obtained. The dielectric constant and Q-value are 35 and 1910 at 6.1 GHz.

Low‐Fire Processing of Microwave BaTi4O9Dielectric with BaO–ZnO–B2O3Glass

The effects of BaO—ZnO–B2O3(BZB) glass addition on the densification and dielectric properties of BaTi4O9(BT4) have been investigated. With increasing BaO content in the BZB glass, the softening and melting points of the resulting BZB glass decrease, but the wetting between BZB and BT4 improves cosiderably. Although the densification temperature is reduced from 1300°C for pure BT4 to 925°C for BT4+BZB dielectric ceramics, the enhancement in densification becomes less significant with increasing BaO content in the BZB glass. The above result is attributed to a chemical reaction taking place at the interface of BZB/BT4 during firing, which becomes less extensive with increasing BaO content in the BZB glass. For the BZB glass with a BaO content in the range of 0–20 mol%, the resulting 90 vol% BT4+10 vol% BZB microwave dielectric has a dielectric constant of 28–33, and a product (Q×fr) of quality factor (Q) and a resonant frequency (fr) of 15 000–20 000 GHz at 6.6 GHz.

Dielectric Degradation and Microstructures of Heterogeneous Interfaces in Cofired Multilayer Ceramic Capacitors

The compatibility of electrodes and dielectrics in cofired MLCCs with both Ni and Ag/Pd electrodes was characterized by transmission electron microscopy (TEM) using tripod polished samples. Tripod polishing procedures can reduce entire devices to a thickness of less than 1 μm. After low angle ion milling for a short time, many regions across several dielectric and electrode layers are electron transparent, which makes it possible to characterize the cofired interfacial microstructures. When analyzed by convergent beam electron diffraction (CBED) and energy dispersive X-ray spectrometry (EDS), NiO lamellae and P-rich intermediate layers were found in highly accelerated life tested (HALT) MLCCs with Ni electrodes. CBED confirmed that the P-rich layers had a Ba4Ti13O30 (B4T13) structures. Oxidized Ni layers containing Mn were also found in the HALT samples. It is believed that Mn ions were reduced by the Ni electrodes, as P-rich and Mn-rich segregated layers were observed in the virginal non-life tested MLCCs. Grains with stacking faults, containing dopants such as Mn, Si, and Mg, had the BaTi4O9 (BT4) structure. No silver diffusion was found in either the BaTiO3 based perovskite lattices or the flux phases in air-fired X7R type MLCCs.

Effects of RuO2 dispersion on photocatalytic activity for water decomposition of BaTi4O9 with a pentagonal prism tunnel and K2Ti4O9 with a zigzag layer structure

Effects of RuO2 dispersion on the photocatalytic activity for water decomposition of BaTi4O9 (BTO) with a pentagonal prism tunnel structure and K2Ti4O9 (KTO) with a zigzag layer structure were studied. These titanates were impregnated with either a RuCl3 aqueous solution or a Ru3(CO)12 complex in THF and were subjected to oxidation at high temperatures. In comparison with the chloride, the employment of Ru3(CO)12 complex gave rise to the higher photocatalytic activity of BTO and a significant improvement of photocatalytic performance of KTO. High resolution transmission electron microscopic observation showed that the carbonyl complex led to the formation of uniformly distributed small RuO2 particles (average particle size, ρav, was 1.8 nm for BTO and 5.1 nm for KTO) than did the chloride (ρav was 2.7 for BTO and 15 nm for KTO). The tunnel structure of BTO is shown to have the high capability to disperse RuO2 as small particles, compared to the zigzag layer. The photoexcited charge formation of KTO with UV irradiation was examined by electron paramagentic resonance (EPR) measurements. A correlation between the photocatalytic activity and the ability of surface lattice O− formation is established for these titanates with different structures. The size effects of RuO2 particles on photocatalysis are discussed.