Preparation and properties of low-temperature co-fired ceramic of CaO–SiO2–B2O3 system

Low temperature co-fired ceramic (LTCC) was prepared by sintering a glass selected from CaO–SiO₂–B₂O₃ system, in which 0.5 wt% P₂O₅ and 0.5 wt% ZnO were added to optimize the preparation conditions. The glass powder and sintered bodies were characterized by different analytical techniques such as TG-DTA analysis, X-ray diffraction and Scanning electron microscopy. It was found that the optimal sintering temperature was 820°C based on the microstructure and the properties of sintering bodies, and then the major phases of the LTCC were CaSiO₃, CaB₂O₄ and SiO₂. The obtained products, with dielectric constant about 6.5, dielectric loss about 2 × 10⁻³ at 30 MHz and coefficient of thermal expansion about 8 × 10⁻⁶ °C⁻¹ between 20 and 400°C, are supposed to be suitable for application in wireless communications.     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

Effect of the ion beam current density on the formation of implanted metal nanoparticles in a dielectric matrix

The effect of the ion beam current density, varied within 4–15 μA/cm², on the formation of metal nanoparticles in a subsurface layer of SiO² substrates implanted with 30-keV Ag⁺ ions to a dose of 5×10 16 cm⁻² was studied by optical spectroscopy and atomic force microscopy techniques. An increase in the ion beam current density leads to the formation of nanoparticles of a greater size as a result of the glass substrate heating and due to an increase in the diffusion mobility of implanted silver atoms. These results suggest the possibility of controlling the dimensions of implanted nanoparticles in dielectrics by means of variation of the ion beam current density during the process.     

The comparative influences of structural ordering, grain size, Li-content, and bulk density on the Li+-conductivity of Li0.29La0.57TiO3

The lattice and total Li⁺-ionic conductivity of Li_0.29La_0.57TiO₃ ceramic (LLTO) sintered at 1200 °C were determined as functions of powder calcination temperature and sintering duration, and these results were correlated with the relative degrees of Li⁺-ordering, Li-content, grain size, and bulk density to assess the relative impact of these parameters on material performance. Under all conditions, LLTO formed with a high degree of tetragonal superstructure to its perovskite related framework, and the lattice conductivity closely followed the relative amounts of the superstructure, as evaluated via determination of the sample ordering parameter from X-ray diffraction data. LLTO powders that were calcined at 900 °C for 1 h and sintered at 1200 °C for 6 h gave lattice conductivity values (~1.14 × 10⁻³ S cm⁻¹) comparable within the highest ranges reported in the literature. This coincided with the lowest degree of tetragonal superstructure formation, and it was also found to be largely independent of the values of Li-content measured on sintered ceramic despite significant Li₂O volatilization at longer sintering times (up to 23 % after 12 h at 1200 °C). Samples of LLTO powder that were calcined at 1100 °C and sintered at 1200 °C for 12 h resulted in the highest total Li-ion conductivity value ~6.30 × 10⁻⁵ S cm⁻¹. The total conductivity of LLTO varied inversely with grain size when the grains were <20 μm but was insensitive to that parameter above that size threshold. The strongest influence on total conductivity was primarily the bulk ceramic density. It was estimated from measured values that as the bulk ceramic density approached the full theoretical value for LLTO the total conductivity could near the lattice conductivity of ~1.2 × 10⁻³ S cm⁻¹.     

Microwave dielectric properties of Ba2Ti3Nb4O18 ceramic doped with ZnO–B2O3–SiO2 glass and its compatibility with silver electrode

The effects of ZnO–B₂O₃–SiO₂ glass (ZBS) additions on the sintering behavior and microwave dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramic have been investigated. Due to the liquid phase effects resulting from the additives, the addition of ZBS glass can reduce the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramic from 1,250 to 925 °C and induce no obvious degradation of the microwave dielectric properties. Typically, when 3wt% ZBS is added, a dense ceramic can be sintered at 925 °C with a ε_r of 33.2, a high of Q × f of 13,600 GHz and a low τ _f of −5.9 ppm/°C. Moreover, ZBS glass-added Ba₂Ti₃Nb₄O₁₈ ceramic has a chemical compatibility with silver electrode, which suggests that the ceramic could be applied to LTCC devices application.     

Electrical and thermal conductivities of porous SiC/SiO2/C composites with different morphology from carbonized wood

Porous SiC/SiO₂/C composites exhibiting a wide range of high thermal and electrical conductivities were developed from carbonized wood infiltrated with SiO₂. As a pre-treatment, the samples were either heated at 100 °C or kept at room temperature followed by sintering in the temperature range 1200–1800 °C. The microstructure, the morphology, and the electrical and thermal conductivities of the composites were investigated. Pre-treatment at room temperature followed by sintering up to 1800 °C produced composites exhibiting a greater size of carbon crystallites, a higher ordering of the microstructure of carbon and β-SiC and a smaller amount of SiO₂, resulting in electrical and thermal conductivities of 1.17 × 10⁴ Ω⁻¹ m⁻¹ and 25 W/mK, respectively. The thermal conductivity could be further improved to 101 W/mK by increasing the density of the composite to 1.82 g/cm³. In contrast, the pre-treatment at 100 °C produced composites possessing a lower thermal conductivity of 2 W/mK.     

Microstructure and microwave dielectric characteristics of CaO–B2O3–SiO2 glass ceramics

CaO–B₂O₃–SiO₂ (CBS) glass powders are prepared by traditional glass melting method, whose properties and microstructures are characterized by Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the pure CBS glass ceramics possess excellent dielectric properties (ε _r = 6.5, tan δ = 5 × 10⁻³ at 10 GHz), but a higher sintering temperature (>900 °C) and a narrow sintering temperature range (about 10 °C). The addition of a low-melting-point CaO–B₂O₃–SiO₂ glass (LG) could greatly decrease the sintering temperature of CBS glass to 820 °C and significantly enlarge the sintering temperature range to 40 °C. The CBS glass ceramic with 30 wt% LG glass addition sintered at 840 °C exhibits better dielectric properties: ε _r ≈ 6, tan δ < 2 × 10⁻³ at 10 GHz, and the major phases of the sample are CaSiO₃, CaB₂O₄ and SiO₂.     

Monodisperse nickel nanoparticles supported on SiO<Subscript>2</Subscript> as an effective catalyst for the hydrolysis of ammonia-borane

Monodisperse Ni nanoparticles (NPs) have been synthesized by the reduction of nickel(II) acetylacetonate with the borane-tributylamine complex in a mixture of oleylamine and oleic acid. These Ni NPs are an active catalyst for the hydrolysis of the ammonia-borane (AB, H₃N·BH₃) complex under ambient conditions and their activities are dependent on the chemical nature of the oxide support that they were deposited on. Among various oxides (SiO₂, Al₂O₃, and CeO₂) tested, SiO₂ was found to enhance Ni NP catalytic activity due to the etching of the 3.2 nm Ni NPs giving Ni(II) ions and the subsequent reduction of Ni(II) that led to the formation of 1.6 nm Ni NPs on the SiO₂ surface. The kinetics of the hydrolysis of AB catalyzed by Ni/SiO₂ was shown to be dependent on catalyst and substrate concentration as well as temperature. The Ni/SiO₂ catalyst has a turnover frequency (TOF) of 13.2 mol H₂·(mol Ni)⁻¹ · min⁻¹—the best ever reported for the hydrolysis of AB using a nickel catalyst, an activation energy of 34 kJ/mol ± 2 kJ/mol and a total turnover number of 15,400 in the hydrolysis of AB. It is a promising candidate to replace noble metals for catalyzing AB hydrolysis and for hydrogen generation under ambient conditions.     

Influence of sputtering power on the physical properties of magnetron sputtered molybdenum oxide films

Thin films of molybdenum oxide were formed on glass and silicon substrates by sputtering of molybdenum target under various sputtering powers in the range 2.3–6.8 W/cm², at a constant oxygen partial pressure of 2 × 10⁻⁴ mbar and substrate temperature 523 K employing DC magnetron sputtering technique. The effect of sputtering power on the core level binding energies, chemical binding configurations, crystallographic structure, surface morphology and electrical and optical properties was systematically studied. X-ray photoelectron spectroscopic studies revealed that the films formed at sputtering powers less than 5.7 W/cm² were mixed oxidation states of Mo⁵⁺ and Mo⁶⁺. The films formed at 5.7 W/cm² contained the oxidation state Mo⁶⁺ of MoO₃. Fourier transform infrared spectra contained the characteristic optical vibrations. The presence of a sharp absorption band at 1,000 cm⁻¹ in the case of the films formed at 5.7 W/cm² was also conformed the existence of α-phase MoO₃. X-ray diffraction studies also confirmed that the films formed at sputtering powers less than 5.7 W/cm² showed the mixed phase of α-and β-phase of MoO₃ where as at sputtering power of 5.7 W/cm² showed single phase α-MoO₃. The electrical conductivity of the films increased from 8 × 10⁻⁶ to 1.2 × 10⁻⁴ Ω⁻¹ cm⁻¹, the optical band gap decreased from 3.28 to 3.12 eV and the refractive index decreased from 2.12 to 1.94 with the increase of sputtering power from 2.3 to 6.8 W/cm², respectively.     

Preparation and characterizations of tungsten oxide electrochromic nanomaterials

Nanoscaled tungsten oxide thin films were fabricated by galvanostatic electrodeposition. The effect of preparation parameters such as tungsten ions concentration, pH, current density and annealing on the properties and performance of WO₃ thin films electrochromic materials was investigated. XRD, SEM–EDS, TEM, FTIR, UV–VIS spectrophotometry, and electrochemical measurements were utilized to characterize the structural and compositional properties as well as the electrochromic behaviour of the prepared thin films. Triclinic WO₃ structure was prepared at 0.1 M W⁺ and current density of 0.5 mA cm⁻², while at 0.2 M W⁺ and 1 mA cm⁻², orthorhombic structure was revealed. High energy gap of 3.5 eV with diffusion coefficient of 6.81 × 10⁻¹¹ cm² S⁻¹ and coloration efficiency of 62.68 cm² C⁻¹ were obtained for the films prepared at pH 2, 1 mA cm⁻², and 0.1 M W⁺.     

High-temperature oxidation of MoSi<Subscript>2</Subscript>

Oxidation behavior of MoSi₂ was investigated in air over the temperature range of 1400–1700 °C. Spallation of the SiO₂ scale did not occur at any temperature, and Mo₅Si₃ formation did not happen below 1700 °C. A change in the rate-controlling mechanism was detected within the temperature range of this study. Activation energy for oxidation of MoSi₂ at high temperatures was determined to be 204 kJ/mol. This value is less than the value of activation energy for oxidation of MoSi₂ controlled by diffusion of O₂ through amorphous SiO₂ layer reported at lower temperatures. The decrease in activation energy is attributed to the increased degree of crystallization of amorphous silica to β-cristobalite at high temperatures resulting in enhanced O₂ diffusion through SiO₄⁻⁴ tetrahedral structure.     

Sintering and electrical properties of Ce<Subscript>0.8</Subscript>Sm<Subscript>0.2</Subscript>O<Subscript>1.9</Subscript> film prepared by spray pyrolysis and tape casting

Ce_0.8Sm_0.2O_1.9 (SDC) powder was synthesized by spray pyrolysis at 650 °C. XRD results showed that phase-pure SDC powder with an average crystallite size of 11 nm was synthesized. SDC electrolyte film was prepared by tape casting and sintered at different temperatures of 1,300, 1,400 and 1,500 °C for 2 h, respectively. The SDC electrolyte film was relatively denser and showed finer microstructure at relatively lower temperature of 1,400 °C, which might be due to the high sintering activity of the spray pyrolysis SDC powder. The ionic conductivity of the SDC electrolyte film sintered at 1,400 °C reached a maximum value of 9.5 × 10⁻³ S cm⁻¹ (tested at 600 °C) with an activation energy for conduction of 0.90 eV.     

Sintering and electromagnetic properties of BaFe12O19 ferrite prepared by co-precipitation method

BaFe₁₂O₁₉ (BaM) was synthesized through the co-precipitation route. Pure phase BaM was formed after calcination of precipitated powder at 900 °C. BaM was sintered at three different temperatures; 1100, 1200, and 1300 °C to study the sintering kinetics by varying the sintering time from 1 to 4 h. Apparent porosity decreased, and bulk density increased with increasing sintering temperature and period. A bulk density of about 4.6 g/cm³ was achieved after sintering at 1300 °C/4 h. The rate-controlling mechanism of BaM densification was the diffusion of oxygen, and the activation energy for the sintering process was 274 kJ/mol. The grain size of BaM increased with rising sintering temperatures. Permittivity increased from about 11 to 17 and the permeability increased from about 10 to 16 with the increase in sintering temperature from 1100 to 1300 °C. Saturation magnetization was also enhanced to about 69 emu/g after sintering at 1300 °C/4 h. Therefore, BaM ferrite synthesized through the co-precipitation route can be effectively used for high-frequency applications after sintering at 1300 °C.

     

Epitaxial growth of thin gold films onto pure and doped NaCl and KCl substrates

The influence of impurities such as calcium, strontium or silver ions present in the substrates on the structural growth features of continuous gold thin films, vacuum evaporated at constant deposition rates onto NaCl and KCl substrates heated in the temperature range from 90 to 300 °C, was studied by transmission electron microscopy and transmission electron diffraction. The epitaxial growth of gold thin films is inhibited by the presence of 5 × 10^-1 mol.% strontium or calcium ions in the KCl and NaCl substrates. The presence of 1.7 × 10^-1 mol.% silver ions in the NaCl substrates enhances the epitaxial growth of the gold thin films even at a substrate temperature of 120 °C. An enhancement of the gold thin film epitaxial growth is also obtained with NaCl-2 × 10^-2mol.%Ag-5 × 10^-1mol.%Ca and NaCl-1.7 × 10^-1mol.%Ag-5 × 10^-1mol.%Ca substrates.     

Effect of B2O3 and CuO additions on the sintering temperature and microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics

The effects of B₂O₃–CuO (BCu, the weight ratio of B₂O₃ to CuO is 1:1) addition on the sintering behavior, microstructure, and the microwave dielectric properties of 3Li₂O–Nb₂O₅–3TiO₂ (LNT) ceramics have been investigated. The low-amount addition of BCu can effectively lower the sintering temperature of LNT ceramics from 1125 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 2 wt% BCu-added ceramic sintered at 900 °C has better microwave dielectric properties of ε _r  = 50.1, Q × f = 8300 GHz, τ _f  = 35 ppm/°C. Silver powders were cofired with the dielectric under air atmosphere at 900 °C. The SEM and EDS analysis showed no reaction between the dielectric ceramic and silver powders. This result shows that the LNT dielectric materials are good candidates for LTCC applications with silver electrode.     

Synthesized silicon-substituted hydroxyapatite coating on titanium substrate by electrochemical deposition

Silicon-substituted hydroxyapaptite (Si-HA) coatings were prepared on titanium substrates by electrolytic deposition technique in electrolytes containing Ca²⁺, PO₄ ³⁻ and SiO₃ ²⁻ ions with various SiO₃ ²⁻/(PO₄ ³⁻ + SiO₃ ²⁻) molar ratios(η_si). The deposition was all conducted at a constant voltage of 3.0 V, with titanium substrate as cathode and platinum as anode, for 1 h at 85°C. The coatings thus prepared were characterized with inductively coupled plasma (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field-emission-type scanning electron microscope (FSEM). The results show that the silicon amount in the coatings increases linearly to about 0.48 wt% at first with increasing η_si between 0 and 0.03, then increases slowly to about 0.55 wt% between 0.03 and 0.10 and finally maintains almost at a level around 0.55 wt% between 0.10 and 0.30. The tree-like Si-HA crystals are observed in the coatings prepared in the electrolyte of η_si = 0.20. And the presence of silicon in electrolytes decreases the thickness of the coatings, with effect being more significant as η_si increased. Additionally, the substitution of Si causes some OH⁻ loss and changes the lattice parameters of hydroxyapatite (HA).     

Synthesis and characterization of Al2?xScx(WO4)3 ceramics for low-expansion infrared-transmitting windows

A low thermal-expansion material was synthesized with potential application in thermal-shock-resistant infrared-transmitting windows. The material is derived from a solid solution of Al₂(WO₄)₃, which has positive thermal expansion, and Sc₂(WO₄)₃ with a negative thermal expansion. An optimum composition of Al_0.5Sc_1.5(WO₄)₃ was identified by synthesizing solid solutions, Al_2−x Sc _x (WO₄)₃, by a solid-state route with compositions ranging from x = 0 to 2.0. A single orthorhombic phase was obtained at all compositions. A composition corresponding to x = 1.5 had a low coefficient of thermal expansion of −0.15 × 10⁻⁶/°C in the temperature range 25–700 °C. A low temperature solution combustion process was developed for this optimum composition, resulting in a single-phase powder with a surface area of ~14 m²/g and average particle size (as determined from surface area) of 92 nm. The powder was consolidated by slip-casting, sintering, and hot-isostatic pressing into visibly translucent disks with a peak in-line transmittance of 73 % at 2300 cm⁻¹. Significant infrared absorption in a 1-mm-thick disk of this material begins near 2200 cm⁻¹ and features three absorptions arising from 2-phonon transitions at 2002, 1847, and 1676 cm⁻¹. The infrared and Raman spectra are interpreted in terms of 1-, 2-, and 3-phonon vibrational transitions.     

The effect of MgO and SiO2 codoping on the properties of Nd:YAG transparent ceramic

Nd:YAG transparent ceramics were fabricated by a reactive sintering method under vacuum using SiO₂, MgO and compound additives (SiO₂ and MgO) as sintering aids. The effects of SiO₂ and MgO on the microstructure and sintering process of Nd:YAG ceramics were studied. High quality Nd:YAG ceramics with compound sintering aids obtained by vacuum sintering at 1780 °C are composed of grains of the size ∼10 μm, and their transmittance is 82% at 400 nm. It was found the absorption coefficient of 1.0 mol% Nd:YAG ceramic was 8.6 cm⁻¹ at 808 nm and its absorption cross section was calculated to be 6.26 × 10⁻²⁰ cm².     

Pressureless sintering curve and sintering activation energy of Fe–Co–Cu pre-alloyed powders

The kinetic characteristics of Fe–Co–Cu pre-alloyed powders in the pressureless sintering process have been investigated. The expansion ratio, linear shrinkage, densification rate and effect of heating rate on the sintering have been analyzed. Based on the classical Arrhenius curve, the sintering activation energy has been calculated. Results show that the samples have a smaller expansion ratio before contracting when the Fe content is higher, and the final linear shrinkage ratio is larger too. The sintering carries out more efficiently and the final linear shrinkage ratio is larger when the samples at a lower heating rate. In the initial and final stage of sintering, the Arrhenius curve is suitable for the Fe–Co–Cu pre-alloyed powders and diffusion is the main transport mechanism. At the initial stage of sintering the sintering activation energy of Fe25%–Co15%–Cu60% powder is 453.11 kJ/mol, Fe45%–Co15%–Cu40% powder is 638.28 kJ/mol and Fe65%–Co15%–Cu20% powder is 504.6 kJ/mol, respectively. At the final stage of sintering the sintering activation energy of Fe25%–Co15%–Cu60% powder is 31.17 kJ/mol, Fe45%–Co15%–Cu40% powder is 20.09 kJ/mol and Fe65%–Co15%–Cu20% powder is 35.13 kJ/mol, respectively. The sintering activation energy in the middle stage is dominated by not only one diffusion mechanism so it is not suitable for the Arrhenius curve.     

Effect of sintering process on electrical properties and ageing behavior of ZnO–V2O5–MnO2–Nb2O5 varistor ceramics

The effect of sintering process on microstructure, electrical properties, and ageing behavior of ZnO–V₂O₅–MnO₂–Nb₂O₅ (ZVMN) varistor ceramics was investigated at 875–950 °C. The sintered density decreased from 5.52 to 5.44 g/cm³ and the average grain size increased from 4.4 to 9.6 μm with the increase of sintering temperature. The breakdown field (E_{1 mA}) decreased from 6991 to 943 V/cm with the increase of sintering temperature. The ZVMN varistor ceramics sintered at 900 °C led to surprisingly high nonlinear coefficient (α = 50). The donor concentration (N_d) increased from 3.33 × 10¹⁷ cm⁻³ to 7.64 × 10¹⁷ cm⁻³ with the increase of sintering temperature and the barrier height (Φ_b) exhibited the maximum value (1.07 eV) at 900 °C. Concerning stability, the varistors sintered at 925 °C exhibited the most stable accelerated ageing characteristics, with %ΔE_{1 mA} = 1.5% and %Δα = 13.3% for DC accelerated ageing stress of 0.85 E_{1 mA}/85 °C/24 h.