Spherical shape Ba-based glass powders prepared by spray pyrolysis for MLCCs

Spherical shape BaO–B₂O₃–SiO₂ glass powders were directly prepared by high temperature spray pyrolysis at >1000 °C. The thermal and morphological characteristics of the prepared glass powders were investigated. The glass powders prepared at temperature of 1000 °C had spherical shape and hollow inner structure. On the other hand, the powders prepared at high temperature of 1300 °C had complete spherical shape and dense inner structure by complete melting. The mean size of the glass powders was 0.9 μm. The glass transition temperatures (T _g) of the glass powders obtained by spray pyrolysis at preparation temperatures between 1000 and 1300 °C were 601.1 °C regardless of the preparation temperatures. The specimen of the glass powders obtained by spray pyrolysis at the preparation temperature of 1300 °C had small number of voids even at low sintering temperature of 700 °C. In addition, the specimen sintered at temperature of 800 °C had dense microstructure without voids.     

Colloidal spray pyrolysis preparation and characterization of nanocrystalline NiO-SDC composite powders for SOFCs

The nanocrystalline NiO-Ce_0.8Sm_0.2O_1.9 (NiO-SDC) composite powders were prepared by colloidal spray pyrolysis. The morphological characteristics, particle size and distribution of the particles obtained from calcining spray pyrolysis derived powders were investigated. The results showed that: The composite powders from spray colloidal solutions with Ni hydroxy carbonate sols were better than those with Ce-Sm hydroxy carbonate sols in crystallinity and primary particle size. The powders had a very narrow particle size distribution centered at 250 nm in which NiO and SDC primary particles were distributed homogenously. The composite powders could favor the formation of high performance anodes of SOFCs.     

Synthesis of nanosized (1 − x)BiScO3 − xPbTiO3 ferroelectric ceramic powders

Nanosized (1???x)BiScO₃???xPbTiO₃ ferroelectric ceramic powders was obtained by the metal citrate sol–gel method. The decomposition process of the polymer was studied by using infrared spectral absorption and X-ray diffraction. Perovskite phase can be obtained at the calcining temperature as low as 450 °C and the average grain sizes of powders were calculated by XRD method. The influence of the grain size by pH value of the solution is explained. The calcining temperature is proved to be the foremost factor to determine the grain size which grew from 12 to 23 nm when calcined at different temperatures. The holding time can also affect the grain size. The sintering temperature can be reduced by 100 °C using nano powders than using traditionally prepared large grain powders.     

Low-temperature sintering of BaTiO3 with Mn-Si-O glass

In order to reduce sintering temperature and prevent adverse dielectric effects, pure BaTiO₃ powder with the addition of Mn-Si-O glass was sintered in the temperature range of 1175–1300°C. Microstructural observation showed that BaTiO₃ grains of the sintered samples only grew from the initial 400 nm to an average of 430 nm between 1175–1275°C for 1 h, or sintered at 1250°C as long as 27 h. Abnormal BaTiO₃ grains are not found in the sintered samples. The microstructure and phase analysis showed that the dielectric properties, tetragonality, and grain growth of BaTiO₃ are closely controlled by the formation of the liquid phase, newly formed Ba₂TiSi₂O₈ grains, and Mn solid solution in BaTiO₃ grains.     

Flame spray synthesis and characterisation of stabilised ZrO2 and CeO2 electrolyte nanopowders for SOFC applications at intermediate temperatures

Zirconia (Y_0.16Zr_0.84O₂, Sc_0.2Zr_0.8O₂ and Sc_0.2Ce_0.01Zr_0.79O₂) and ceria (Gd_0.2Ce_0.8O₂) based electrolyte materials are synthesised at production rates up to 260 g h^?1 by a liquid-fed one-step flame spray synthesis from water-based solutions, or cost-effective rare earth nitrates with a high water content. It was found that this one-step synthesis, based on an acetylene-supported flame is able to produce phase pure and highly crystalline, nanoscale electrolyte materials. The as-synthesised powders show a cubic lattice structure independent of production rates. Specific surface areas of the powders were adjusted between 20 and 60 m² g^?2, where the latter is an upper limit for the further processing of the powders in terms of screen printing. The influence of process parameters on morphology, particle size, composition, crystallinity, lattice parameter, shrinkage behaviour and coefficient of thermal expansion of the as-synthesised powders were systematically investigated by transmission electron microscopy (TEM), nitrogen adsorption (BET), X-ray diffraction (XRD) and dilatometry. Electrochemical impedance spectroscopy (EIS) was applied at temperatures between 300 °C and 900 °C and confirmed the high quality and the competitive electrochemical behaviour of the produced powders.     

Microstructure and dielectric properties of ferroelectric barium strontium titanate ceramics prepared by hydrothermal method

Ba _x Sr_1-x TiO₃, nanoparticles with different Ba compositions were synthesized by a hydrothermal method. The mechanism of hydrothermal reactions was discussed based on DTA/TG, XRD and TEM characterizations. The result showed that perovskite structure was developed through the mutual diffusion between the intermediate phases and TiO₂ phase. The grain size of the Ba_0.77Sr_0.23TiO₃ (BST77) powders was about 20–40 nm. BST ceramics were made from the hydrothermal-derived BST powders and the dielectric properties of the BST ceramics were measured. Due to the small grain size and active surface energy of the BST powders prepared by hydrothermal method, the BST ceramics showed low sintering temperature. It was found that the BST77 ceramics sintered at 1280 °C showed dielectric constant peak dispersion which was believed to be caused by dimension domino effect.     

Photoluminescence characteristics of Y3Al5O12:Tb3+ phosphors synthesized using the combustion method

For this study, terbium-doped yttrium aluminum garnet (YAG:Tb) phosphor powders were prepared via the combustion process using the 1:1 ratio of metal ions to reagents. The characteristics of the synthesized nano powder were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and photoluminescence. Single-phase cubic YAG:Tb crystalline powder was obtained at 800 °C by directly crystallizing it from amorphous materials, as determined by XRD techniques. There were no intermediate phases such as yttrium aluminum perovskite (YAlO₃) and yttrium aluminum monoclinic (Y₄Al₂O₉) observed in the sintering process. The SEM image showed that the resulting YAG:Tb powders had uniform sizes and good homogeneity. With the increase in the sintering temperature, the grain size increased. The photoluminescence spectra of the YAG:Tb nanoparticles were investigated to determine the energy level of electron transition related to luminescence processes. There were three peaks in the excited spectrum, and the major one was a broad band of around 274 nm. Also, the YAG:Tb nanoparticles showed two emission peaks in the range of 450?×?500 and 525?×?560 nm, respectively, and had maximum intensity at 545 nm.     

Size dependence of THz region dielectric properties for barium titanate fine particles

Barium titanate (BaTiO₃) crystallites with various particle sizes from 22 to 500 nm were prepared by the two-step thermal decomposition method of barium titanyl oxalate. Various characterizations revealed that these particles were impurity-free, defect-free, dense BaTiO₃ particles. The powder dielectric measurement clarified that the dielectric constant of BaTiO₃ particles with a size of around 58 nm exhibited a maximum of over 15,000. To explain this size dependence, the THz region dielectric properties of BaTiO₃ fine particles, especially Slater mode frequency, were measured using the far infrared (FIR) reflection method. As the result, the lowest Slater mode frequency was obtained at 58 nm. This tendency was completely consistent with particle size dependence of the dielectric constant.     

The co-fired behaviors between Ag and glass–ceramics materials in LTCC

The paper studied the interfacial co-fired behavior between silver and Ba–Ti–B–Si–O glass–ceramics composites for LTCC application. The dielectric properties of this LTCC glass–ceramic materials were as follows: ??≈?8–10, tanδ?≤?2?×?10^?3 (at 1 GHz), and its sintering temperature was lower than 900 °C. The Ag elemental distribution near the interface between glass–ceramics and Ag was investigated by scanning electronic microscopy and energy spectrum analysis. No de-lamination, camber and cracking were found between LTCC/Ag systems after firing at 810–900 °C for 2 h. The experimental results showed that the diffusion of silver was mainly decided by sintering temperature and microstructure of LTCC. Promoting densification of the LTCC can prevent Ag diffusion from co-fired interface.     

Characteristics of silver powders synthesized from silver 2-ethylhexanoate and Di-n-octylamine

Uniform spherical submicron silver powders were synthesized from a long-chain alkyl carboxylate of silver 2-ethylhexanoate and an alkylamine of di-n-octylamine in this study. The decomposition of silver 2-ethylhexanoate was observed to accelerate significantly in the presence of di-n-octylamine. SEM results revealed that submicron silver powders with sizes ranging from 200 nm to 300 nm and a high tap density of 4.0 g/cm³ were successfully prepared at 150 °C for 3 h in air. TGA reveals that approximately 1.2 wt.% organic residues composed mainly of 2-ethylhexanoate with a slight amount of di-n-octylamine were attached to the silver particles, as confirmed by the FTIR and XPS results. To evaluate the feasibility for practical applications, silver paste prepared from the silver powders synthesized in this study (NAG 80 paste) was examined and characterized, and the results were compared with those of two commercially available powders (SF80 and GH67 pastes). The electrical resistivities of the NAG80 films fired at 300 and 500 °C respectively read 1.8?×?10^?5?Ω-cm and 1.1?×?10^?5?Ω-cm, both superior to those of the SF80 and GH67 films. The fine quality of the uniform submicron spherical silver powders was verified and its potential use in thick film conductors confirmed.     

Characterization of PT ferroelectric thin films on porous silica for pyroelectric IR detectors

Ferroelectric PbTiO₃ thin films were deposited on Pt/DS/PS/SiO₂/Si substrates by sol–gel technique. Porous silica (PS) thin film was used as thermal-insulation layer and dense silica (DS) thin film was a buffer layer to reduce surface roughness of PS layer. Root mean square surface roughness can be effectively reduced from 9.7 to 3.5 nm after PS buffer layer was prepared. The average grain size of PT thin films decreased slightly with increasing thickness of porous silica. Dielectric constant of PT increased from 107 to 171 at 1 KHz as thickness of PS layer increased from 0 to 2,000 nm. PT thin film prepared on 2,000 nm porous silica exhibited good dielectric property. The leakage current density was less than 1.6?×?10^-6 A/cm² when the applied electrical field was 200 kV/cm. The composite film is suitable for preparing pyroelectric IR detectors.     

Enhancement in the physical properties of K0.5Na0.5NbO3 ceramics by the addition of 0.5 Li2O – 0.5K2O – 2B2O3 glass

The addition of powdered 0.5 Li₂O–0.5K₂O–2B₂O₃ (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K_0.5Na_0.5NbO₃ (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (?_r) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d₃₃) was found to be 130 pC/N for 1 wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of P_r with the increase in glass content, the P_r values were higher than that obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size.     

Influence of fillers on the re-crystallization and dielectric properties of 60ZnO-30B<Subscript>2</Subscript>O<Subscript>3</Subscript>-10SiO<Subscript>2</Subscript> glass

This paper reports re-crystallization behaviour of 60ZnO-30B₂O₃-10SiO₂ pure glass. Influence of different fillers on the re-crystallization is also highlighted. Irrespective of the nature of the filler, glass transition temperature (T_g) remains the same as that of the pure glass at 570 °C. The onset crystallization temperature is enhanced by 15 to 25 °C owing to filler addition. The peak crystallization temperature corresponding to Zn₃B₂O₆, ZnB₂O₄ and willemite occurs at 735, 810 and 851 °C for the pure glass. In the presence of alumina, gahnite emerges first at 700 °C followed by ZnB₂O₄ phase. With mullite as filler, initially ZnB₂O₄ and willemite formed at 700 °C and gahnite phase emerged only at 750 °C and peaks at 787 °C. In the presence of fused silica only ZnB₂O₄ and willemite phases were observed. The dielectric properties of the pure glass and that of the glass + fillers are also reported. Re-crystallization of various low K phases ensures good dielectric porpertis with reduced glass content after sintenring.     

Preparation and characterization of high T c (1−x) BiScO3−xPbTiO3 ceramics from high energy ball milling process

(1-x)BiScO₃?xPbTiO₃ powders were synthesized from a mixture of the oxides Bi₂O₃, Sc₂O₃, PbO and TiO₂ using a Fritsch P4? vario-planetary ball milling systems. The pure perovskite structure of BS-PT powder can well be obtained and the crystallite size of the powders was greatly reduced to 18–25 nm after milling 4 h. The rhombohedral–tetragonal phase boundary was observed for the ceramics sintered at 1,000–1,100 °C when x was around 0.64 and 3–7 μm grain size was obtained, which is smaller than traditional method. High Curie temperature (T _c) and high dielectric constant can be obtained at the morphotropic phase boundary (MPB). As PbTiO₃ contents increased from 60 to 68 mol%, the Curie temperature T _c shifted toward higher temperature and the maximum dielectric constant increased. The experimental results demonstrate that the high-energy ball milling process is a promising method to prepare BS-PT materials.     

Effects of dysprosium oxide addition in bismuth sodium titanate ceramics

This research focuses on the preparation and characterization of dysprosium-doped bismuth sodium titanate (BNT) ceramics. The compounds were prepared using the conventional mixed-oxide method. The amount of dysprosium oxide used was varied from 0 to 2 at.%. The mixed powders were calcined at 800 °C and checked for phase purity using X-ray diffraction technique. The powders were then cold-pressed into small pellets which were subsequently sintered at 1050 °C for 2 h. The results from density measurement and SEM micrographs showed that highly dense and high-purity ceramics were obtained. The grain size of Dy-doped samples was found to decrease with increasing Dy content. Compared to pure BNT, the addition of Dy₂O₃ in BNT ceramics slightly increased the dielectric constant values near room temperature. In addition, the Dy doping resulted in a more diffused transition temperature, less frequency dependence of the dielectric constant and very low values of the dielectric loss.     

Electrical and structural characterization of PTCR pure BaTiO3 nanopowders synthesized by sol–gel emulsion technique

BaTiO₃ ceramics have been widely studied for its application as multilayer ceramic capacitors. However, they have been reported to deviate from their insulating to semiconducting behavior upon doping, and are used as positive temperature coefficient (PTC) thermistors and transducers. In this work, sol–gel emulsion technique was used for synthesis of BaTiO₃ powders of various shapes and sizes. The synthesized powders were calcined at two different temperatures i.e. 750°C, and 1000°C. XRD revealed the powders to be primarily cubic in structure. Presence of tetragonality was noted in the powders calcined at 1000°C. Crystallite size was calculated for the powders calcined at 750°C and 1000°C. Average particle size of the prepared powders varied from 42 to 94?nm. The shape and size of the particles were dependent on the type and concentration of the surfactant used. The synthesized material showed positive temperature coefficient of resistivity (PTCR) behavior. From the recorded resistivity values a maximum of 10¹⁰ Ωcm was achieved. The ferroelectric to paraelectric transition temperature, Curie point, (T_c) was found to be at 75°C from the impedance spectroscopy analysis for the prepared material.     

Microwave-Hydrothermal Synthesis of Ni0.53Cu0.12Zn0.35Fe2O4/SiO2 Nanocomposites for MLCI

The nanocomposites of NiCuZnFe₂O₄-SiO₂ were prepared using Microwave-Hydrothermal method at 160°C/45 min.The as-synthesized powders were characterized using X-ray diffraction and Transmission Electron Microscope (TEM).The average particle size of the powders were found to be ～20 nm.The powders were densified at 900°C/30 min using Microwave sintering method. The sintered composite samples were characterized using XRD and Scanning Electron Microscopy (SEM). Crystallite size of the ferrites decreases with an increase of SiO₂ content. The density of the composites varies of 93–98% of theoretical density. The densities of the present composites were increasing with the addition of SiO_2. The bulk densities of the present composites were increasing with the addition of SiO₂. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer (FTIR) in the 400–4000 cm^?1. The bands in the range of 580–880 cm^?1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe₂O₄ clusters and silica matrix. The resistivity of the sintered samples was increased with an addition of ferrite content. The real and imaginary parts of permittivity and permeability were measured in the frequency range of 1 MHz–1.8 GHz.The addition of SiO₂ alters the values of dielectric constant and permeability which is useful to the Multilayer Chip Inductors (MLCI) fabrication.     

Effect of the firing temperatures on the phase formation,microstructure and electrical properties of BaTi0.91 Sn0.09O3 ceramics synthesized via the solid state combustion method

Abstract

BaTi_0.91Sn_0.09O₃ (BTS) ceramics were synthesized by the solid state combustion method with glycine as the reducting agent and metal nitrates as the oxidants. The calcination and sintering temperatures were in the range of 1200?°C–1300?°C and 1300?°C–1450?°C, respectively, for 2?h. Pure perovskite powders were obtained from the samples calcined at ≥1275?°C for 2?h. The crystal size calculated by Scherrer equation was in the range of 22–30?nm. XRD results of the sintered ceramics showed the coexistence of the tetragonal (T) and orthorhombic (O) phases in all samples, and were confirmed by Rietveld refinement. The grain sizes increased from 9.04 to 29.83 µm when the sintering temperatures increased from 1300?°C–1450?°C for 2?h. The highest density (5.95?g?cm^?3), large piezoelectric strain (d₃₃* = 830?pm/V) and best dielectric constant (ε_r = 14841) were obtained from the sample sintered at 1350?°C for 2?h. This study clearly demonstrates the potential of the solid state combustion method for producing high density and good dielectric properties in BTS ceramics.     

Effect of attrition milling on the piezoelectric properties of Bi0.5Na0.5TiO3-based ceramics

Bismith sodium titanate (BNT)-based powders were prepared by conventionally mixed-oxide method using Bi₂O₃, Na₂CO₃ and TiO₂. The La₂O₃ was added as the modifier to the BNT composition for easily poling and reducing an abnormal dielectric loss at high temperatures. In this study, the investigated compositions were Bi_0.5Na_0.5TiO₃ and Bi_0.5Na_0.485La_0.005TiO₃. The powders were calcined at 900 °C for 2 h by slow heating rate at 100 °C/h. The calcined BNT-based powders were then attrition-milled for 3 h with a high speed at 350 rpm. After drying, the fine powders were uniaxially pressed and then cold-isostatically pressed (CIP) at 240 MPa for 10 min. All pressed pellets were sintered at 1000–1100 °C for 2 h in air atmosphere. The microstructure of sintered pellets was investigated by SEM. Results of dielectric and piezoelectric property measurement were also reported.     

Yttrium iron garnet ceramic prepared from microwave-induced combustion

Yttrium iron garnet (YIG) nano-powders were successfully synthesized by microwave-induced combustion process. The as-prepared YIG powders were annealed at different temperature and investigated by XRD, SEM, and VSM. The as-received YIG powder shows the formation of garnet structure with saturation magnetization (M _s) of 12 emu/g, whereas upon annealing at 825 °C for 2 h, the saturation magnetization increases to 27 emu/g. The as-received yttrium iron garnet powders annealed at several temperatures revealed that the particle size ranged from 65 to 90 nm. Moreover, the linewidth of magnetic resonance peak (ΔH), complex permeability, and loss tangent of sintered YIG ceramic are also examined in this study.