Microwave dielectric properties of barium substituted screen printed CaBi2Nb2O9 ceramic thick films

In the present study, Aurivillius-structured Ba²⁺ substituted CaBi₂Nb₂O₉ (CBNO) ceramic powder was synthesized by co-precipitation method. The CBNO thick films were delineated by screen printing method on alumina substrates using co-precipitated ceramic powder. The overlay method was adopted to measure the microwave dielectric properties of prepared thick films. Single phase layered perovskite structure of the prepared thick films was confirmed by X-ray Diffraction. The effects of Ba²⁺ substitution on the surface morphology, bonding, and microwave dielectric properties of thick films were systematically presented. The maximum value of microwave dielectric constant for the CBNO thick films at 11.8 GHz is 15.6 for Ba²⁺=0.8 substitution. The shift in the stretching vibration modes of the Nb-O bond of NbO₆ octahedron in the Raman spectra with a substitution of Ba²⁺ in CBNO was observed. The substitution of Ba²⁺ on A-site of CBNO improves the microwave dielectric properties of prepared thick films. This work may provide a new approach to enhance the microwave dielectric performance of Aurivillius-structured ceramic thick films.     

High performance PZT thick film actuators using in plane polarisation

Piezoceramic thick films offer the possibility of integrated functional components in planar design. They can be applied as sensors, actuators, ultrasonic transducers, transformers and generators. Typically, piezoceramic thick films are excited through the film thickness. In contrast, in-plane mode of excitation will be beneficial especially for actuator applications. The use of interdigitated electrodes (IDEs) enables in-plane excitation of piezoceramic thick films. Actuator performance of cantilever structures with through thickness and in-plane polarised piezoceramic thick films are investigated. The performance of in-plane polarised cantilevers depends on the particular IDE spacing. Using finite element simulations of the E-field distribution, geometrical and design efficiencies are considered and compared to experimentally derived data.     

Sintering and electrical properties of Cu-substituted Zn-Co-Ni-Mn spinel ceramics for NTC thermistors thick films

We report on the preparation, sintering and electrical properties of new Cu-substituted spinels Zn_0.5Ni0.4Co_0.4Mn_1.7-xCu_xO₄ and Zn_0,5Ni_0,5Co_0,5Mn_1,5-xCu_xO₄ (0.1 ≤ x ≤ 0.4) for thick film NTC thermistors. Bulk samples were sintered at 900 °C and Cu-rich spinels achieve high density. The thermal stability is limited by the decomposition temperature T_d. However, a T_d ≥ 900 °C for x = 0.4 allows firing of bulk samples and films at 900 °C. The room temperature resistivity and thermistor B-values decrease with x. NTC thermistor thick films were fabricated by screen-printing of spinel pastes (x = 0.4) onto alumina substrates and firing at 900 °C. Addition of BBSZ glass to the thermistor paste allows for sintering of the films at 850 °C. The NTC thermistor films exhibit excellent thermistor performance with R_□25°C = (652 ± 5) kΩ/sq, B = (3342 ± 17) K, and good ageing stability (< 2% after 600 h at 150 °C).     

Low-temperature sintering and electrical properties of Ba0.68Sr0.32TiO3 thick films

Ba_0.68Sr_0.32TiO₃ (BST) thick films were prepared by screen printing on a flexible fluorophlogopite substrate. In order to realise the co-firing of the BST film with a silver electrode at a lower temperature, the BST precursor was used as a solvent for the screen-printing slurry and the cold sintering technique was used to pretreat the film. The sintering temperature of BST thick films prepared by conventional sintering process was higher than 1200 °C. When sintered at 950 °C, the thick films exhibited a high porosity. The density of the thick films was significantly improved after pretreatment with the cold sintering process (CSP). After the cold-sintered thick films were sintered at 950 °C for 30 min and then fired with a silver electrode, the samples exhibited a relative dielectric constant of 773 (at 25 °C and 10 kHz), a dielectric loss of 0.025, a remanent polarization of 5.3 μC/cm², and a coercive field strength of 38.1 kV/cm. Therefore, the low-temperature co-firing of BST thick films with a silver electrode was successfully realised.     

Sintering behavior,microstructure and thermoelectric properties of calcium cobaltite thick films for transversal thermoelectric multilayer generators

The sintering behavior and the thermoelectric performance of Ca₃Co₄O₉ multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920 °C, whereas dense and isotropic multilayer samples were prepared by firing at 1200 °C and reoxidation at 900 °C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920 °C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A transversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca₃Co₄O₉ green tapes, AgPd conductor printing, and co-firing at 920 °C. The TMLTEG has a power output of 3 mW at ΔT = 200 K in the temperature interval of 25 °C to 300 °C.     

Microstructural,structural, dielectric and piezoelectric properties of potassium sodium niobate thick films

In the framework of a systematic study, we present the influence of processing parameters – in particular the presence of a packing powder during sintering and the sintering temperature – on the microstructural and structural properties of potassium sodium niobate (K_0.5Na_0.5NbO₃ or KNN) thick films. These KNN thick films were prepared with a 1 mass% addition of potassium sodium germanate (KNG), which serves as a liquid-phase sintering aid. The sintered films exhibited preferential crystallographic orientations along [100]_pc and [10−1]_pc, the origin of which lies in the compressive stresses developed during cooling as a result of the thermal expansion mismatch between the film and the substrate. In addition, the dielectric permittivity, dielectric losses and the piezoelectric d₃₃ coefficient of the obtained films were compared with those of KNN bulk ceramics.     

Spectroscopic and photoluminescence characteristics of Sm3+ doped calcium aluminozincate phosphor for applications in w-LED

Monophase Calcium Aluminozincate (Ca₃Al₄ZnO₁₀) phosphor doped with Sm³⁺ ions by varying concentrations have been prepared at 1300 °C using conventional solid state reaction technique. The crystal structure and phase analysis of the as-prepared phosphor has been carried out by X-ray Diffraction (XRD) studies. Morphology and functional groups present in the phosphor have been investigated thoroughly by using Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FT-IR) spectral measurements, respectively. Under 401 nm excitation, the as-prepared phosphor exhibit intense visible orange emission at 601 nm. It has been observed that 1.0 mol% of Sm³⁺ ions concentration is optimum to give intense visible orange emission. The PL analysis reveals that the dipole-dipole interaction is primarily responsible for the concentration quenching observed beyond 1.0 mol% of Sm³⁺ ions. The TR-PL study reveals a bi-exponential behavior of decay curves with an average lifetime of the order of microseconds. The CIE coordinates (x=0.574 and y=0.424) measured for the optimized phosphor are very close to the intense orange emission coordinates specified by Nichia Corporation developed Amber LED NSPAR 70BS (0.570, 0.420). The spectroscopic, PL and TR-PL studies suggest the potential use of Sm³⁺ doped calcium aluminozincate phosphors for display and white light emitting devices.     

Synthesis,characterization and enhanced acetone sensing performance of Pd loaded Sm doped SnO2 nanoparticles

In the present communication, we have presented a high performance acetone sensor based on Pd loaded Sm doped SnO₂ nanomaterial. The (0.5, 1, 2 and 3) wt% Pd loaded 6 mol% Sm doped SnO₂ nanoparticles were prepared using a co-precipitation method. The characterization of samples was done by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FEG-SEM), Energy Dispersive Analysis by X-rays (EDAX), High Resolution-Transmission Electron Microscopy (HR-TEM) and Selective Area Electron Diffraction (SAED) techniques. The gas response studies such as sensitivity, selectivity and stability towards liquid petroleum gas, ammonia, ethanol and acetone were measured at 100 ppm concentrations. The results show that optimum Pd loading (2 wt%) results in smaller crystallite size (~3.1 nm), lower operating temperature (200 °C), higher gas response (94%),better selectivity, faster response (~3 s) and quicker recovery (~12 s) towards acetone.     

Synthesis, characterization and electrochemical properties of copper phosphide (Cu3P) thick films prepared by solid-state reaction at low temperature: a probable anode for lithium ion batteries

Copper phosphide (Cu₃P) was produced as thick films over copper foils. The synthesis was performed by solid-state reaction at low temperature (400 °C). Similar attempts were carried out for other transition metals of the first series without success. Scanning electron microscopy (SEM) revealed the formation mechanism of the Cu₃P thick films. First, phosphorus diffuses into the copper foil followed by the subsequent formation of the binary compound. During this process, the Cu₃P particles seem to dig the copper foil, producing holes, where the Cu₃P crystallites nucleate and growth. Then, the thick films are formed by the conjugation of several agglomerates and their morphology is not homogeneous. Oxidation of Cu₃P occurs to a small extend on the top surface of the films. The electrochemical behaviour of the thick film was compared with a standard Cu₃P composite electrode, in which the active material is mixed with carbon and a binder. Although the two different electrodes presented some differences in their electrochemical behaviour, both electrodes showed promising qualities to be used as anode materials in lithium ion batteries or hybrid devices.     

Ternary doping of Na+, Bi3+ and La3+ to improve piezoelectric constant and electrical resistivity simultaneously in calcium bismuth niobate ceramics

High Curie-temperature layer-structured calcium bismuth niobate (CaBi₂Nb₂O₉) piezoelectric ceramics are promising for important application in high-temperature vibration sensors. However, such application is currently limited due to not only poor high-temperature piezoelectric constant (d₃₃), which is attributable to spontaneous polarization along a-b plane and high coercive fields, but also inferior high-temperature electrical resistivity, which results from volatilization of Bi₂O₃ during the sintering process that increases defect concentration of oxygen vacancies. Herein, we report a Na⁺, Bi³⁺ and La³⁺ ternary-doping-strategy to obtain Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics, which exhibited higher piezoelectric constant and larger electrical resistivity as accompanied by a better thermal stability at high-temperatures. The piezoelectric constant was enhanced from 8.8 pC/N in pristine CaBi₂Nb₂O₉ to 13.4 pC/N in Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics, which is ascribed to the presence of pseudo-tetragonal structural distortion after La³⁺ doping. In addition, the electrical resistivity at 600 °C was increased by more than one-order of magnitude from 3.7 × 10⁴ Ω cm in pristine CaBi₂Nb₂O₉ to 1.4 × 10⁶ Ω cm in Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics. Such significant improvement in electrical resistivity results from the reduction in oxygen vacancies due to ternary doping of Na⁺, Bi³⁺ and La³⁺ and stronger binding interaction between La³⁺ dopants and O^2? in (Bi₂O₂)²⁺ layers in Ca_0.8(Na_0.5La_0.3Bi_0.2)_0.2Bi₂Nb₂O₉ ceramics. This work demonstrates an important way of employing chemical doping to improve piezoelectric constant and electrical resistivity simultaneously at high-temperatures to tune structural distortion in bismuth-layered structural CaBi₂Nb₂O₉ ceramics.     

Enhancement of energy storage and thermal stability of relaxor Pb0.92La0.08Zr0.52Ti0.48O3-Bi(Zn0.66Nb0.33)O3 thick films through aerosol deposition

Relaxor ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT 8/52/48) has been studied widely for applications to high energy storage capacitors because of its polarization-electric (P-E) field hysteresis. On the other hand, its energy storage characteristics are unsatisfactory because the dielectric properties deteriorate with temperature. In the present study, a dense nano-composite thick film (∼5 μm) was fabricated by the aerosol deposition (AD) of mixed powders of BZN [Bi(Zn_0.66Nb_0.33)O₃] corresponding to 0, 5, and 10 at.% with lanthanum-doped lead zirconate titanate ceramics (PLZT) at room temperature, followed by post-annealing for crystallization recovery. The composition of 0.95(Pb_0.92La_0.08Zr_0.52Ti_0.48O₃)-0.05Bi(Zn_0.66Nb_0.33O₃) PLZT-BZN5 was made artificially, which accommodates the coexistence of two different phases, demonstrating superior energy storage performance. The 550°C-annealed PLZT-BZN5 film showed a superior energy density of 14.7 J/cm³ under an electric field of 1400 kV/cm and an efficiency of 81%. The PLZT-BZN5 film also exhibited low dielectric loss and improved temperature stability.     

Effect of Ag+ doping and Ag addition on the thermoelectric properties of KSr2Nb5O15

The electron and phonon thermal transport behavior of Ag ⁺ doped KSr₂Nb₅O₁₅ were discussed by using the first-principles calculations. The band gap was reduced after Ag⁺ doping, and the electrons near the Fermi level had stronger transition capability, which effectively increased the carrier concentration and electrical conductivity and reduced the thermal conductivity, thereby improving the ZT of the doped KSr₂Nb₅O₁₅ from 0.6298 to 0.7214 (1200 K) under ideal conditions. In addition, the solid-state reaction method was used to prepare Ag nanoparticle added KSr₂Nb₅O₁₅ samples, and their thermoelectric performance was tested. The experimental results and the calculated results showed a good consistent trend in which Ag improved the thermoelectric properties of KSr₂Nb₅O₁₅. When the amount of addition of nanosized Ag was 20 wt%, the power factor and ZT of the material were the highest at 1073 K, which were 0.228 mW/(K²·m) and 0.1090, respectively. This research shows how to improve the thermoelectric performance of KSr₂Nb₅O₁₅ ceramics and broaden their temperature range for application.     

Improved conductivity in tape casted Li-NASICON supported thick films: Effect of temperature treatments and lamination

In this work, the influence of different thermal sintering treatments on Li_1.3Al_0.3Ti_1.7(PO₄)₃ NASICON thick films has been investigated. The isostatic lamination step performed before the thermal sintering of thick films has demonstrated to improve film density and grain size, increasing "bulk" and grain boundary Li-conductivities. The confocal Raman spectroscopy characterization allowed the observation of the connectivity of the particles present in the ceramic samples and so a deeper understanding of ionic conductivity. The dependence of total and "bulk" Li conductivity on the samples microstructure is discussed. The films sintered by slow heating sintering with a previous lamination step, displayed an overall Li- conductivity >10^?4 Ω^-1 cm^-1, that is superior to that reported in commercial OHARA Li- NASICON glass ceramics. The tape casting deposition method is scalable for preparation of large area thick supported electrolyte films with high conductivity for novel Li ion all solid state batteries (ASSB) architectures.     

Effect of substrate on the microstructure and thermoelectric performances of Sr-doped Ca3Co4O9 thick films

Ca₃Co₄O₉ thermoelectric materials in form of thick films are very promising in practical applications due to their low costs and relatively high performance. In this work, two different suspensions have been used to produce different coatings on Al₂O₃ polycrystalline substrates with theoretical green thickness of 360 and 2000?µm. Moreover, the effect of substrate has also been investigated using Al₂O₃ monocrystalline substrates and a 360?µm green thickness. Sintering procedure at 900?°C for 24?h has drastically decreased coating thickness. XRD performed on the coatings surface has shown the formation of small amounts of Ca₃Co₂O₆ secondary phase on the polycrystalline substrates, while it was more abundant, and accompanied by Ca₂Co₂O₅ on the monocrystalline substrates. In spite of the higher secondary phases content, monocrystalline substrates produced a slight grain orientation which led to the highest thermoelectric properties between the samples (0.38?mW/K²m at 800?°C), and very close to the best reported values in the literature.     

Microstructure and micromechanical properties of GaV4S8 ceramics prepared by single-step solid state synthesis

Despite the current focus on the electronic properties of GaV₄S₈ lacunar spinel, the microstructural and mechanical characterization of this material is scarce in the literature. In this work, we propose an effective GaV₄S₈ ceramics production method and provide a detailed microstructural and micromechanical characterization. Light microscopy, scanning electron microscopy and X-ray diffraction are used to describe the microstructure of the ceramic targets that can be used for thin film deposition. V₂O₃ was found to be the main impurity in ceramic targets and its content is discussed with respect to the sintering atmosphere control. Nanoindentation and microcantilever bending were employed to provide estimates of the indentation modulus, hardness and fracture stress of individual grains. The values of these parameters have been determined as E_r = 130 ± 2 GPa, H = 8.9 ± 0.2 GPa and σ_c = 600 ± 57 MPa, respectively.     

Fabrication and characterization of porous mullite ceramics with ultra-low shrinkage and high porosity via sol-gel and solid state reaction methods

Porous mullite ceramics with ultra-low shrinkage and high porosity were prepared by solid state reaction between MoO₃ and mullite precursor powders which were synthesized from tetraethylorthosilicate and aluminium nitrate nonahydrate via sol-gel methods. The synthetic process of mullite precursor powder and effects of MoO₃ amount on the phase composition, microstructure, physical properties such as firing shrinkage, open porosity, bending strength, water absorption and bulk density of porous mullite ceramics were investigated. The results indicated that the addition of MoO₃ not only lowered the mullite forming temperature from 985.4 to 853.3 °C, but also restrained densification behavior of samples due to the formation of mullite and Al₂O₃–MoO₃ solid solution, besides, MoO₃ also improves the formability, open porosity and bending strength of samples. The optimal amounts of MoO₃ is 8 wt%, and the resultant samples exhibit outstanding properties, including a low shrinkage rate of 1.86 ± 0.07%, an open porosity of 61.91 ± 0.16% and a bending strength of 9.35 ± 1.11 MPa.     

Effect of La3+, Ag+ and Bi3+ doping on thermoelectric properties of SrTiO3: First-principles investigation

First principles calculations were applied to study the thermoelectric properties of La³⁺-, Ag⁺- and Bi³⁺- doped SrTiO₃. With the exception of Sr_0.9La_0.1TiO₃, the band gaps of Sr_0.8La_0.1Ag_0.1TiO₃, Sr_0.8La_0.1Bi_0.1TiO₃ and Sr_0.7La_0.1Ag_0.1Bi_0.1TiO₃ were higher than that of SrTiO₃. La³⁺, Ag⁺, and Bi³⁺ doping can cause an increase in electrical conductivity and power factor, and a decrease in thermal conductivity, which improves the ZT. The thermal conductivities of SrTiO₃, Sr_0.9La_0.1TiO₃, Sr_0.8La_0.1Ag_0.1TiO₃, Sr_0.8La_0.1Bi_0.1TiO₃ and Sr_0.7La_0.1Ag_0.1Bi_0.1TiO₃ successively decreased, while power factor and ZT increased. Sr_0.7La_0.1Ag_0.1Bi_0.1TiO₃, in particular, has the smallest thermal conductivity (2.237 W/m/K), the highest power factor (1.18 mW/(mK²)) and ZT (0.597) at 1200 K, 2.195 times larger than that of SrTiO₃ (0.272). In addition, the solid state reaction method was applied to prepare dense ceramics of 10 wt% Bi-doped and (Bi, Ag)-codoped Sr_0.9La_0.1TiO₃. It is demonstrated that (Bi, Ag)-codoped Sr_0.9La_0.1TiO₃ have improved power factors, thermal conductivities and ZT values. The calculations and experimental results are consistent. This work demonstrates a method of co-doping Bi³⁺, Ag⁺, and La³⁺ to enhance the thermoelectric performance of SrTiO₃.     

Phase formation and crystallization kinetics in cordierite ceramics prepared from kaolinite and magnesia

In this work, Algerian kaolinite, a naturally occurring clay mineral, was used as low-cost precursor for the synthesis of cordierite ceramics. The kaolinite was mixed with synthetic magnesia, and the mixture was ball milled and reaction sintered in the temperature range 900–1350 °C for 2 h. Thermogravimetry (TG), differential thermal analysis (DTA), dilatometry, high temperature x-ray powder diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) complementary techniques were used to analyze sintering behavior, characterize phase transformations, and investigate crystallization kinetics. Milling the kaolinite and magnesia mixture for 10 h yielded a homogenous powder, decreased the average particle size, and improved the roundness of particles. Different crystalline phases were present in the samples sintered in the temperature range 900–1150 °C, the cordierite phase started to crystallize at 1200 °C, and the formation of highly dense cordierite (99%) was complete at 1250 °C. The activation energy values for cordierite formation calculated using Kissinger, Boswell, and Ozawa methods were found to be equal to 577, 589, and 573 kJ/mol, respectively. The kinetic parameters n and m had values close to 2. Bulk nucleation with a constant number of nuclei was the dominant mechanism in cordierite crystallization, followed by two-dimensional growth controlled by interface reaction.     

Structural and thermal studies of silver nanoparticles and electrical transport study of their thin films

This work reports the preparation and characterization of silver nanoparticles synthesized through wet chemical solution method and of silver films deposited by dip-coating method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy dispersive spectroscopy (EDX) have been used to characterize the prepared silver nanoparticles and thin film. The morphology and crystal structure of silver nanoparticles have been determined by FESEM, HRTEM, and FETEM. The average grain size of silver nanoparticles is found to be 17.5 nm. The peaks in XRD pattern are in good agreement with that of face-centered-cubic form of metallic silver. TGA/DTA results confirmed the weight loss and the exothermic reaction due to desorption of chemisorbed water. The temperature dependence of resistivity of silver thin film, determined in the temperature range of 100-300 K, exhibit semiconducting behavior of the sample. The sample shows the activated variable range hopping in the localized states near the Fermi level.