Narrow Results

The effect of a small amount of Sb doping (5%) on the formation of the high temperature superconducting phase has been investigated on the Bi_1.5Pb_0.5Sr₂Ca₂Cu₃O_y compound. It is observed that at 860°C the T_c zero value depends on the sintering time. It first increases to a maximum value of 96 K and then decreases to a stable lowest value of 88 K. The samples have been characterized by X-ray diffraction (XRD), four probe electrical resistance and current density measurements. The XRD revealed the presence of two phases: an orthorhombic high-T_c 2223 phases with lattice constants a = 5.395 Å, b = 5.508 Å, c = 37.0422 Å and another tetragonal low-T_c 2212 phase with lattice constants a = b = 5.419 Å, c = 30.832 Å.

Nanoparticles of samarium barium antimonate (Ba₂SmSbO₆), a complex perovskite has been synthesized using an auto-ignition combustion process for the first time. The nanoparticles thus obtained have been characterized using X-ray diffraction, thermo-gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared powder is phase pure Ba₂SmSbO₆ and has a complex cubic perovskite (A₂BB'O₆) crystalline structure with lattice constant a = 8.491 Å. The particle size of the as-prepared powder was in the range 20–50 nm. The nano crystals of Ba₂SmSbO₆ synthesized by the combustion technique could be sintered to 97% of the theoretical density by heating at a temperature of 1550°C for 2 h. By the present combustion synthesis a phase pure Ba₂SmSbO₆ nanopowder could be obtained by a single step process without the need of any calcination step.

Here we report the investigations on Sm-substituted PZTFN (Pb_1-xSm_xZr_0.588Ti_0.392Fe_0.01Nb_0.01O₃) (where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) polycrystalline solid solutions fabricated by solid-state reaction method. XRD analysis shows all the samples to be single phase with tetragonal structure. Dielectric measurements were carried out in the temperature range 30°C–400°C at different frequencies in the range 100 Hz to 100 kHz. From the temperature variation of dielectric constant (ε), Curie temperature (T_C) was determined which was found to decrease with increasing x. The room temperature dielectric constant (ε_RT) initially increases with increasing x and then starts decreasing. Dielectric loss improves with Sm-doping.

This study aims to fabricate and characterize a series of new complex-structured ceramics with formula (1 - x)Pb(Zr_0.52Ti_0.48)O_3-xBi_3.25Dy_0.75Ti₃O₁₂ or (1 - x)PZT-xBDT (when x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) using a solid state mixed oxide and sintering method. Optimum sintering temperature for this system was found to be 1000°C for 4 h dwell time. Phase analysis using X-ray diffraction indicated existence of BDT- as well as PZT-based solid solutions with corresponding lattice distortion. Scanning electron micrographs of ceramic surfaces showed plate-like structure in BDT-rich phase while typical grain structure was observed for PZT-rich phase. PZT-rich ceramics also possessed high densities due to their more equiaxed grains with high packing capability compared to the ceramics with addition of plate-shaped BDT.

We have examined superconducting property of MgB₂, containing Type 1 elemental superconductor, Pb. The results showed double transition temperatures of superconductivity. Although the addition of Pb considerably improved grain connectivity of MgB₂, the presence of Type I superconducting phase (Pb) degraded the superconductivity of composites by flux creep.

CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by the solid-state reaction route. Effect of sintering time was studied on the polarization (P) versus electric field (E) behavior. Unlike conventional ferroelectric hysteresis loop, PE hysteresis behavior in CCTO ceramics was observed to exhibit ferroelectric-like loop where polarization does not saturate but gives a maximum value. Remnant polarization and maximum polarization was observed to increase with sintering time. Current (I)–voltage (V) characteristics shows a nonlinear behavior making them useful for varistor applications. Coefficient of non-linearity (α) is also found to depend on sintering duration.

A gel was formed when an aqueous solution of BaCl₂, NbF₅ and citric acid in stoichiometric ratio is heated on a water bath at 100°C. This gel on decomposition at 700°C yielded the nano phase of BaNb₂O₆ as confirmed by X-ray diffraction study. The crystal structure is orthorhombic with unit cell parameter a = 12.2136 Å, b = 10.2413 Å, c = 7.8831 Å. The estimated grain size is 88 nm. Dielectric studies reveal the dielectric relaxation mechanism. Conducting charges and free charges both contribute to the dielectric relaxation in this material. Electrical properties of the material were studied using impedance spectroscopy technique. Detailed analysis of impedance spectrum suggested that the electrical properties are strongly temperature-dependent. The relaxation is polydispersive and conduction is mainly through grains. AC conduction activation energies are estimated from Arrheneus plots and conduction mechanism is discussed.

Lead zirconate titanate (PZT) is one of the most important piezoelectric materials widely used for underwater sensors. However, PZTs are hard and non-compliant and hence there is an overwhelming attention devoted toward making it flexible by preparing films on flexible substrates by different routes. In this work, the electrochemical deposition of composition controlled PZT films over flexible stainless steel (SS) foil substrates using non-aqueous electrolyte dimethyl sulphoxide (DMSO) was carried out. Effects of various key parameters involved in electrochemical deposition process such as current density and time of deposition were studied. It was found that a current density of 25 mA/cm² for 5 min gave a good film. The morphology and topography evaluation of the films was carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively, which showed a uniform morphology with a surface roughness of 2 nm. The PZT phase formation was studied using X-ray diffraction (XRD) and corroborated with Raman spectroscopic studies. The dielectric constant, dielectric loss, hysteresis and I–V characteristics of the film was evaluated.

In this study, ZnO nanoparticles and MnO-doped SnO₂-based thick film varistors (TFVs) were fabricated using screen printing technique. The sintering temperature had significant impact on the SZM-based TFVs, especially in terms of grain growth, even at a low sintering temperature of 1100${}^{\circ }$C. The strong solid-state reaction during sintering may be attributed to the large surface area of the 20 nm ZnO nanoparticles that promoted strong surface reaction even at low sintering temperatures. Moreover, the X-ray diffraction lattice constant and full wave at half maximum data indicated that the sintering process also improved the grain crystallinity with the decrease in intrinsic compressive stress. The sintering temperatures also significantly influenced the electrical properties of the SZM-based TFVs with a significant decrease in the breakdown field from 360 V/mm (sample at 1100${}^{\circ }$C) to 158 V/mm (sample at 1250${}^{\circ }$C). The grain boundary resistance ($R_{\mathrm{\text{GB}}})$ also experienced a dramatic drop from 266.4 k$\mathrm{\Omega }$ (sample at 1100${}^{\circ }$C) to 89.46 k$\mathrm{\Omega }$ (sample at 1250${}^{\circ }$C). The sample sintered at 1200${}^{\circ }$C exhibited superior electrical behaviors with a nonlinear exponent of 61 and leakage current of 115 $\mu$A. Furthermore, it achieved high permittivity and low dissipation factor at the low frequency range. The conduction behaviors of ${\mathrm{\text{O}}}^{\prime }$ ions with activation energy of approximately 0.6 eV was dominated by decreasing ${\mathrm{\text{Zn}}}_{\mathrm{\text{Sn}}}^{\prime \prime }$ and ${\mathrm{\text{Mn}}}_{\mathrm{\text{Sn}}}^{\prime \prime }$ defects (around 0.4 eV) with increasing sintering temperature. Therefore, the sintering process can be applied to control the conduction behaviors of SZM-based TFVs doped with ZnO nanoparticle powder and achieve improved structural and electrical properties with good nonlinear behaviors.

This paper investigates the effects of interparticle distance and heating rate on the aggregation characteristics of Cu/Au nanoparticles using molecular dynamics (MD) simulations, and focuses on discussing the effects of the two above-mentioned factors on the entire system. Our results suggested that the reduction in heating rate and increasing the initial distance of the particles would both contribute to raising the initial sintering temperature. However, when the particles’ initial distance was greater than the cut-off radius of the system, the initial sintering temperature was not increased any longer, but fluctuated within a certain range. Furthermore, the sintering force of the nanoparticles at the initial sintering temperature was investigated, and it was found that the heating rate made no obvious difference to it. Nonetheless, the sintering force varied under different initial distance of the particles (at the same heating rate) due to system energy changes.

The materials’ consolidation, especially ceramics, is very important in advanced research development and industrial technologies. Science of sintering with all incoming novelties is the base of all these processes. A very important question in all of this is how to get the more precise structure parameters within the morphology of different ceramic materials. In that sense, the advanced procedure in collecting precise data in submicro-processes is also in direction of advanced miniaturization. Our research, based on different electrophysical parameters, like relative capacitance, breakdown voltage, and $\mathrm{\text{tg}}\delta$, has been used in neural networks and graph theory successful applications. We extended furthermore our neural network back propagation (BP) on sintering parameters’ data. Prognosed mapping we can succeed if we use the coefficients, implemented by the training procedure. In this paper, we continue to apply the novelty from the previous research, where the error is calculated as a difference between the designed and actual network output. So, the weight coefficients contribute in error generation. We used the experimental data of sintered materials’ density, measured and calculated in the bulk, and developed possibility to calculate the materials’ density inside of consolidated structures. The BP procedure here is like a tool to come down between the layers, with much more precise materials’ density, in the points on morphology, which are interesting for different microstructure developments and applications. We practically replaced the errors’ network by density values, from ceramic consolidation. Our neural networks’ application novelty is successfully applied within the experimental ceramic material density $\rho =5.4\times 10^3$ [kg/m³], confirming the direction way to implement this procedure in other density cases. There are many different mathematical tools or tools from the field of artificial intelligence that can be used in such or similar applications. We choose to use artificial neural networks because of their simplicity and their self-improvement process, through BP error control. All of this contributes to the great improvement in the whole research and science of sintering technology, which is important for collecting more efficient and faster results.

Zinc silicate was successfully synthesized by solid-state sintering at the temperature no less than $1100^{\circ }$C. Co-existing ZnO phase was observed as adopting the stoichiometry reactant ratio 2:1 of ZnO:SiO₂. Single-phase $\alpha$-Zn₂SiO₄ (willemite structure) was obtained by adjusting the ZnO:SiO₂ ratio to 1:1. Prolonging sintering time has helped to increase the fluorescence efficiency and what is more, repeated solid-state sintering process is found to have further improved fluorescence of Zn₂SiO₄:Mn.

BaTiO₃ (BTO) is considered the most commonly used ceramic material in multilayer ceramic capacitors due to its desirable dielectric properties. Considering that the miniaturization of electronic devices represents an expanding field of research, modification of BTO has been performed to increase dielectric constant and DC bias characteristic/sensitivity. This research presents the effect of N₂ and air atmospheres on morphological and dielectric properties of BTO nanoparticles modified with organometallic salt at sintering temperatures of $1200^{\circ }$C, $1250^{\circ }$C, $1300^{\circ }$C, and $1350^{\circ }$C. Measured dielectric constants were up to 35,000, with achieved very high values in both atmospheres. Field emission scanning electron microscopy (FESEM) was used for morphological characterization, revealing a porous structure in all the samples. The software image analysis of FESEM images showed a connection between particle and pore size distribution, as well as porosity. Based on the data from the image analysis, the prediction of dielectric properties in relation to morphology indicated that yttrium-based organometallic salt reduced oxygen vacancy generation in N₂ atmosphere. DC bias sensitivity measurements showed that samples with higher dielectric constant had more pronounced sensitivity to voltage change, but most of the samples were stable up to 100 V, making our modified BTO a promising candidate for capacitors.

In this paper, alumina-reinforced copper-based composite materials were prepared by using the electroless plating method to coat copper powder with a layer of silver and then combining the solution sol method and powder metallurgy method. The results show that recrystallized structures and twins appear in composite materials after high-temperature sintering. As the sintering temperature increases, the ratio of recrystallized structures and twins gradually decreases, and straight coherent $\mathrm{\Sigma }$3 annealing twins appear in the structure, the number of high-angle grain boundaries decreased, the number of small-angle grain boundaries continues to increase, the average grain size increased from 3.89 to 4.83$\mu$m, the tensile strength increased from 156MPa to 167.5MPa, the maximum elongation was 9.4%, and the density increased from 6.81g/cm³ increased to 7.62g/cm³, the porosity dropped from 13.3% to 5.5%, the conductivity increased from 60.3% IACS to 73.2% IACS, the maximum hardness value was 68.71 HV, the best performance of the composite was achieved by sintering at 900°C with the tensile strength and elongation are 163MPa and 9%, respectively, the conductivity is 68.9% IACS, and the density is 7.35g/cm³. Its fracture surface shows mostly ductile features.

The main purpose of this work is to optimize the mechanical properties of tungsten–copper (W–Cu) nanocomposite fabricated by the sintering process. For this purpose, the parameters of sintering temperature, sintering time and weight percentage of copper were selected to optimize the compression strength, impact strength, hardness and corrosion resistance of the W–Cu nanocomposite using the desirability function procedure and response surface method. The analyses of transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were also performed to examine the microstructure of W–Cu nanocomposite. The results exhibited that a rise in the sintering temperature from 1000^∘C to 1150^∘C significantly enhanced the impact strength of W–Cu nanocomposite, while a rise in the sintering temperature from 1150^∘C to 1300^∘C deteriorated the impact strength. Moreover, the compression strength and hardness of the W–Cu nanocomposite continuously improved by elevation of sintering temperature from 1000^∘C to 1300^∘C. A rise in the amount of Cu from 20wt.% to 40wt.% led to a reduction in the hardness of the W–Cu nanocomposite, while a rise of Cu content improved the impact and compression strengths. The results also indicated that the mechanical properties of W–Cu nanocomposite enhanced simultaneously by using 27wt.% Cu at sintering temperature of 1197^∘C and sintering time of 2.7h. The samples sintered at the optimal conditions indicated a higher corrosion resistance than that sintered at the initial conditions.