Fine-grained Ceramics Research Articles

Effect of preparation methods on structural and dielectric properties of Ba0.985Bi0.01Mn0.067Ti0.933O3 ceramics for multilayer ceramic capacitors

Ba0.985Bi0.01Mn0.067Ti0.933O3 (BBMT) ceramic samples were prepared using solid phase and precipitation methods. The influence of preparation method on phase composition, microstructure, and dielectric properties of BBMT ceramic samples was studied. Results show that grain size of ceramic sample prepared by solid-phase method (BBMT-1) was not uniform and was larger than 1 µm. The dielectric peak at the Curie temperature was sharp and the tangent loss was large (0.067). Fine-grained ceramics (BBMT-2) with uniform grain size (∼300 nm) were prepared by precipitation, and these ceramics exhibited broadened, flattened permittivity peaks. At room temperature, BBMT-2 ceramic samples have high dielectric constant of 1280 and low dielectric loss of 0.028, and samples exhibit good stability at temperatures ranging from −60 to 110 °C. These materials have potential applications in multilayer ceramic capacitors (MLCCs).

Multi-Wire Sawing of Translucent Alumina Ceramics

Multi-wire sawing has emerged as the leading technology in wafer production for a variety of semiconductor materials. This study investigates the process stability and efficiency of conventional semiconductor multi-wire slurry saws in routinely machining translucent, high-density alumina ceramics. The brittle and fine-grained translucent alumina ceramics with extreme hardness and wear resistance represents a major challenge for the process. The alumina ceramic substrates are used for sensor applications, energy storage technology and applications in power electronics. An ideal adaptation of the sawing process parameters to the workpiece properties guarantees the efficiency of the slurry sawing process and the quality of the ceramic wafers. An indicator of the efficiency and cutting ability of the sawing process is the size of the bow of the wire web. The first time was shown that the wire bow can be used for the characterization of the sawing processes for hard and brittle technical ceramics. It was found that a longer workpiece length, a higher number of wafers and stronger abrasive wear lead to an increased size of the bow. The rocking frequency has no measurable influence on the size of the bow. Knowledge of these relations is an extremely valuable tool in the sawing process development for hard and brittle technical ceramics.

Experimental Study of Dynamic Strength of Aluminum Oxide Based Fine-Grained Ceramics Obtained by Spark Plasma Sintering

Experimental Study of Dynamic Strength of Aluminum Oxide Based Fine-Grained Ceramics Obtained by Spark Plasma Sintering

Fabrication and luminescent properties of fine-grained cerium-doped lutetium-yttrium oxyorthosilicate ceramics

When compared to Lu2SiO5:Ce (LSO:Ce), cerium-doped lutetium-yttrium oxyorthosilicate solid solutions not only possess a similar density, but they also exhibit good scintillation properties (high light yield, short decay time and good energy resolution). Fine-grained Lu1.8Y0.2SiO5:Ce (LYSO:Ce) ceramics were fabricated via Spark Plasma Sintering (SPS) at a temperature of 1050 °C and an applied pressure of 100 MPa from a nano-sized LYSO:Ce powder. The average grain size of the sintered LYSO:Ce ceramics is 210 nm. To eliminate the oxygen vacancies that result from the sintering process, the sintered LYSO:Ce ceramics were subsequently annealed at 950 °C for 40 h in air. The in-line transmittance of the LYSO:Ce ceramics is 1.7% at 420 nm. The light yield of the annealed LYSO:Ce ceramics is 23,600 photons/MeV. It is suggested that SPS combined with annealing in air is a promising route to fabricate fine-grained LYSO:Ce ceramics with good scintillation performance.

Influence of sintering temperature on structural and optical properties of Y2O3–MgO composite SPS ceramics

The paper studies infrared-transparent 50:50 vol% Y2O3–MgO fine-grained composite ceramics produced via glycine-nitrate process and spark plasma sintering (SPS). Effect of SPS temperature (T = 1100, 1200, 1250 and 1300 °С) on consolidation processes of Y2O3–MgO nanopowders and on ceramics properties has been investigated. Morphology, structural-phase state, density, Vickers microhardness and infrared transmittance of Y2O3–MgO nanocomposites have been studied. Transmittance has been found to increase with the SPS temperature reaching 71%@6000 nm wavelength at T = 1300 °C. Maximal Vickers hardness of 10.9 GPa has been achieved at T = 1200 °C. The correlation between processing conditions of ceramics and indicated characteristics was investigated.

Microstructural freezing of highly NIR transparent Y2O3-MgO nanocomposite via pressure-assisted two-step sintering

Y2O3-MgO nanocomposite has attracted attention for use in infrared windows and domes. However, the large difference in refractive index between the two phases of this materials phases induces inevitable grain boundary scattering. To overcome this drawback, it is indispensable to greatly reduce the grain size and eliminate residual pores. Two-step sintering has been extensively used to produce fine-grained ceramics, but long incubation time and an additional process are required. As a robust approach, pressure-assisted two-step consolidation of Y2O3-MgO nanocomposite ceramics is investigated to achieve full density while retaining domain size. A sintering path for pressure-assisted two-step sintering and related kinetic window are obtained for the first time. By effectively suppressing grain growth and eliminating residual pores via two-step hot-pressing, outstanding mid- and near-infrared transmittance were achieved. The results indicate that pressure-assisted two-step sintering is a promising alternative strategy that can decrease the domain size and achieve full density of ceramics.

Properties of Ceramics Obtained Based on Mechanically Mixed Powders of Zirconium Hydroxide and a Dopant

The results of studies of the structure, phase composition and specific surface area of powders based on zirconium dioxide obtained by the method of thermal decomposition of a mechanical mixture of hydroxide and a stabilizing additive are presented. The forming and sintering of ceramic samples obtained from calcined powders were studied, as well as some properties of the ceramics. It has been shown that fine-grained dense high-strength ceramics with a flexural strength of 860 MPa and microhardness up to 12 – 13 GPa can be obtained from the synthesized powders.

Fine-grained BNT-based lead-free composite ceramics with high energy-storage density

The low breakdown strength of BNT-based dielectric ceramics limits the increase in energy-storage density. In this study, we successfully reduced the sintering temperature of BNT-ST-5AN relaxor ferroelectric ceramics from 1150 to 980 °C by two-phase compounding with nano-SiO2. Meanwhile, the average grain size of the composite ceramics is also greatly reduced from 4.45 μm to 0.37 μm. Thus, a large recoverable energy-storage density (3.22 J/cm3) is achieved under the ultrahigh breakdown strength (316 kV/cm). Moreover, good temperature (25–150 °C) and frequency (10–200 Hz) stabilities are simultaneously achieved. The excellent energy-storage properties suggest that BNT-ST-based ceramics composited with SiO2 form a promising low-temperature sintered dielectric material for pulsed power multilayer ceramic capacitors.

Large energy density with excellent stability in fine-grained (Bi0.5Na0.5)TiO3-based lead-free ceramics

In this work, fine-grained (0.95-x)(Bi0.5Na0.5)TiO3-0.05BaTiO3-xBi(Zn2/3Nb1/3)O3 (abbreviated as BNT-BT-xBZN, x = 0∼0.20) lead-free ceramics are successfully prepared, showing a high energy storage performance. The addition of BZN results in decreased grain size, enhanced breakdown strength and stronger relaxor behavior with polar nanoregions. Slimmer P-E loops are thereby achieved, leading to the improvement of energy density and efficiency. As a result, a high WD of ∼2.83 J/cm3 is achieved under a relatively low electric field of 18 kV/mm in the x = 0.125 ceramic with submicron-sized grains (∼0.4 μm). The WD value is larger than that of x = 0 ceramic by ∼800%. Furthermore, the x = 0.125 ceramic possesses excellent frequency stability and strong fatigue endurance. The BNT-BT-xBZN lead-free ceramics show promising potential for application in high energy density ceramic capacitors.

Correlation of Al2O3-Ceramic Structure with the Mechanism of Surface Layer Formation for Workpieces During Diamond Grinding

Correlation of the structure of Al2O3 ceramics with specimen polished surface roughness and morphology is established. On basis of this the physical nature of surface layer formation during diamond grinding of fine-grained and coarse-grained ceramics is been revealed.

Overcoming the abnormal grain growth in Ga-doped Li7La3Zr2O12 to enhance the electrochemical stability against Li metal

Abstract Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolyte is a promising candidate for next generation batteries. In the LLZO family with various doping elements, Ga-doped LLZO (Ga-LLZO) delivers the highest Li-ion conductivity of higher than 1 × 10 −3 S cm −1 . However, Ga-LLZO ceramics always contain lots of overgrown huge grains after sintering, resulting in short-circuiting as applied with Li anode in batteries. Hence a simple two-step sintering strategy is developed to prepare fine-grained Ga-LLZO ceramics with good electrochemical properties. Pellets with the composition of Li 6.4 Ga 0.2 La 3 Zr 2 O 12 deliver pure garnet phase, uniform fine grains, high relative density of 97.3% and conductivity of 1.24 × 10 −3 S cm −1 at 27 °C after sintering at 1150 °C for 1 min and 1000 °C for 3 h. In addition, those fine-grained Ga-LLZO exhibit improved stability against molten Li. The Li/Ga-LLZO/Li symmetric cells show a critical current density of 0.7 mA cm −2 , and a stable cycling of over 600 h at 0.4 mA cm −2 at 27 °C. The Li/Ga-LLZO/LiFePO 4 full cells deliver reversible capacity of 150 mAh g −1 , showing negligible decay after 50 cycles. These results bring the Ga-LLZO electrolytes one step closer to practical application in solid-state batteries.

The interrelation of the structure of Al<sub>2</sub>O<sub>3</sub>-ceramics with the mechanism of formation of the surface layer of the workpieces during diamond grinding

The interrelation of the structure of Al2O3ceramics with the roughness and morphology of the polished surface of the samples was established. On this basis, the physical nature of the formation of the surface layer during diamond grinding of fine-grained and coarse-grained ceramics has been revealed. Ill. 2. Ref. 22.

Fine-Grained Tungstates SrWO4 and NaNd(WO4)2 with the Scheelite Structure Prepared by Spark Plasma Sintering

Fine-grained SrWO4 and NaNd(WO4)2 ceramics with the scheelite structure having high relative densities (99 and 95.8%), which can appear candidate matrices for radioactive waste (RAW) management, are prepared by spark plasma sintering (SPS). The phase identity of the ceramics is determined by X-ray powder diffraction; their microstructure is studied by X-ray photoelectron spectroscopy. The tungstates under study are sintered at rather low temperatures (580–665°C). The intensity of compaction of the tungstates at the early sintering stage is determined by the degree of powder agglomeration. The activation energy of fine-grained scheelite ceramics at high temperatures corresponds with the activation energy of grain-boundary oxygen diffusion.

The effect of a barium titanate xerogel precursor on the grain size and densification of fine-grained BaTiO3 ceramics

In this study, we mixed a xerogel precursor of BaTiO3 (X-BTO) prepared by the sol-gel method into identical BaTiO3 powders obtained by co-precipitation during granulation to obtain fine-grained and dense BaTiO3 ceramics at a low sintering temperature (Ts). The effects of X-BTO, Ts, and dwelling time on the grain size and density of the BaTiO3 ceramics showed clear trends, and have predictable effects on the dielectric properties. With increasing X-BTO content, samples underwent a transition from the cubic phase to the tetragonal phase, the mean grain size increased, and the density and maximum dielectric constant first increased and then slightly decreased. Based on the requirements for dense and fine-grained ceramics with particle sizes comparable to powders, the BaTiO3 ceramic with 8 wt% X-BTO sintered at 940 °C exhibited improved permittivity (2445) and acceptable dielectric loss (0.019). This approach makes it possible to control the ceramic grain size by changing the powder's particle size, thereby creating fine-grained and dense BaTiO3 ceramics at a lower Ts.

Dielectric relaxations in fine-grained SrTiO3 ceramics with Cu and Nb co-doping

SrTi1−3x(CuxNb2x)O3 (x = 0.05, 0.1, 0.15 and 0.2) ceramics were synthesized using a solid-state reaction method at 1400 °C in air. Their structures, valence states, conduction mechanisms and dielectric properties were investigated in detail. Fine grains and vibration modes of the samples related to the doping effects were observed. A distorted pseudo-cubic structure was confirmed by XRD and Raman spectroscopy. All ceramics exhibited a colossal dielectric constant and dielectric relaxations. The dielectric constant in the low- and high-frequency ranges for x = 0.05 and 0.1 was ascribed to the contribution of the grain boundary and grain, respectively, and the electrode polarization was significant at x = 0.15 and 0.2. The dielectric relaxation peaks obeyed the T−1/4 law at low temperature for all samples, confirming the polaron relaxation process. The electric modulus analysis confirmed that low-temperature dielectric relaxation was related to the grain response, and the electric conduction exhibited the same behavior with the dielectric relaxation. The variable-range-hopping conduction indicated a highly distorted structure and the localization of carriers in SrTi1−3x(CuxNb2x)O3, which was consistent with the XRD and Raman results. The mixed-valence structure of Cu was identified by XPS, and the polaron hopping between the mixed-valence Cu ions was supposed to be responsible for the dielectric relaxation and electric conduction.

On the origin of grain size effects in Ba(Ti0.96Sn0.04)O3 perovskite ceramics

Over the last 50 years, the study of grain size effects in ferroelectric ceramics has attracted great research interest. Although different theoretical models have been proposed to account for the variation in structure and properties of ferroelectrics with respect to the size of structural grains, the underlying mechanisms are still under debate. Here, we report the results of a study on the influence of grain size on the structural and physical properties of Ba(Ti0.96Sn0.04)O3 (BTS), a ferroelectric compound that represents a model perovskite system, where the effects of point defects, stoichiometry imbalance and phase transitions are minimized by chemical substitution. It was found that different microscopic mechanisms are responsible for the different grain size dependences observed in BTS. High permittivity is achieved in fine-grained BTS ceramics due to high domain wall density and polar nanoregions; high d33 is obtained in coarse-grained ceramics due to a high degree of domain alignment during poling; large electric field-induced strain in intermediate-grained ceramics is an outcome of a favorable interplay between constraints from grain boundaries and reversible reorientation of non-180° domains and polar nanoregions. These paradigms can be regarded as general guidelines for the optimization of specific properties of ferroelectric ceramics through grain size control.

Fabrication of Monodisperse Ba0.80Sr0.20Zr0.10Ti0.90O3@mSiO2 Particles and Fine-Grained Ceramic with Mesoporous SiO2 Coating for Enhanced Energy Storage Properties

Monodisperse submicron Ba0.8Sr0.2Zr0.1Ti0.9O3 (BSZT) particles have been prepared using an aqueous phase method. Cetyltrimethylammonium bromide was used as a template and surfactant to achieve a mesoporous SiO2 shell coating on the surface of the BSZT particles via tetraethoxysilane hydrolysis, resulting in BSZT@mSiO2 particles (where “m” means “mesoporous”) with high dispersibility. A dense, fine-grained BSZT@mSiO2 energy-storage ceramic (with grain size ≤ 280 nm) was obtained by sintering in air at 1050°C for 2 h. The maximum dielectric constant and energy storage density of the BSZT@mSiO2 ceramics were 782 and 0.27 J/cm3, respectively, at room temperature. The mesoporous SiO2 shell of the BSZT@mSiO2 particles improved the dielectric constant and energy storage density of the ceramic compared with a non-mesoporous SiO2 shell. This method therefore represents an interesting approach for preparation of fine-grained energy storage ceramics.

Effects of grain size and temperature on the energy storage and dielectric tunability of non-reducible BaTiO3-based ceramics

BaTiO3-based ceramics with various grain sizes (136–529 nm) are prepared through a chemical coating method followed by sintering in a reducing atmosphere. Effects of grain size and temperature on electric properties, energy-storage properties, and dielectric tunability are studied via Current-Field (J-E) curves, ferroelectric hysteresis loops, Capacitance-Voltage (C–V) curves and Thermally stimulated depolarization currents (TSDC). At all temperatures, fine-grain ceramics yield a lower energy density but a higher energy efficiency under the same electric field, owing to a lower ferroelectric contribution. Meanwhile, fine-grain ceramics exhibit a higher maximum energy density due to their higher breakdown strength. Fine-grain ceramics with the grain size of 136 nm have the maximum energy density of 0.41 J/cm3 under the breakdown strength of 75 kV/cm, the corresponding efficiency is 81%. C–V curves show that fine-grain ceramics have better bias-field stability. According to TSDC results, fine-grain ceramics exhibit fewer oxygen vacancies and a higher relaxation activation energy.

Magnetodynamic Studies of Fine-Crystalline YBa2Cu3Oy High-Temperature Superconductor Samples Synthesized by the Sol–Gel Method

Measurements of the complex magnetic susceptibility as a function of the temperature, alternating field amplitude, and the parallel applied constant field values for a series of YBa2Cu3Oy high-temperature superconductor samples synthesized by two different methods using of the sol–gel technology have been carried out. Regularities in the change of crystalline sizes and critical superconducting parameters are determined depending on the synthesis conditions. For all the samples, both the average temperatures of the transition to the superconducting state and their ranges, which characterize the homogeneity of the sample, remain at the level of the maximum values achievable for this compound. It is concluded that different types of the nanoscale inhomogeneity of the crystalline structure manifest themselves in the differences of the temperature dependences of the transport critical current. Means of further improving the sol–gel method for producing fine-grained ceramics with desired properties are outlined.

Spark Plasma Sintering of fine-grained SrWO4 and NaNd(WO4)2 tungstates ceramics with the scheelite structure for nuclear waste immobilization

Spark Plasma Sintering has been used to obtain first ever fine-grained SrWO4 and NaNd(WO4)2 ceramics with the scheelite structure and high density (95.8–99%) that are promising as materials for nuclear waste immobilization. It has been demonstrated that the densification intensity in tungstates at the initial sintering stage is determined by the agglomeration degree of input powders. The activation energy of fine-grained ceramics with the scheelite structure has been established to correlate at high temperatures with the activation energy of grain-boundary diffusion. Rapid sintering of fine-grained NaNd(WO4)2 ceramic results in internal tensile stress fields that lead to lowered hardness and fracture toughness of the ceramic.