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Grain growth mechanism and thermoelectric properties of hot press and spark plasma sintered Na-doped PbTe
摘要： We investigated he thermoelectric (TE) properties and microstructures of Na-doped PbTe compounds, synthesized by various milling and sintering processes. It has been generally accepted that spark plasma sintering (SPS) inhibits grain growth due to the short sintering time, which is bene?cial to the nano bulk composite. In contrast, we observed abnormal grain growth for SPS, unlike hot press (HP) sintering. Considering the Gibbs free energy change during sintering, the HP sintering increases internal energy while the SPS increases entropy energy, which causes the abnormal grain growth. Lattice strain and Fourier transform analyses of the transmission electron microscope images showed that the SPS sintered samples had more signi?cant lattice strains and defects than the HP sintered samples. The low thermal conductivity of the SPS sintered samples was not from grain boundary phonon scattering but from phonon scattering by lattice strains and defects. The lattice strains and defects decreased electrical conductivity as well, resulting in deterioration of the power factor and thermoelectric performance. This suggests that the lattice strains and defects are more critical factors for enhancing thermoelectric per- formance than particle and grain size control.
关键词： Grain growth,Thermoelectric,Hot press,Spark plasma sintering,ZT
更新于2025-11-21 10:59:37
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Dielectric tunable properties of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics prepared by spark plasma sintering
摘要： Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics were prepared by spark plasma sintering (SPS) technique and their phase composition, microstructures and dielectric tunable properties were studied. With increasing Mg2TiO4?MgO content, the dielectric peaks of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics were broadened and suppressed. The tunability of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics first increased and then decreased with the increase of Mg2TiO4?MgO content. For Mg2TiO4?MgO content ≤ 50 wt%, Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics showed higher tunability and lower permittivity than pure Ba0.5Sr0.5TiO3, which can be attributed to the suppression of the doping effect by SPS. The contradiction between reduced permittivity and enhanced tunability in ferroelectric-dielectric composites was resolved.
关键词： Dielectrics,Ferroelectric ceramics,Spark plasma sintering,Composites
更新于2025-11-14 17:28:48
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The effect of pre-annealing and post-annealing on the transparency of MgAl2O4, prepared by slip casting and spark plasma sintering (SPS)
摘要： The aim of this paper is to investigate the effect of slip casting process and the annealing before and after sintering to achieve a transparent MgAl2O4. To remove contaminants such as carbon from the structure of shaped spinel bodies, at first, the samples were annealed at temperature of 800 °C, 900 °C and 1000 °C for 2 h and then sintered at 1400 °C. By annealing the sample before sintering at 900 °C, the transmission increased (15% at IR region and 10% at visible region). Although by annealing the samples, the amount of carbon contamination reduced. Annealing the samples after sintering also had some desirable results. The samples annealed at temperature of 1200 °C for a time of 3, 5 and 10 h. The darkness of samples reduced due to the removal of carbon impurities and the sample was annealed at 1200 °C for 5 h had the most transparency in the visible and infrared regions.
关键词： Spark plasma sintering,Slip casting,MgAl2O4,Annealing,Transparency
更新于2025-09-23 15:23:52
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The Impact of Peltier Effect on the Temperature Field During Spark Plasma Sintering of Thermoelectric Materials
摘要： We report about the modelling of spark plasma sintering of a line of thermoelectric materials. A significant difference of sintering temperature DTs from 15 K to 110 K was found in the samples studied. The Peltier effect on the graphite-thermoelectric interfaces results in such temperature difference. The rise of sintering temperature leads to the DTs increase. DTs in the vertical direction is 2–3 times higher than in the radial one. Electric insulation modelled in the horizontal graphite–thermoelectric interfaces reduced DTs in all the types of numerically studied samples by 59–92%.
关键词： spark plasma sintering,FEM,SPS,Thermoelectrics,finite elements simulation
更新于2025-09-23 15:22:29
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Residual porosity and optical properties of spark plasma sintered transparent polycrystalline cerium-doped YAG
摘要： Transparent cerium-doped yttrium aluminum garnet (Ce:YAG) phosphors are promising candidates for high-power white light emitting diode applications. In the present study, Ce:YAG powder was synthesized by a co-precipitation method and highly transparent ceramics were fabricated by spark plasma sintering. The effects of temperature and pressure, as well as post-sintering treatments (annealing or hot isostatic pressing), on residual porosity were studied by electron and confocal laser microscopy. Correlation between residual porosity characteristics (pore size and volume fraction) and optical properties (in-line transmittance and photoluminescence intensity) of the luminescent transparent ceramics was established.
关键词： Transparency,Spark plasma sintering,Photoluminescence,Ce:YAG ceramic,Residual porosity
更新于2025-09-23 15:21:21
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Hydrogen reduction behavior and microstructural characteristics of WO3 and WO3-NiO powders
摘要： The characterization and understanding of the hydrogen reduction and sintering behavior of powder mixtures prepared from WO3 and WO3-NiO have been investigated. The nano-sized W and W-Ni powders were prepared by ball milling and hydrogen reduction of oxide powders. The reduction behavior is analyzed by temperature-programmed reduction method with different heating rates in Ar-10% H2 atmosphere. X-ray diffractometry analysis revealed that the oxide powders are changed to W and W-Ni powders with an average particle size of about 100 nm by hydrogen reduction at 800oC for 1 h. The hydrogen reduction kinetics was evaluated by the amount of peak shift with heating rates. The activation energies for the reduction of pure WO3 and WO3-NiO, estimated by the slope of the Kissinger plot, were measured as 87.4–117.4 kJ/mol depending on reduction steps. The consolidated W-Ni by spark plasma sintering has relatively dense and large grains with neck growth by enhanced mass transport due to the addition of Ni. These results are help to optimize the powder synthesis process and to understand the hydrogen reduction behavior and Ni addition effect related to microstructure of powders and sintered bodies.
关键词： Hydrogen reduction behavior,Microstructure,Metal oxides,W and W-Ni,Spark plasma sintering
更新于2025-09-23 15:19:57
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Nanostructuring of dense SnO2 ceramics by Spark Plasma Sintering
摘要： The spark plasma sintering (SPS) behaviour of pure SnO2 has been studied. Two different SnO2 powders have been studied: a commercial 50–200 nm one and 4–6 nm nanoparticles obtained by precipitation. It has demonstrated that it is not possible to keep pure SnO2 above 1223 K by SPS. Indeed, at 1248 K, SnO appears whereas at higher temperatures, samples are composed by SnO2 and metal Sn. Three different cycles have been developed that allow achieving high densities (≥94%). The study of the grain size shows that when the density increases the grain size increases to reach 60–70 nm for the high density samples. Therefore, SPS can be successfully used to produce dense nanostructured SnO2 ceramics without any sintering agent. Nanostructuring is very efficient to lower thermal conductivity as values as low as 6.59 and 3.99 W m?1.K?1 at 373 and 1000 K respectively, are measured in SPS nanostructured ceramics. Moreover, the transport properties of the dense ceramics are the best reported for undoped SnO2.
关键词： Spark plasma sintering,Tin oxide,Thermal conductivity,Thermoelectric,Nanostructuring
更新于2025-09-19 17:15:36
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Morphology control of nanostructure using microsphere-assisted femtosecond laser double-pulse ablation and chemical etching
摘要： In order to adjust the mismatch of coe?cient of thermal expansion between NbSi2 coating and Nb alloy while suppressing the pest oxidation of NbSi2 coating at moderate temperatures, NbSi2-Si3N4 composite coatings with doped Ti and Al were prepared on Nb alloy by a spark plasma sintering process using an Nb-Si-Si3N4-Ti-Al powder mixture. The sintering reactions based on the thermodynamic feasibility for the constituent phase formation of the coatings were revealed, and the oxidation resistance of the coatings at 750 °C was investigated. The coatings had a multiple-phase structure and mainly consisted of (Nb,Ti)Si2, Si3N4, (Ti,Nb)5Si4, (Nb,Ti)5Si3, and a small number of other nitride phases. After 50 h of oxidation, pest oxidation was observed on both the NbSi2 coating and NbSi2-Si3N4 coating, while no indication of pest oxidation was present on the coatings after doping with Ti and Al.
关键词： Oxidation-resistant coating,Microstructure,Sintering behavior,Spark plasma sintering
更新于2025-09-19 17:13:59
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Spark plasma sintering of Sb2Se3 sputtering target towards highly efficient thin film solar cells
摘要： Antimony selenide (Sb2Se3) is a potential absorber material for environment-friendly and cost-efficiently photovoltaics due to its material advantages and superior optoelectronic properties. In this work, we proposed a facile and versatile method of ball milling followed with spark plasma sintering (SPS) to prepare high-quality Sb2Se3 sputtering target. Then the highly crystalline Sb2Se3 thin film consisted of large crystal grains can be prepared by using radio frequency (RF) magnetron sputtering with an additional post-selenization heat treatment. An efficient substrate structured Sb2Se3 thin film solar cell with configuration of Mo/Sb2Se3/CdS/ITO/Ag was fabricated and a champion device with highly interesting power conversion efficiency (PCE) of 5.08% has been achieved. Superior device performances are closely related to the Sb2Se3 absorber layer with benign growth orientation and the Sb2Se3/CdS heterojunction interface with smooth contact, which induced less recombination loss. The combined features of homemade sputtering target and advantageous thin film preparation technology further demonstrated its attractive application potential in thin film photovoltaic scenarios.
关键词： Sb2Se3,Post-selenization,Sputtering target,Magnetron sputtering,Spark plasma sintering,Thin film solar cells
更新于2025-09-19 17:13:59
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High-Brightness and High-Power Laser Welding of Powder Metallurgy Shape Memory Alloy: Welding-Parameter-Dependent Microstructure
摘要： Despite the growing interest in using powder metallurgy shape memory alloys, there is limited research on their joining and welding aiming to expand their applications. In this research, we utilized a high-power, high-brightness disk laser welding process to join spark-plasma-sintered Ti-51 at.% Ni shape memory alloy and studied the primary factors that affect the strength and functionality of the created sound welds such as intermetallics and martensite (B19￠) phase formation. The introduction of high-power laser could impede the formation of B19￠ and undesirable intermetallics such as TiNi3 and Ti2Ni; however, the desired Ti3Ni4 would also be suppressed and post-weld heat treatment was necessary to induce them again. The microstructure of fusion zones was significantly altered, producing coarse columnar grains with centerline and equiaxed weld centers. Additionally, high-power laser welding of powder metallurgy Ti-Ni alloy triggered amorphous phase formation in the welds due to rapid cooling. It was found that a laser power of 3 kW and welding speed of 6 m/min are optimal welding parameters, since the produced weld solidified along favorable [001] direction of strain recovery in Ti-Ni shape memory alloys.
关键词： disk laser welding,microstructural characterization,shape memory alloys,spark plasma sintering
更新于2025-09-16 10:30:52