JAC 2020 年第 9 卷第 6 期導讀

為便於讀者查找和閱讀近年來 Journal of Advanced Ceramics 上發表的論文，本公眾號將陸續推出近年來 JAC 各期論文導讀專題。這一導讀將提供每一期所有論文的題目、作者、檢索信息、摘要及全文下載二維碼 (掃描二維碼即可方便地下載論文全文)、全文下載地址。

A review of CoSb3-based skutterudite thermoelectric materialsZhi-Yuan Liu, Jiang-Long Zhu, ... Wen-Yu ZhaoJ. Adv. Ceram., 2020, 9 (6): 647 - 673Abstract: The binary skutterudite CoSb3 is a narrow bandgap semiconductor thermoelectric (TE) material with a relatively flat band structure and excellent electrical performance. However, thermal conductivity is very high because of the covalent bond between Co and Sb, resulting in a very low ZT value. Therefore, researchers have been trying to reduce its thermal conductivity by the different optimization methods. In addition, the synergistic optimization of the electrical and thermal transport parameters is also a key to improve the ZT value of CoSb3 material because the electrical and thermal transport parameters of TE materials are closely related to each other by the band structure and scattering mechanism. This review summarizes the main research progress in recent years to reduce the thermal conductivity of CoSb3-based materials at atomic-molecular scale and nano-mesoscopic scale. We also provide a simple summary of achievements made in recent studies on the non-equilibrium preparation technologies of CoSb3-based materials and synergistic optimization of the electrical and thermal transport parameters. In addition, the research progress of CoSb3-based TE devices in recent years is also briefly discussed.

https://link.springer.com/article/10.1007/s40145-020-0407-4Fabrication, microstructures, and optical properties of Yb:Lu2O3 laser ceramics from co-precipitated nano-powdersZiyu Liu, Guido Toci, .. Jiang LiJ. Adv. Ceram., 2020, 9 (6): 674 - 682Abstract: The Yb:Lu2O3 precursor made up of spherical particles was synthesized through the co-precipitation method in the water/ethanol solvent. The 5 at% Yb:Lu2O3 powder is in the cubic phase after calcination at 1100°C for 4 h. The powder also consists of spherical nanoparticles with the average particle and grain sizes of 96 and 49 nm, respectively. The average grain size of the pre-sintered ceramic sample is 526 nm and that of the sample by hot isostatic pressing grows to 612 nm. The 1.0 mm-thick sample has an in-line transmittance of 81.6% (theoretical value of 82.2%) at 1100 nm. The largest absorption cross-section at 976 nm is 0.96×10E−20 cm2 with the emission cross-section at 1033 nm of 0.92×10E−20 cm2 and the gain cross sections are calculated with the smallest population inversion parameter β of 0.059. The highest slope efficiency of 68.7% with the optical efficiency of 65.1% is obtained at 1033.3 nm in quasi-continuous wave (QCW) pumping. In the case of continuous wave (CW) pumping, the highest slope efficiency is 61.0% with the optical efficiency of 54.1%. The obtained laser performance indicates that Yb:Lu2O3 ceramics have excellent resistance to thermal load stresses, which shows great potential in high-power solid-state laser applications.

https://link.springer.com/article/10.1007/s40145-020-0403-8Fabrication and electrical characteristics of flash-sintered SiO2-doped ZnO-Bi2O3-MnO2 varistorsPai Peng, Yujun Deng, ... Dong XuJ. Adv. Ceram., 2020, 9 (6): 683 - 692Abstract: The dense ZnO-Bi2O3-MnO2-xSiO2 (ZBMS) varistors for x = 0, 1, 2, 3 wt% were fabricated by flash sintering method under the low temperature of 850°C within 2 min. The sample temperature was estimated by a black body radiation model in the flash sintering process. The crystalline phase assemblage, density, microstructure, and electrical characteristics of the flash-sintered ZBMS varistors with different SiO2-doped content were investigated. According to the XRD analysis, many secondary phases were detected due to the SiO2 doping. Meanwhile, the average grain size decrease with increasing SiO2-doped content. The improved nonlinear characteristics were obtained in SiO2-doped samples, which can be attributed to the ion migration and oxygen absorption induced by the doped SiO2. The flash-sintered ZBMS varistor ceramics for x = 2 wt% exhibited excellent comprehensive electrical properties, with the nonlinear coefficient of 24.5, the threshold voltage and leakage current of 385 V·mm−1 and 11.8 µA, respectively.

https://link.springer.com/article/10.1007/s40145-020-0404-7Enhanced ferro-/piezoelectric properties of tape-casting-derived Er3+-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 optoelectronic thick filmsJie Xu, Qiling Lu, ... Xiao WuJ. Adv. Ceram., 2020, 9 (6): 693 - 702Abstract: Er3+-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 (xEr-BCTZ, x = 0, 0.005, 0.01, 0.015) multifunctional thick films were prepared by the tape-casting method, using sol-gel-derived nano-sized powders as the matrix material. The surface morphologies, photoluminescence, and electrical properties were investigated. Dense microstructures with pure perovskite structure were obtained in the thick films. By doping an appropriate amount of Er3−, the samples exhibit superior up-conversion photoluminescence performance and simultaneously enhanced electrical performances. In addition, relatively higher texture fractions (with the largest value of 83.5%) were realized through introducing plate-like BaTiO3 templates to make the thick film grow by the [001]c orientation. And the ferro-/piezoelectric properties of the thick films were further improved, showing potential in the applications of micro-optoelectronic devices.

https://link.springer.com/article/10.1007/s40145-020-0405-6Influence of MoSi2 on oxidation protective ability of TaB2-SiC coating in oxygen-containing environments within a broad temperature rangeXuanru Ren, Junshuai Lv, ... Peizhong FengJ. Adv. Ceram., 2020, 9 (6): 703 - 715Abstract: TaB2-SiC coating modified by different content of MoSi2 was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB2-SiC coatings. As compared to the sample with the TaB2-40wt%SiC coating, the coating sample modified with MoSi2 exhibited a weight gain trend at lower temperatures, the fastest weight loss rate went down by 76%, and the relative oxygen permeability value reduced from about 1% to near 0. More importantly, the large amount of SiO2 glass phase produced over the coating during oxidation was in contact with the modification of MoSi2, which was proved to be beneficial to the dispersion of Ta-oxides. A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration. However, when the TaB2 content was sacrificed to increase the MoSi2 content, the relative oxygen permeability of the coating increased instead of decreased. Thus, on the basis of ample TaB2 content, increasing the MoSi2 content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.

https://link.springer.com/article/10.1007/s40145-020-0406-5Microstructure and mechanical properties of short-carbon-fiber/Ti3SiC2 compositesGuangqi He, Rongxiu Guo, ... Changsheng LiuJ. Adv. Ceram., 2020, 9 (6): 716 - 725Abstract: Short-carbon-fibers (Csf) reinforced Ti3SiC2 matrix composites (Csf/Ti3SiC2, the Csf content was 0 vol%, 2 vol%, 5 vol%, and 10 vol%) were fabricated by spark plasma sintering (SPS) using Ti3SiC2 powders and Csf as starting materials at 1300°C. The effects of Csf addition on the phase compositions, microstructures, and mechanical properties (including hardness, flexural strength (σf), and KIC) of Csf/Ti3SiC2 composites were investigated. The Csf, with bi-layered transition layers, i.e., TiC and SiC layers, were homogeneously distributed in the as-prepared Csf/Ti3SiC2 composites. With the increase of Csf content, the KIC of Csf/Ti3SiC2 composites increased, but the σf decreased, and the Vickers hardness decreased initially and then increased steadily when the Csf content was higher than 2 vol%. These changed performances (hardness, σf, and KIC) could be attributed to the introduction of Csf and the formation of stronger interfacial phases.

https://link.springer.com/article/10.1007/s40145-020-0408-3Surface-modified Zn0.5Ti0.5NbO4 particles filled polytetrafluoroethylene composite with extremely low dielectric loss and stable temperature dependenceHao Wang, Fuming Zhou, ... Qilong ZhangJ. Adv. Ceram., 2020, 9 (6): 726 - 738Abstract: Polymer-ceramic composites are widely applied in microwave substrate materials due to the excellent dielectric properties and simple preparation process recently. Polytetrafluoroethylene-based (PTFE) composites filled with Zn0.5Ti0.5NbO4 (ZTN) ceramic particles were fabricated by hot-pressing. The particles were modified by C14H19F13O3Si to enhance the interface compatibility between PTFE and ZTN powders, which was characterized by X-ray photoelectron spectroscopy (XPS) and contact angle. The surface characteristic of particles transformed into hydrophobicity and tight microstructure as well as better dielectric properties were obtained after the surface modification. The microstructure, dielectric, thermal, mechanical properties, and water absorption of the composites concerning ZTN content were investigated. Modified ZTN/PTFE composites with 50 vol% ZTN particles exhibit excellent dielectric properties with a high dielectric constant of 8.3, an extremely low dielectric loss of 0.00055 at 7 GHz, and a stable temperature coefficient of the dielectric constant of −12.2 ppm/°C. All the properties show modified ZTN particles filled PTFE composite is the potential material for microwave substrate application.

https://link.springer.com/article/10.1007/s40145-020-0409-2Microstructural evolution and mechanical properties of in situ nano Ta4HfC5 reinforced SiBCN composite ceramicsBingzhu Wang, Daxin Li, ... Chenguang GaoJ. Adv. Ceram., 2020, 9 (6): 739 - 748Abstract: The in situ nano Ta4HfC5 reinforced SiBCN-Ta4HfC5 composite ceramics were prepared by a combination of two-step mechanical alloying and reactive hot-pressing sintering. The microstructural evolution and mechanical properties of the resulting SiBCN-Ta4HfC5 were studied. After the first-step milling of 30 h, the raw materials of TaC and HfC underwent crushing, cold sintering, and short-range interdiffusion to finally obtain the high pure nano Ta4HfC5. A hybrid structure of amorphous SiBCN and nano Ta4HfC5 was obtained by adopting a second-step ball-milling. After reactive hot-pressing sintering, amorphous SiBCN has crystallized to 3C-SiC, 6H-SiC, and turbostratic BN(C) phases and Ta4HfC5 retained the form of the nanostructure. With the in situ generations of 2.5 wt% Ta4HfC5, Ta4HfC5 is preferentially distributed within the turbostratic BN(C); however, as Ta4HfC5 content further raised to 10 wt%, it mainly distributed in the grain-boundary of BN(C) and SiC. The introduction of Ta4HfC5 nanocrystals can effectively improve the flexural strength and fracture toughness of SiBCN ceramics, reaching to 344.1 MPa and 4.52 MPa·m1/2, respectively. This work has solved the problems of uneven distribution of ultra-high temperature phases in the ceramic matrix, which is beneficial to the real applications of SiBCN ceramics.

https://link.springer.com/article/10.1007/s40145-020-0410-9Synthesis and electrochemical properties of V2C MXene by etching in opened/closed environmentsMeng Wu, Yan He, ... Aiguo ZhouJ. Adv. Ceram., 2020, 9 (6): 749 - 758Abstract: The effect of etching environment (opened or closed) on the synthesis and electrochemical properties of V2C MXene was studied. V2C MXene samples were synthesized by selectively etching of V2AlC at 90°C in two different environments: opened environment (OE) in oil bath pans under atmosphere pressure and closed environment (CE) in hydrothermal reaction kettles under higher pressures. In OE, only NaF (sodium fluoride) + HCl (hydrochloric acid) etching solution can be used to synthesize highly pure V2C MXene. However, in CE, both LiF (lithium fluoride) + HCl and NaF+HCl etchant can be used to prepare V2C MXene. Moreover, the V2C MXene samples made in CE had higher purity and better-layered structure than those made in OE. Although the purity of V2C obtained by LiF+HCl is lower than that of V2C obtained using NaF+HCl, it shows better electrochemical performance as anodes of lithium-ion batteries (LIBs). Therefore, etching in CE is a better method for preparing highly pure V2C MXene, which provides a reference for expanding the synthesis methods of V2C with better electrochemical properties.

https://link.springer.com/article/10.1007/s40145-020-0411-8Synthesis, microstructure, and properties of high purity Mo2TiAlC2 ceramics fabricated by spark plasma sinteringYunhui Niu, Shuai Fu, ... Chunfeng HuJ. Adv. Ceram., 2020, 9 (6): 759 - 768Abstract: The synthesis, microstructure, and properties of high purity dense bulk Mo2TiAlC2 ceramics were studied. High purity Mo2TiAlC2 powder was synthesized at 1873 K starting from Mo, Ti, Al, and graphite powders with a molar ratio of 2:1:1.25:2. The synthesis mechanism of Mo2TiAlC2 was explored by analyzing the compositions of samples sintered at different temperatures. It was found that the Mo2TiAlC2 phase was formed from the reaction among Mo3Al2C, Mo2C, TiC, and C. Dense Mo2TiAlC2 bulk sample was prepared by spark plasma sintering (SPS) at 1673 K under a pressure of 40 MPa. The relative density of the dense sample was 98.3%. The mean grain size was 3.5 μm in length and 1.5 μm in width. The typical layered structure could be clearly observed. The electrical conductivity of Mo2TiAlC2 ceramic measured at the temperature range of 2–300 K decreased from 0.95 × 106 to 0.77 × 106 Ω–1·m–1. Thermal conductivity measured at the temperature range of 300–1273 K decreased from 8.0 to 6.4 W·(m·K)–1. The thermal expansion coefficient (TEC) of Mo2TiAlC2 measured at the temperature of 350–1100 K was calculated as 9.0 × 10E–6 K–1. Additionally, the layered structure and fine grain size benefited for excellent mechanical properties of low intrinsic Vickers hardness of 5.2 GPa, high flexural strength of 407.9 MPa, high fracture toughness of 6.5 MPa·m1/2, and high compressive strength of 1079 MPa. Even at the indentation load of 300 N, the residual flexural strength could hold 84% of the value of undamaged one, indicating remarkable damage tolerance. Furthermore, it was confirmed that Mo2TiAlC2 ceramic had a good oxidation resistance below 1200 K in the air.

https://link.springer.com/article/10.1007/s40145-020-0412-7Thermoelectric performance enhancement by manipulation of Sr/Ti doping in two sublayers of Ca3Co4O9Li Zhang, Yichen Liu, ... Sean LiJ. Adv. Ceram., 2020, 9 (6): 769 - 781Abstract: Thermoelectric (TE) performance of Ca3Co4O9 (CCO) has been investigated extensively via a doping strategy in the past decades. However, the doping sites of different sublayers in CCO and their contributions to the TE performance remain unrevealed because of its strong correlated electronic system. In this work, Sr and Ti are chosen to realize doping at the [Ca2CoO3] and [CoO2] sublayers in CCO. It was found that figure of merit (ZT) at 957 K of Ti-doped CCO was improved 30% than that of undoped CCO whereas 1 at% Sr doping brought about a 150% increase in ZT as compared to undoped CCO. The significant increase in electronic conductivity and the Seebeck coefficient are attributed to the enhanced carrier concentration and spin-entropy of Co4+ originating from the Sr doping effects in [Ca2CoO3] sublayer, which are evidenced by the scanning electron microscope (SEM), Raman, Hall, and X-ray photoelectron spectroscopy (XPS) analysis. Furthermore, the reduced thermal conductivity is attributed to the improved phonon scattering from heavier Sr doped Ca site in [Ca2CoO3] sublayer. Our findings demonstrate that doping at Ca sites of [Ca2CoO3] layer is a feasible pathway to boost TE performance of CCO material through promoting the electronic conductivity and the Seebeck coefficient, and reducing the thermal conductivity simultaneously. This work provides a deep understanding of the current limited ZT enhancement on CCO material and provides an approach to enhance the TE performance of other layered structure materials.

https://link.springer.com/article/10.1007/s40145-020-0413-6Microstructure and mechanical properties of Ti3(Al,Ga)C2/Al2O3 composites prepared by in situ reactive hot pressingYuan Fang, Xiaohua Liu, ... Wei JiangJ. Adv. Ceram., 2020, 9 (6): 782 - 790Abstract: In this study, Ti3(Al,Ga)C2/Al2O3 composites were successfully synthesized by in situ hot pressing at 1350 °C for 2 h using Ti, Al, TiC, and Ga2O3 as raw materials. X-ray diffraction and scanning electron microscopy were used for characterizing the phase identities and microstructures of the sintered composites. The dependence of the Vickers hardness and flexural strength on the Al2O3 content was found to be in single-peak type. Ti3(Al0.6,Ga0.4)C2/10.3vol%Al2O3 composite exhibited significantly improved mechanical properties. Vickers hardness and flexural strength of the composite reached 6.58 GPa and 527.11 MPa, which were 40% and 74% higher than those of Ti3AlC2, respectively. Formation of solid solution and incorporation of second phase of Al2O3 resulted in the opposite influence on the fracture toughness. Finally, the hardening and strengthening mechanisms were discussed in detail.

https://link.springer.com/article/10.1007/s40145-020-0428-z
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