CaMnxZr(1-x)O3: A novel NTC thermo-sensitive ceramic for applications in a wide temperature range

The perovskite CaMn_xZr_(1-x)O₃ (x = 0, 0.05, 0.10, 0.15) (CMZO) NTC (Negative Thermal Coefficient) thermo-sensitive ceramic were prepared by the solid phase method that can be used as high temperature thermistor materials in the range of 200–1200 °C.The XRD pattern showed that CMZO is a finite solid solution and that a second phase, CaMnO₃, will be formed after exceeding the solid solution limit (i.e., at x = 0.1). The thermal constant B value was found to decrease from 19521 K to 9217–9535 K, with a corresponding decrease in activation energy, E_a, from 1.69 eV to 0.82 eV. The Nyquist plot indicates that the grain boundary resistance determines the overall complex impedance. Moreover, the aging drift rate (ΔR/R₀) was found to be lower than 4.3%, which is an indication of an excellent high temperature stability of the CMZO ceramic material.     

Al2O3-SiC复相陶瓷材料制备方法的研究现状

简要论述了Al2O3-SiC复相陶瓷材料的常用制备方法,如无压烧结法、热压烧结法、气压烧结法和溶胶-凝胶法等,重点介绍了碳热还原法。对以不同原料制备Al2O3-SiC复相陶瓷材料的碳热还原法进行了比较,指出了这方面研究的不足之处和下一步研究的方向。     

Suppressed temperature dependence of the resonant frequency of a AgNb0.5Ta0.5O3 composite vs. single-phase ceramics

AgNb_0.5Ta_0.5O₃ ceramics were synthesized and analyzed, with respect to their dielectric properties, in the radio- and microwave-frequency ranges. The influences of different synthesis conditions were investigated and correlated with the difficulties in preparing single-phase ceramics, as a consequence of the inhomogeneous distribution of Nb and Ta ions and the decomposition of the matrix phase. The results revealed that with the simple mixing of all three oxides and subsequent firing in air, it is possible to prepare composite material that is attractive for microwave applications due to inhomogeneity of the B-site cation distribution – a well-known issue that was in our case shown to be an advantage for decreasing the temperature dependence of the resonant frequency over a broad temperature range. On the other hand, we also succeeded in fabricating single-phase ceramics with a very high density through the initial formation of a precursor and sintering in an overpressure of oxygen.     

Shrinkage features,microstructure evolution and properties of Gd2O3-MgO optical composite ceramics with Zr as phase stabilizer

A novel composite ceramic, composed of equal-volumetric Zr-stabilized Gd₂O₃ and MgO phases, was prepared to be transparent in mid-wave infrared range. Zr stabilized Gd₂O₃ is proved to have a lower lattice parameter (10.7516 Å) using XRD refinement. Pressureless sintering behavior of Gd₂O₃-MgO with/without 2 at% Zr-doping (naming ZGM and GM) was studied via the real-time observation technique. The shrinkage of ZGM green body proceeds steadily up to 1400 °C while that of the undoped one shrinks sharply at 1250 °C due to Gd₂O₃ phase transition. The segregation of Zr element along the grain boundaries of Zr-Gd₂O₃ creates a synergized effect on the grain refinement with pinning effect. Dense ZGM ceramics exhibit superior transmittance of 78.3 %‐85.6 % at 3–5 µm, which show good consistency with the calculated values. The refractive index of Zr- Gd₂O₃ varies from 1.87 at 3 µm to 1.80 at 5 µm, which is smaller than those of monoclinic Gd₂O₃.     

烧结气氛对合成MgAl2O4-Ti(C,N)复合陶瓷的影响

以金属铝粉、钛白粉和轻烧MgO细粉为原料,通过设计100%焦炭粒(简称C气氛),10%钛白粉 90%焦炭粒(简称TC气氛),以及10%硅微粉 90%焦炭粒(简称SC气氛)3种埋粉条件下的高温烧结还原性气氛,采用X射线衍射仪(XRD)、扫描电镜(SEM)和微区电子探针分析(EPMA)等手段,研究了铝热还原氮化法(1600℃3h)制备MgAl2O4-Ti(C,N)复合陶瓷在不同烧结气氛下的相组成和显微结构的变化。结果表明在不同气氛下,烧后试样的主要物相均为MgAl2O4和Ti(C,N),Ti(C,N)可能会固溶氧,气氛对Ti(C,N)的影响较大。和单纯埋炭气氛下相比,在TC气氛下有助于Ti(C,N)的生成,但晶粒细小;在SC气氛下不利于Ti(C,N)的生成,且有玻璃相存在。     

Effect of magnetic CoFe2O4 component on sintering densification process of Bi3.15Nd0.85Ti3O12 ceramics

Sintering densification processes of the composite ceramics (Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT)/CoFe₂O₄ (CFO)) have been investigated using dilatometric experiments combining with the TG-DTA, density measurements and microstructure studies. Microstructures analyses and quantitative calculations show that the composite ceramics achieve densification at low temperatures (<1150 °C). The formation of coherent-lattice interfaces between (200)/(020)_BNdT and (310)_CFO are considered to play an important role on such densification. The intrinsic preferred orientation of BNdT grains is suppressed by CFO phase because of this coherent relationship. Although the sintering activation energies of 0.8BNdT-0.2CFO are about 2.7 times larger than those of pure BNdT due to the pinning effect, the composite ceramic could still be densified, indicating the formation energy of coherent-lattices provided the extra sintering force. The even coercive electric fields of the resulting pure BNdT and 0.8BNdT-0.2CFO ceramic are approximately 89 and 97 kV/cm, respectively, at 250 kV/cm. The polarization of 0.8BNdT-0.2CFO reaches saturation around 430 kV/cm.     

High recoverable energy storage density in nominal (0.67-x)BiFeO3-0.33BaTiO3-xBaBi2Nb2O9 lead-free composite ceramics

A series of novel lead-free energy storage ceramics, (0.67-x)BiFeO₃-0.33BaTiO₃-xBaBi₂Nb₂O₉ (BF-BT-xBBN), were fabricated by traditional solid-state reaction, where bismuth layer-structured BaBiNb₂O₉ was incorporated into perovskite-structured BiFeO₃–BaTiO₃ ceramic as an additive. The addition of BaBi₂Nb₂O₉ increased the relaxor behavior and breakdown strength of BF-BT ceramics due to the formation of polar nanoregionals (PNRs), inducing enhanced energy storage performance. The composite ceramics, with x = 0.08, showed a large recoverable energy density (W_rec) of 3.08 J/cm³ and an outstanding energy storage efficiency (η) of 85.57% under an applied electric field of 230 kV/cm. Moreover, the composite ceramics exhibited excellent thermal stability and high stability toward different frequencies in a temperature range of 20–100 °C and a frequency range of 0.1–1500 Hz. These results demonstrate great potential of novel BF-BT-xBBN composite ceramics for next-generation energy storage applications.     

Effect of Fe3O4 concentration on 3D gel-printed Fe3O4/CaSiO3 composite scaffolds for bone engineering

In this study, porous calcium silicate (CaSiO₃) scaffolds were prepared by 3D gel-printing (3DGP) method and Fe₃O₄ water-based magnetic fluids (WMFs) were prepared by phacoemulsification compound chemical coprecipitation method. Fe₃O₄ WMFs were coated on CaSiO₃ scaffolds surface to prepare Fe₃O₄/CaSiO₃ composite scaffolds. The effect of WMFs with different Fe₃O₄ concentrations on porous CaSiO₃ scaffolds was studied. The composition and morphological characteristics of porous scaffolds were analyzed by using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis. The magnetic properties were tested by vibrating sample magnetometer (VSM). The stability of Fe₃O₄ WMFs coatings and the degradability of composite scaffolds were tested by immersing them in simulated body fluid (SBF). The results show that when Fe₃O₄ concentration was 5.4% (w/v), the composite scaffolds had the highest saturation magnetization of 69.6 emu/g and the best stability in dynamic SBF. It is obviously that Fe₃O₄ WMFs coatings can be used for bone tissue engineering scaffolds repairing.     

In situ synthesis of Si2N2O/Si3N4 composite ceramics using polysilyloxycarbodiimide precursors

In situ synthesis of Si₂N₂O/Si₃N₄ composite ceramics was conducted via thermolysis of novel polysilyloxycarbodiimide ([SiOSi(NCN)₃]_n) precursors between 1000 and 1500 °C in nitrogen atmosphere. The relative structures of Si₂N₂O/Si₃N₄ composite ceramics were explained by the structural evolution observed by electron energy-loss spectroscopy but also by Fourier transform infrared and ²⁹Si-NMR spectrometry. An amorphous single-phase Si₂N₂O ceramic with porous structure with pore size of 10–20 μm in diameter was obtained via a pyrolyzed process at 1000 °C. After heat-treatment at 1400 °C, a composite ceramic was obtained composed of 53.2 wt.% Si₂N₂O and 46.8 wt.% Si₃N₄ phases. The amount of Si₂N₂O phase in the composite ceramic decreased further after heat-treatment at 1500 °C and a crystalline product containing 12.8 wt.% Si₂N₂O and 87.2 wt.% Si₃N₄ phases was obtained. In addition, it is interesting that residual carbon in the ceramic composite nearly disappeared and no SiC phase was observed in the final Si₂N₂O/Si₃N₄ composite.     

Low-loss and temperature stable (1-x)Ba3P2O8-xMg2B2O5 composite ceramics with low sintering temperature

In this study, the Ba₃P₂O₈ and Mg₂B₂O₅ were fabricated by the solid-state reaction method separately, and the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ (x = 0.2–0.4) low-temperature co-fired ceramic (LTCC) materials were obtained in the sintering temperature range of 880–960 °C. The phase compositions, microstructures, elemental compositions, and microwave dielectric properties of the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ composite ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and TE_01δ mode dielectric resonator method, respectively. The results revealed that the Mg₂B₂O₅ phase and Ba₃P₂O₈ phase could coexist well in the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ composite ceramics without formation of any new phases. The abnormal grain growth of Ba₃P₂O₈ grains was inhibited by the addition of Mg₂B₂O₅. In addition, through composition of Ba₃P₂O₈ and Mg₂B₂O₅, the temperature coefficient of resonant frequency (τ_f) and quality factor (Q×f) were effectively optimized, and the sintering temperature was reduced to 880–960 °C. The optimal performance of 0.8Ba₃P₂O₈-0.2Mg₂B₂O₅ composite ceramic was achieved at a sintering temperature of 920 °C, τ_{f =} ?1.9 ppm/°C, Q×f = 61,250 GHz, and a low permittivity ε_r = 10.7. The chemical compatibility test demonstrated that the composite ceramic could coexist well with silver, which indicated that the 0.8Ba₃P₂O₈-0.2Mg₂B₂O₅ composite ceramic is a candidate LTCC material with wide application prospects.     

0-3 type magnetoelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3:CoFe2O4 composite ceramics with a deferred thermal depolarization

Developing Na_0.5Bi_0.5TiO₃-based magnetoelectric (ME) coupling composites with higher depolarization temperature is highly valuable for the environment-friendly smart electronic devices. We have developed a new kind of 0-3 type 0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃:xCoFe₂O₄ (NBTBT:xCFO, x = 0, 0.1, 0.2, 0.3) composite ceramics with a deferred depolarization temperature, together with an additional strong ME coupling of 9.2 mV/cm·Oe for the NBTBT:0.2CFO. The basic structure, ferroelectric/ferromagnetic properties, and the depolarization temperature of the NBTBT:xCFO composite ceramics were investigated. It was found that an enhancement of depolarization temperature (>25 °C) was obtained in these 0-3 type composites relative to the pure NBTBT ones (115 °C vs 90 °C). The mechanism of the enhanced depolarization temperature of the composites is discussed. The present results demonstrate that NBTBT:xCFO composites have great potential for ME devices.     

溶胶凝胶法合成La_(0.7)Sr_(0.3)Fe_(0.8)Co_(0.2)O_3影响因素的研究

以合成中温固体氧化物燃料电池阴极La0.7Sr0.3Fe0.8Co0.2O3(LSFC)粉体为研究对象,探讨了PVA改进的溶胶凝胶法合成粉体的影响因素,获得最优实验条件。当pH值=7,柠檬酸与金属离子摩尔比为1.6∶1;PVA与硝酸盐质量比为1∶4时,能够形成形态良好且透明澄清的溶胶,再经12 h的陈化形成凝胶,然后在155℃烘箱中使凝胶膨化制得LSFC前驱体。LSFC前躯体在900℃煅烧2 h后形成晶体结构稳定、粒径分布均匀、具有单一钙钛矿结构的粉体。     

Formation of closed pore structure in CaO-MgO-Al2O3-SiO2 (CMAS) porous glass-ceramics via Fe2O3 modified foaming for thermal insulation

Due to the low density, low thermal conductivity and low water absorption, porous glass-ceramics have demonstrated excellent performance for thermal insulation. Closed pore structure can greatly reduce the thermal conductivity and convection as well as achieve high mechanical strength. However, yet it is difficult to realize closed pore structure due to the critical preparation condition. Here we use Fe₂O₃, which is the by-product of copper tailings, to optimize the pores structures of the porous glass-ceramics and facilitate the formation of uniform closed pore structure. The porous glass-ceramics were prepared by melting-quenching method, followed by sufficiently foaming through powder sintering route with SiC powders as foaming agent. The foaming process, micro structure, pore structure and thermal insulation performance were directly observed by heating microscope, scanning electron microscope (SEM), X-ray computed tomography and infrared thermal imager. The results show that the addition of Fe₂O₃ modified the depolymerization degree of the glass network and increased the numbers of non-bridged oxygen, decreasing the foaming temperature. The resultant closed pore structure showed a better thermal insulating performance than open pore structure. Accordingly, we achieved a low thermal conductivity of 0.19 W·m^?1·K^?1 with the highest specific strength of 19.55 MPa·g^?1·cm^?3 based on closed pore structure.     

Effects of spark plasma sintering on ferroelectricity of 0.8Bi3.15Nd0.85Ti3O12-0.2CoFe2O4 composite ceramic

The 0.8Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT)-0.2CoFe₂O₄ (CFO) composite multiferroic ceramics have been fabricated by spark plasma sintering (SPS) at 850?°C. The relative density of as-sintered SPS ceramic reaches 97.4 (±0.3)%. The composites are composed of pure BNdT and CFO phases without any preferred c-orientation. The a-orientation preference is more obvious perpendicular to the pressure direction. The average grain-sizes of BNdT and CFO are 163 and 146?nm, respectively. The BNdT phase has more grains below 100?nm (～20%). The super energy-dispersive X-ray analyses suggest no serious reaction between BNdT and CFO. The Raman spectrum verifies the nano-structure of the SPS ceramic via the broadening bands and peak shifts. The Curie temperature of the SPS ceramic declines to 560?°C with stabilized dielectric loss. The grain boundary resistance plays a dominant role on impedance above 700?°C. The remanent polarization approaches to 15.2?μC/cm² (300?kV/cm) with lower coercive fields (?89/+95?kV/cm).     

Effect of atmosphere control on magnetic properties of CaO-Al2O3-SiO2-Fe3O4 glass ceramics

The influences of atmosphere during processes of melting and heat treatment, heat treatment temperature, Fe₃O₄ content and basicity on the magnetic properties of magnetite-based glass ceramics were investigated. For sample containing 20 % Fe₃O₄ melted in different atmospheres, the highest saturation magnetisation was realized in 20vol% air + 80 vol% Ar, due to the fact that ratio of Fe³⁺ to Fe²⁺ in melt obtained in this atmosphere was close to 2. However, it was found that the coercivity of glass ceramics was not affected by the melting atmosphere. A high sintering temperature led to the decrease of saturation magnetisation and the increase of coercivity. As increasing Fe₃O₄ content, the main crystal phase transformed from CaSiO₃ to CaFe_0.6Al_1.3Si_1.08O₆ and finally to magnetite phase, accompanied by the increase of saturation magnetisation and coercivity. In addition, the increase of basicity caused the decrease of saturation magnetisation and the increase of coercivity.     

热压烧结Al2O3-ZrB2-SiC复相陶瓷的高温力学性能研究

为提高Al2O3陶瓷的高温力学性能,采用热压烧结工艺(烧结温度1 800℃,烧结压力20 MPa,保温1 h)制备了Al2O3-ZrB2-SiC复相陶瓷(简称AZS),并研究了ZrB2含量对Al2O3基陶瓷高温抗折强度和抗热震性的影响。结果表明:1)在Al2O3基陶瓷中加入第二相ZrB2能有效改善材料的高温抗折强度和高温强度保持率,在1 000和1 200℃时,加入20%体积分数ZrB2的AZS陶瓷试样具有最高的高温抗折强度,而加入24%体积分数ZrB2的AZS陶瓷试样具有最高的高温强度保持率。2)AZS陶瓷的抗热震性能优于纯Al2O3陶瓷。经100℃温差急冷后,加入20%体积分数ZrB2的AZS陶瓷具有最高的残余强度,比纯Al2O3陶瓷提高了17.2%;经300和500℃温差急冷后,加入24%体积分数ZrB2的AZS陶瓷都具有最高的残余强度,比Al2O3陶瓷分别提高了35.3%和20.9%。     

Influence of the processing way for La3+-doping on crystal structure,microstructure, and microwave dielectric properties of Ca0.7Ti0.7La0.3Al0.3O3 ceramics

Perovskite ceramics with a formula of Ca_0.7Ti_0.7La_0.3Al_0.3O₃ (CTLA) were produced through a conventional solid-state reaction procedure following three different La³⁺-doping methods using powders of La₂O₃, or La₂O₃/Al₂O₃ powder mixture, or LaAlO₃. La³⁺ doping favored grain growth and densification, affected the grain size distribution, and improved the dielectric properties of the produced sintered CTLA ceramics. The doping methods had a strong influence on these properties. More specifically, doping with La₂O₃ and La₂O₃/Al₂O₃ resulted in formation of solid solution, while a secondary phase formed in the CTLA ceramics doped with LaAlO₃, which caused a coarsening of the microstructure and lowered the La³⁺ doping effects on the dielectric properties. The experimental results suggest that La³⁺ doping improves the dielectric properties of the sintered CTLA perovskite ceramics, which are further enhanced by doping with Al³⁺ ions in small amounts. However, further increase of Al³⁺ ions content jeopardizes them.     

Enhanced energy storage property in glass-added Ba(Zr0.2Ti0.8)O3-0.15(Ba0.7Ca0.3)TiO3 ceramics and the charge relaxation

Glass additive BaO-SrO-TiO₂-Al₂O₃-SiO₂-BaF₂ is employed to enhance the microstructures and energy storage properties of the Ba(Zr_0.2Ti_0.8)O₃-0.15(Ba_0.7Ca_0.3)TiO₃ ceramics. To clarify the energy storage mechanism, the charge transportation and polarization process are investigated by thermally simulated depolarization current (TSDC). The dielectric breakdown strength increases from 4.3?kV/mm to 10.8?kV/mm for BZT-0.15BCT ceramics with 11?wt% glass additives, indicating that glasses could refine the grain size, uniform the structure, and decrease defects. Due to the micro-domain region, dielectric relaxation behavior is observed with a broadened and reduced dielectric constant peak at a large dielectric constant of about 3000?at room temperature. The largest charge energy density of 1.45?J/cm³ and discharge density of 0.17?J/cm³ are achieved for BZT-0.15BCT glass ceramics with 7?wt% glass additives. TSDC results demonstrate that dipole origin movement and charge transportation have an important effect on the dielectric properties and dielectric breakdown strength, respectively, which are largely influenced by the defects distribution state at the interfaces. Moderate domain walls could restrain the defects to inhibit the charge transportation and are harmful for the dielectric properties inversely. To achieve excellent energy storage performance, moderate domain walls are compromise of slightly degrading dielectric properties and greatly improving dielectric breakdown strength.     

Influence of Cr3+ substitution for Mg2+ on the crystal structure and microwave dielectric properties of CaMg1-xCr2x/3Si2O6 ceramics

The CaMg_1-xCr_2x/3Si₂O₆ (0?≤?x?≤?0.1) microwave dielectric ceramics were synthesized via conventional solid state reaction. In this study, the effects of Cr³⁺ substituting for Mg²⁺ on morphology, crystal structure and microwave dielectric properties of CaMg_1-xCr_2x/3Si₂O₆ ceramics were explored. XRD diffraction patterns exhibited that the CaMg_1-xCr_2x/3Si₂O₆ ceramics possessed the pure phase of CaMgSi₂O₆ when x?≤?0.06 and a small amount of secondary phase Ca₃Cr₂(SiO₄)₃ for 0.08?≤?x?≤?0.1. SEM micrographs revealed that the substitution of Mg²⁺ with Cr³⁺ could decrease the grain size. The apparent density was affected by the concentration of Mg vacancies. The correlation between crystal structure and microwave dielectric properties was investigated through the Rietveld refinement and Raman analysis. The microwave dielectric properties were mainly dependent on relative density, ionic polarizabilities, internal strain ?, disordered structure and MgO₆ octahedron distortions. Finally, CaMg_1-xCr_2x/3Si₂O₆ (x?=?0.02) ceramics sintered at 1270?°C for 3?h exhibited excellent microwave dielectric properties of ε_r?=?8.06, Q?×?f?=?89054?GHz, τ_f?=??44.92182?ppm/ºC.     

Preparation of fully dense and magnetically controllable CaO-Al2O3-SiO2-Na2O-Fe3O4 glass ceramics by hot pressing

Fully dense and magnetically controllable glass ceramics was successfully synthesized by method of hot pressing using CaO-Al₂O₃-SiO₂-Na₂O glass powder and Fe₃O₄ powder as raw materials. The influences of sintering temperature and time, content and particle size of Fe₃O₄, as well as particle size of glass powder on the densification and magnetic properties of samples were investigated. It was found that the saturation magnetization gradually increased with increasing magnetite content. In addition, the samples containing smaller size magnetite particles had a higher coercivity. However, for samples using smaller size glass powder, magnetite particles could partially dissolve into the glass matrix, which led to the decrease of saturation magnetization and the increase of coercivity. It was also concluded that the precipitation of crystalline phase from smaller size glass powder caused the decrease of degree of densification, and after decreasing the sintering temperature, the degree of densification of product was enhanced.