Jincheng Yao

Formation of Mn‐Co‐Ni‐O Nanoceramic Microspheres Using In Situ Ink‐Jet Printing: Sintering Process Effect on the Microstructure and Electrical Properties

Mn-Co-Ni-O nanoceramic microspheres with high density, uniformity, and size tunability are successfully fabricated using in situ ink-jet printing and two step sintering (TSS) techniques. The microspheres, synthesized by an effective and facile reverse microemulsion method, consist of uncalcined Mn-Co-Ni-O nanocrystallines that show a well formed single tetragonal spinel phase and an average particle size distribution of ≈20 nm. The sintering behavior, microstructure, and electrical properties of the Mn-Co-Ni-O nanoceramic microspheres are systematically investigated and characterized. The results indicate that the sintered Mn-Co-Ni-O nanoceramic microspheres show high density and improved electrical properties. The highest R25 , B25/50 , Ea , and α25 values achieved at sintering temperature of 1150 °C are 4846.7 KΩ, 4320 K, 0.401 eV, and -5.24% K-1 , respectively for these Mn-Co-Ni-O nanoceramic microspheres. Furthermore, the formation mechanism of uncalcined Mn-Co-Ni-O nanocrystallines and an analysis of the TSS procedure of the nanoceramic microspheres are discussed.

High performance of Ni0.9Mn1.8Mg0.3O4 spinel nanoceramic microbeads via inkjet printing and two step sintering

We report a simple and effective in situ inkjet printing method for the fabrication of nanostructured and highly dense Ni0.9Mn1.8Mg0.3O4 (NMM) spinel oxide nanoceramic microbeads materials. In our method, the ceramic inks are fabricated that single cubic spinel NMM nanocrystallines synthesized via co-precipitation method, disperse well in organic solution, and have shown perfect dispersibility and stability. After inkjet printing using these ceramic inks, NMM microbeads are sintered via two-step sintering (TSS) process at different temperatures. The sintering behavior, microstructure and electrical properties of NMM nanoceramic microbeads prepared via TSS process are investigated and characterized systematically. These results indicate that high performance of NMM microbeads with moderate resistance values (98 331–174 601 Ω), lower thermal time constant (58–147 ms), and higher material constant (4176–4309 K) are achieved by tuning the sintering temperatures.

Growth mode and properties of Mn-Co-Ni-O NTC thermistor thin films deposited on MgO (100) substrate by laser MBE

Mn1.56Co0.96Ni0.48O4-δ thin films were deposited on MgO (100) substrate using laser molecular beam epitaxy (LMBE) technique at the temperature range of 300–600°C under oxygen partial pressure of 5 × 10-3 Pa. The effect of growth temperature on microstructure and electrical properties as well as the growth mode were studied using XRD, RHEED, AFM and resistance–temperature measurements. The results showed that all prepared thin films underwent epitaxial growth along the single-(100) orientation direction of the MgO substrate from 3D-island mode to 2D layer-by-layer mode, and exhibited good crystallinity and NTC thermistor behavior. Their resistance at room temperature can be in the range of 10–50 MΩ together with a B-value of about 3300 K, which are desirable for a wide range of practical applications of the NTC thermistors.

Microstructure and Electrical Properties of Mn 2.25-x Ni 0.75 CoxO 4 Thermistor Ceramics: Microstructure and Electrical Properties of Mn 2.25-x Ni 0.75 CoxO 4 Thermistor Ceramics

A series of composite of the negative temperature coefficient (NTC) powders of Mn2.25-xNi0.75CoxO4 (0.8&lex&le1.2) materials were prepared via solid-state method. The particle size of calcined powders, ceramics phase structure, morphology and electrical properties were characterized by laser particle size analyzer, XRD, SEM and electrical measurements, respectively. The results show that when the Mn2.25-xNi0.75CoxO4 ceramics sintered at 1130-1230°C, their characteristic parameters B25/50 value are found to be in the range of 3487 K to 4455 K and their electrical resistivities ρ25°C are 1998 Ω·cm to 203617 Ω·cm. The B25/50 value and ρ25°C first increases and then decreases as the Co content increases. This means that electrical resistivity and B value of Mn2.25-xNi0.75CoxO4 ceramics could be adjusted to the desired values and this ternary system can be considered as the advanced semi-conducting materials for NTC thermistor applications.采用氧化物固相法制备Mn 2.25- x Ni 0.75 Co x O 4 (0.8≤ x ≤1.2)系列NTC(negative temperature coefficient)热敏电阻粉体材料. 利用激光粒度分析、XRD、SEM和电性能测试等手段, 表征了煅烧材料的颗粒尺寸、陶瓷体的物相、形貌以及陶瓷材料的电学特性与Co含量的关系. 结果表明: 在1130~1230℃烧结温度范围内, 该材料体系的B值和电阻率ρ25℃随Co含量的变化范围分别为3487~4455 K和1998~203617 Ω·cm, B值和电阻率随Co含量的增加先增大后减小. 该材料系列电阻率和B值调整范围较大, 是一种具有实际应用价值的NTC热敏电阻.

effect of la2o3 addition on the microstructure and electrical properties of copper-nickel manganese thermistors

The effect of La2O3 addition on the microstructure and electrical properties of Mn0.75Ni1.25CuO4-xLa2O3 (0≤x≤0.3) was studied. The crystal structure, phase compositions and morphology were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The sintered ceramic bodies was typical polycrystalline, with cubic spinel structure of copper manganese oxide, rocksalt structure of nickel copper oxide, along with monoclinic phase of copper oxide and orthorhombic perovskite structure of lanthanum manganese oxide. The obtained ρ77K, B77K/90K constant and activation energy of the thermistors were in the range of 3.88-9.29 Ω cm, 245-261 K, and 0.0211–0.0225 eV, respectively. This means that the electrical properties can be adjusted to desired values, depending on the La content. So these prepared thermistors were intended to be used under low temperature conditions.