Ca0.7Ti0.7La0.3Al0.3O3微波介质陶瓷微观组织结构与介电性能

采用固相反应法制备斜方晶系钙钛矿结构Ca07Ti07La0.3Al0.3O3微波介质陶瓷,研究了Al3+、Ca2、Ba2+和La3+离子掺杂对CTLA陶瓷微观组织结构和介电性能的影响.研究结果表明不同掺杂离子对于CTLA陶瓷的微观结构和介电性能有很大的影响,不同离子掺杂CTLA陶瓷的晶粒尺寸、气孔率、晶界析出相有很大的不同.Al3+、Ca2+、Ba2+和La3+离子掺杂可以有效降低CTLA陶瓷的谐振频率温度系数,但Ca2+、Ba2+离子掺杂同时也降低了CTLA陶瓷的致密度和Q×f值,Al3+、La3+离子掺杂不仅有效提高了CTLA陶瓷的致密度和Q×f值,并且有效降低了谐振频率温度系数.适量掺杂La3离子可以有效促进CTLA陶瓷的致密化,提高了CTLA陶瓷的微波介电性能.掺杂0.15mol％ La3+的CTLA陶瓷在4.7 GHz下测试介电性能为:εr=48.39,Q×f=32560 GHz,τf=23.68 ppm/C.     

MnCoNiO陶瓷材料制备及其电学特性研究

采用固相反应法制备Mn_1.47Co_(1.095-X)Ni_(0.435+X)O_4(X=0~0.343)热敏陶瓷。利用XRD、SEM以及电性能测试等手段表征了陶瓷相组成、微观结构和材料的电学特性。结果表明:当Ni含量≤0.484(x=0.049)时,陶瓷体为单一尖晶石结构,并且随着Ni含量的增加,衍射峰强度逐渐增强;当Ni含量≥0.533(x=0.098)时,出现Mn_2O_3衍射峰,且随着Ni含量的进一步增加,Mn_2O_3衍射峰强度增强,尖晶石衍射峰强度减弱,陶瓷体为尖晶石和Mn_2O_3混合相。在1150℃到1250℃烧结温度范围内,通过调节Ni元素含量,Mn_1.47Co_(1.095-X)Ni_(0.435+X)O_4陶瓷室温电阻率从1815.3Ω·cm变化到171439Ω·cm。     

Ni–Mn–Sn–O体系相组成及其在负温度系数热敏电阻中的应用

采用固相法制备Ni–Mn–Sn–O系单相尖晶石结构化合物。使用X-射线衍射技术确定了该体系的成相范围和温度,并判定该尖晶石结构的阳离子分布。结果表明:Ni元素摩尔含量在15%以下时,形成四方尖晶石相;在15%~30%之间时形成立方尖晶石相;大于30%时则易析出NiO相。Sn元素的含量对成相温度有重要影响,其含量越多,成相温度越高。但当Sn元素含量达到30%以上时,则不能进入尖晶石结构中。Sn元素以Sn4+的形式占据尖晶石结构中的B位,导致其电阻率和热敏常数B值急剧增加。     

过渡金属氧化物掺杂钛酸钡取代位置及价态的研究

从BaTiO3的晶体结构出发,分析了固溶能和晶格畸变对不同价态的过渡金属离子掺杂BaTiO3时取代位置的影响。分析结果表明:Ti4+离子在BaTiO3晶体结构中具有一定的几何松散度,Cr3+、Fe3+、Co3+和Ni2+离子半径与Ti4+的接近,取代Ti位的固溶能均较小;大量实验结果表明,掺杂前后晶格常数的变化与取代Ti位的理论结果相吻合;过渡金属(Cr、Fe、Co和Ni)氧化物掺杂BaTiO3时分别以Cr3+、Fe3+、Co3+和Ni2+取代Ti位掺杂。确定某种贱金属氧化物在BaTiO3中的具体取代位置对制备抗还原的贱金属内电极的BaTiO3基MLCC有重要意义。     

Nd2O3掺杂对BCZT陶瓷结构及介电性能的影响

采用固相反应法制备Ba0.92-xCa0.08Ndx(Zr0.18Ti0.815Y0.0025Mn0.0025)O3(BCZT-Nd,x=0、0.005、0.010、0.020)陶瓷,研究了Nd2O3掺杂对Ba0.92Ca0.08(Zr0.18Ti0.82)O3(BCZT)陶瓷结构及介电性能的影响。结果表明,不同含量Nd3+作为施主掺杂离子进入A位和含量均为0.25%(摩尔分数)的Mn2+和Y3+作为受主掺杂进入B位均能提高BCZT陶瓷的致密性,细化晶粒作用明显,所有样品均为单一的四方BaTiO3相结构。随Nd2O3掺杂量增加,BCZT-Nd陶瓷介电峰值温度Tm向低温方向移动,相变弥散程度增强,Nd3+含量≥0.005mol时即表现出明显的弛豫铁电体特征。     

ZrO2和SnO2复合掺杂对贫铁配方的MnZn铁氧体磁性能和电性能的影响

通过ZrO2与SnO2复合掺杂制备了低损耗的MnZn铁氧体材料.研究了在贫铁配方的基础上添加SnO2-ZrO2对MnZn铁氧体微观结构、电性能以及磁性能的影响.结果表明,适量的SnO2-ZrO2复合掺杂有利于促进晶粒均匀致密,明显提高了材料的电阻率,降低比损耗因子,在ξ(SnO2:ZrO2)为3:1时材料的电阻率达到最大值29.5 Ωm,比损耗因子达到最小值4.8×10-6.复合掺杂还能提高材料的居里温度、饱和磁感应强度和起始磁导率,当ξ(SnO2:ZrO2)为3:1时磁性能都达到最佳.     

Zn2+掺杂对0.965MgTiO3-0.035SrTiO3微波介质陶瓷结构与性能影响研究

采用固相反应法制备了0.965 MgTiO3-0.035SrTiO3 (MST)微波介质陶瓷,选用Zn2+对MST陶瓷进行了A位离子掺杂,研究了不同Zn2+掺杂量对陶瓷烧结性能、晶相组成、显微结构及微波介电性能的影响.结果表明,Zn2的掺入促进了陶瓷的烧结,显著提高了陶瓷的致密度,且没有改变陶瓷的主晶相.在掺杂量小于0.04mol％范围内,随着Zn2+掺杂量的增加,陶瓷的介电常数增加,品质因素和频率温度系数略有降低.中间相MgTi2 O5的衍射峰强度随着Zn2+掺杂量的增加逐渐减弱直至完全消失.当Zn2掺杂量为x=0.03时,陶瓷的烧结温度由1380℃降低至1290℃,并呈现优异的微波介电性能:εr=22.51,Q×f=16689 GHz,τf=-4.52×10-6/℃.     

Er掺杂对CaMnO_3陶瓷的微观结构及高温电性能的影响

以混合硝酸盐为原料,采用共沉淀法结合常压压片和1200℃烧结制备出钙位掺杂Er的Ca_(1-x)Er_xMnO_3(x=0,0.02,0.04,0.06,0.10)热电陶瓷,采用XRD和SEM对所有样品进行相结构和微观形貌表征,同时测定Ca_(1-x)Er_xMnO_3系列样品的电阻率,Seebeck系数。研究钙位掺杂Er元素对CaMnO_3材料的微观结构和高温电性能的影响。XRD及SEM分析结果表明,采用共沉淀法制备出的Ca_(1-x)Er_xMnO_3热电陶瓷物相单一,材料内部结构致密。电性能测试结果表明,Er掺杂可以有效的改善CaMnO_3的电输运性能,当Er掺杂量为0.10,温度为973K时最大功率因子为2.95×10~(-4)Wm-1K~(-2),是未掺杂CaMnO_3的1.5倍。     

锑锰掺杂对Pb_(0.80)Ca_(0.20)TiO_3陶瓷显微结构及性能的影响

以Ca CO3、Sb2O3、Pb3O4、Ti O2、Mn CO3为原料,采用传统固相法制备Pb0.80Ca0.20Ti O3陶瓷,研究了掺入2%~10%(摩尔分数)的Sb2/3Mn1/3对Pb0.80Ca0.20Ti O3陶瓷显微结构、电阻率、介电性能、热释电性能的影响。结果表明:当Sb2/3Mn1/3掺杂量≤5%时为单一钙钛矿相,晶粒随掺杂量的增大而减小,致密性逐渐变好。当Sb2/3Mn1/3掺杂量5%时,陶瓷为钙钛矿和焦绿石两相混合物,致密性和晶粒均匀性变差。加入Sb2/3Mn1/3后,陶瓷电阻率数量级由108增加到1012,介电损耗大幅降低,热释电系数增大,探测率优值Fd显著提高。在Sb2/3Mn1/3掺杂量为5%时,获得了高电阻率、综合热释电性能良好、晶粒尺寸小的热释电陶瓷材料。     

铈掺杂镍锌铁氧体的制备与性能研究

用高分子凝胶法制备了稀土元素铈掺杂的镍锌铁氧体粉Ni0.5Zn0.5CexFe2-xO4,并对产物结构和电磁性能进行了表征。结果表明,当Ce3+的掺杂摩尔数x为0.1时,800℃煅烧后会形成立方晶系尖晶石结构的镍锌铁氧体晶相。与Ni0.5Zn0.5Fe2O4铁氧体相比,在8.2~12.4 GHz频率范围内掺杂铈元素的Ni0.5Zn0.5Ce0.1Fe1.9O4铁氧体的tanδm值降低,而其tanδe值升高,平均值可达0.527。     

Co2O3/Co3O4掺杂量对BaBiO3基热敏陶瓷NTC特性的影响

采用X射线衍射、扫描电子显微镜和ρ-t特性测试仪,研究了不同Co2O3/Co3O4掺杂量对BaCoⅢxBi1-xO3(x=0.02, 0.04, 0.06, 0.08) 和BaCoⅡx/3CoⅢ2x/3Bi1-xO3(x=0.02, 0.04, 0.06, 0.08)热敏陶瓷的物相、显微结构及电性能的影响.结果表明:BaCoⅢxBi1-xO3和BaCoⅡx/3CoⅢ2x/3Bi1-xO3的基本相均为钙钛矿结构的连续固溶体;Co2O3/Co3O4的含量能直接影响电学性能.试样的室温电阻率ρ25和B25~85值均随着Co2O3/Co3O4的增加呈现先下降后回升的趋势;BaCoⅢ0.06Bi0.94O3陶瓷展现出较好的NTC特性,其ρ25和B25~85值分别为12.19 Ω·cm和717 K;BaCoⅡ0.02CoⅢ0.04Bi0.94O3也获得了良好的NTC特性,其ρ25和B25~85值分别为12.32 Ω·cm和1069 K.     

Core–shell NTC materials with low thermal constant and high resistivity for wide-temperature thermistor ceramics

Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al₂O₃-modified Co_1.5Mn_1.2Ni_0.3O₄ NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co_1.5Mn_1.2Ni_0.3O₄ powder was coated with a thin Al₂O₃ shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al₂O₃ layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ ceramic with 0.08 wt% Al₂O₃ showed the increase of ρ double, and the change in its B was less than 140 K. The Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics.     

BaTiO3系PTCR材料电学性能的复阻抗解析

采用复阻抗解析法研究了ＢａＴｉＯ３系ＰＴＣＲ材料晶粒、晶界的电学性能。结果表明：使用欧姆接触电极的ＰＴＣＲ材料等效电路的复阻抗为：晶粒电阻呈ＮＴＣ特性，而晶界电阻天Ｔ〈Ｔｃ时呈ＮＴＣ特性，Ｔ〉Ｔｃ时呈明显的ＰＴＣ特性；ＰＴＣ效应是一种晶界效应。     

Preparation and sealing effects of Mg–Al–Si–Ba–O-based glass-ceramic coatings on NTC thermistors

Herein, Mg–Al–Si–Ba–O-based glass ceramics were studied as potential candidates to protect Mn–Co–Ni–O-based negative temperature coefficient (NTC) thermistors at high temperatures such as 900 °C. The ceramics were prepared in three glass formulations (1#: 15MgO–15Al₂O₃-44.7SiO₂–25BaO, 2#: 17MgO–17Al₂O₃–41SiO₂–25BaO and 3#: 17MgO–17Al₂O₃–41SiO₂–20BaO–5Y₂O₃ (in mol%)) and their glass-transition temperatures (T_g) were determined using the differential scanning calorimetry (DSC) method. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the parent glasses and glass-ceramic coatings. The sealing effects of the glass ceramics were examined by conducting an insulation test. The glass-ceramic sealing structures were subjected to 1000 thermal shock cycles at temperatures varying from room temperature to 900 °C. Notably, the sealing structure of glass-ceramic coating 1# was compact at a T_g of 760.9 °C. The glass-ceramic coatings effectively maintained the NTC properties of the sensitive ceramics in all three formulations. Interestingly, the glass-ceramic coating 3# containing Y₂O₃ demonstrated an increase in electrical resistance. Both the NTC thermistors coated with 1# and 2# glass formulations successfully passed 1000 thermal shock cycles without visible failures, and their resistance change ratios were well below the requisite 20%.     

Optimizing the stability and electrical transport properties of CeNbO4+δ-based oxide ceramics by regulating oxygen ion content

CeNbO_4+δ ceramics have attracted extensive research interest because of their unique mixed ion-electron transport characteristics and interesting structure-functional characteristics caused by the difference in oxygen ion content. Although the change of oxygen ion content brings rich redox properties, it also causes serious crystal transformation and abnormal electrical transport properties. In order to obtain stable structure and excellent electrical transport properties, the directional regulation of the oxygen ion content has been realized through introducing Al₂O₃ and high temperature aging. After 600 h of aging at 1073 K, the prepared composite ceramics not only obtain a stable structure without crystal transformation, but also show good negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K–1273 K, in which the linear fitting maximum Pearson's r of the relationship between lnρ and 1000/T can reach 99.97%. The proposed method provides a new thought for the design and application of high-temperature electronic ceramics.     

Sintering properties and homogeneity of Ca2+-doped .65Y2O3–.35YCr0.5Mn0.5O3 NTC ceramics

Ceramics suitable for use over a wide temperature and having a negative temperature coefficient (NTC) based on .65Y₂O₃–.35YCr_0.5Mn_0.5O₃-doped with CaO were prepared by applying a solid-state reaction at different temperatures (1500–1650°C). The physical properties and scanning electron microscopy results revealed that dense NTC ceramics could be obtained by sintering at >1550°C. The effect of two different sintering methods on the properties of the NTC ceramics was studied, and the results indicated that the NTC ceramics obtained by employing the two-step sintering method exhibited better properties. The contents of Cr and Mn oxides in the NTC ceramic discs prepared by applying two-step sintering (1600°C) exhibited a decreasing trend from inside to outside. To quantify the diffusion rate, Fick's second law was used, and the diffusion coefficients of Cr and Mn oxides in the NTC ceramics were found to be 5.20 × 10^–5 and 2.36 × 10^–5 cm²/s, respectively. Resistivity and temperature analyses indicated that the resistivity (ρ₂₅), B_25/100, and B_700/1000 of the NTC ceramics were 1.61 × 10⁶ Ω cm, 2367 K, and 2697 K, respectively, which are suitable for a wide temperature range.     

Nd1-xSrxMnO3 (x = 0.3): A perovskite manganite ceramic that exhibits PTC and NTC double properties

Nd_1-xSr_xMnO₃ (NSMO, x = 0.280, 0.300, 0.330, 0.350, and 0.375) polycrystalline ceramics were fabricated using the sol-gel method. The crystal structure, surface morphology, valence state, elements distribution, and electrical properties were examined to understand the effect of Sr doping on NdMnO₃ ceramics. The resistivity of the NSMO ceramics was measured using a standard four-probe method. The results obtained revealed that Sr doping significantly decreased the resistivity of the ceramics, which can be explained by the double exchange (DE) interaction and small-polaron hopping (SPH) model. The Nd_0.70Sr_0.30MnO₃ ceramic had a positive temperature coefficient (PTC) of resistivity (16.69% K^?1) at 197.5 K, and is expected to be used for preparing electronic switches with high sensitivity. Additionally, the NSMO ceramics maintained a stable negative temperature coefficient (NTC) of resistivity (?1% K^?1) for x = 0.300 in the temperature range of 210.6–342.5 K. In conclusion, it is worth exploring materials with a high PTC and NTC over an extended temperature range, possessing the double potential function for high sensitivity or wide-temperature detection for electronic switches or infrared bolometers.     

Microstructural and electrical changes in Ca0.9R0.1CeNbMoO8 (R = Y,Sm, Nd,La) ceramics induced by rare-earth ion doping

Rare-earth ions doped Ca_0.9R_0.1CeNbMoO₈ (R = Y, Sm, Nd, La) ceramics have been successfully prepared by solid-state method, and their modifications to the microstructure and electrical properties are also investigated. The rare-earth ions doped ceramics exhibit the scheelite structure. With the increase in the radius of rare-earth ions, the lattice distortion and bond interaction will be enhanced, and the consistency of grain size will be reduced. The ceramics exhibit negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K-1273 K, and the activation energy decreases with the increase of the radius of rare-earth ions. Rare-earth ions doping can increase the content of Ce³⁺ ions and promote the conductivity of ceramics. Except for Sm³⁺-doped ceramics, the high-temperature aging rate of other ceramics is less than 2%. The existence of some metastable Sm²⁺ ions in Sm³⁺-doped ceramics not only increases the activation energy, but also reduces the high-temperature stability of the ceramics.     

Vacancy defects reducing the accuracy and reliability of NTC sensors

The negative temperature coefficient (NTC) thermal sensor has received much attention for temperature sensing, which aims to achieve accurate temperature measurement by using the electrical signal generated by its temperature change. The perovskite (1-x)CaMn_0.05Zr_0.95O₃-xCaMnO₃ (x = 0, 0.1, and 0.2) composite ceramics were reported for the first time. Furthermore, their structure, microscopic morphology, and device performance were systematically evaluated. It was revealed that the sensor performance could be tuned by controlling the CaMnO₃ ratio in the low resistance phase. The phase structure and crystal structures (cell volume and cell parameters a, b, and c) of the composite ceramics were defined using x-ray diffraction (XRD) refinement. Scanning electron microscopy (SEM)/Mapping revealed dense and uniform micromorphology. The ln(ρ) and 1000/T were quite linear, and the aging drift rate was as low as 1.89% after aging at 900 °C for 600 h. Importantly, a novel double hopping mechanism and a cation vacancy defect diffusion model were proposed to reveal the electron transport mechanism in the sensor lattice and elaborate the physical mechanism of the effect of cation vacancy defects on sensor resistance drift. In conclusion, this study prepared an NTC thermal sensor with ultra-high stability in a high temperature environment by rational design, providing a fresh idea for subsequently developing a high temperature NTC sensor.     

A study of V-shaped PTC behaviour of Sr0.4Pb0.6TiO3 ceramics

Yttrium-doped Sr_0.4Pb_0.6TiO₃ ceramics were prepared at relatively low sintering temperature using conventional sintering technology. The sintered ceramics exhibit novel NTC–PTC composite effects. The influences of doping PbO and SiO₂ on the properties of Sr_0.4Pb_0.6TiO₃ ceramics were compared. It was found that suitable PbO additives reduce the room-temperature resistivities (ρ_RT) of Sr_0.4Pb_0.6TiO₃ ceramics and weaken their NTC effects, but the effect of doping SiO₂ is reverse. The XRD analyses show that SiO₂ additives can cause Pb²⁺ ions segregating out from Sr_0.4Pb_0.6TiO₃ lattices and form PbO·SiO₂ phase. It is estimated that the strong NTC effects of Sr_0.4Pb_0.6TiO₃ ceramics should be closely related to the Pb²⁺ immigration. The domain structure, morphology and compositional distribution of Y-doped Sr_0.4Pb_0.6TiO₃ ceramics were investigated using TEM, SEM and EDAX respectively. The results of EDAX indicate that the Pb/Sr ratio on the grain boundaries is slightly lower than that in the grains. According to the results, the V-shaped PTC behaviors of (Sr,Pb)TiO₃ ceramics are discussed.