铌酸钾钠/铁酸钴铜多铁性磁电复合材料的制备及性能研究

通过固相法制备了(1–x)(0.9462K0.5Na0.5NbO3-0.0498LiSbO3-0.004BiFeO3)-xCo0.85Cu0.15Fe2O4((1–x)(KNN-LS-BFO)-xCCFO)(x=0.1、0.2、0.3、0.4、0.5)复合多铁性磁电陶瓷.XRD分析表明:烧结后的样品为复合的钙钛矿和尖晶石结构,没有发现杂相产生.SEM照片显示KNN-LS-BFO晶粒生长完好尺寸较大,而CCFO晶粒尺寸较小.当x从0.1增加到0.5时,复合材料的压电系数从120 pC/N减小到33 pC/N,而饱和磁化强度和剩磁增加,饱和磁致伸缩系数从18×10–6增加到51.5×10–6左右.材料的磁电耦合系数随着外磁场的增加先增大到极大值后再减小;当交变磁场频率为1 kHz,x=0.3时材料的磁电电压系数达到最大值20.6 mV/A.     

Ba_(0.8)Sr_(0.2)TiO_3/CoFe_2O_4异质结层状多铁复合薄膜的制备与性能

利用射频磁控溅射法在Pt(200)/TiO_2/SiO_2/Si(100)衬底上沉积Ba_(0.8)Sr_(0.2)TiO_3/CoFe_2O_4异质结层状多铁磁电耦合复合薄膜。Ba_(0.8)Sr_(0.2)TiO_3/CoFe_2O_4异质结复合薄膜为多晶,由钙钛矿Ba_(0.8)Sr_(0.2)TiO_3相和尖晶石CoFe_2O_4相组成。复合薄膜表现为良好的铁电性和铁磁性共存。在测量磁场平行于样品表面情况下测得的复合薄膜的饱和磁化强度(M_s)、剩余磁化强度(M_r)值要大于在测量磁场垂直于样品表面时测得的M_s、M_r值。另外,复合薄膜具有直接的磁电耦合效应,磁电电压系数αE先随着偏置磁场H_(dc)的增大而增大,当偏置磁场H_(dc)增加到445.8kA/m后,αE反而随偏置磁场的增加而减少。当偏置磁场H_(dc)=445.8kA/m时,复合薄膜具有最大的磁电电压系数αE=18.8mV/A。     

锂离子电池正极材料LiMn_(0.5)Ni_(0.5-x)Co_xO_2的制备及电化学性能

以氢氧化物共沉淀法合成前驱体,氢氧化锂为锂源,通过高温煅烧合成了锂离子电池正极材料LiMn_(0.5)Ni_(0.5-x)Co_xO_2(x=0、0.1、0.2)。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、恒电流充放电测试、循环伏安法(CV)及电化学交流阻抗谱(EIS)技术对制备条件和钴掺杂量进行了研究。结果表明,所制材料均具有良好的α-NaFeO_2层状结构;当pH=10.5,煅烧温度为850℃,x=0.1时,所制备LiMn_(0.5)Ni_(0.4)Co_(0.1)O_2材料0.2C放电容量达155mAh/g,5C放电容量仍达110mAh/g,0.2C倍率下循环50次后的容量保持率达98%。     

xCoAl_(0.2)Fe_(1.8)O_4+(1-x)BaTiO_3纳米磁电复合材料的磁、介电和磁电特性研究

采用溶胶-凝胶方法制备了xCoAl0.2Fe1.8O4+(1-x)BaTiO3纳米磁电复合材料.XRD图谱分析表明烧结后的样品是复合的钙钛矿(BaTiO3)和尖晶石(CoAl0.2Fe1.8O4)结构,SEM图像显示复合材料颗粒大小均匀.用磁滞回线研究了材料的磁性能,并通过Koops双层异质结构模型解释了复合材料的介电频散现象.测量结果表明:0.20CoAl0.2Fe1.8O4+0.80BaTiO3的样品在偏置磁场为1.35×105A/m时表现出最大的磁电电压系数1.075×10-2 V/A.     

压电/磁致伸缩/环氧树脂层合复合材料的磁电效应及其频响特性

磁电复合材料在磁-电能量转换等领域具有重要的潜在应用价值, 研究磁电复合材料在较高频率下的磁电耦合特性对于实际应用具有重要意义。本文中以0-3型的Terfenol-D(Tb_0.30Dy_0.70Fe₂)/环氧树脂复合材料为磁致伸缩层, 以PZT 压电陶瓷为压电层, 制备了三明治结构的层合磁电复合材料。研究了Terfenol-D/环氧树脂复合材料层的磁致伸缩性质, 并对所制备的层合磁电复合材料磁通密度、 介电常数以及磁电电压系数等随频率和偏磁场的变化规律进行了系统研究。结果表明, 由于Terfenol-D/环氧树脂复合材料的引入, 层合磁电复合材料呈现出良好的频率响应特性, 可靠工作范围大大拓宽。层合磁电复合材料具有优良的动态磁电耦合性能, 在优化偏磁场630 Oe和共振频率69.6kHz下的磁电效应高达21.2 V/cmOe。此外, 层合磁电复合材料的磁电效应随偏磁场的变化发生明显变化, 并存在优化偏磁场。对上述现象和结果进行了详细讨论, 并给出了层合磁电复合材料的磁电耦合机制。      

(Mo_(1/2)Sr_(1/2))~(4+)掺杂Bi_(1/2)Na_(1/2)TiO_3无铅压电陶瓷结构及其性能研究

采用传统陶瓷制备工艺制备出了Bi1/2Na1/2Ti1-x(Mo1/2Sr1/2)xO3(简称BNT-MS-100x)系无铅压电陶瓷材料,研究了(Mo1/2Sr1/2)4+掺杂量对BNT基陶瓷材料显微结构和电学性能的影响。研究结果表明,(Mo1/2Sr1/2)4+掺杂并未影响BNT陶瓷的晶体结构,仍为纯钙钛矿型结构,而且致密性良好。随着(Mo1/2Sr1/2)4+掺杂量增加,居里温度升高,剩余极化强度先增大后减小。当x=0.004时,BNT-MS-100x陶瓷的压电系数最大,d33=104pC/N,介电损耗最小,tanδ=4.11%。     

高居里温度BaTiO3-(Bi0.5Na0.5)TiO3无铅正温度系数电阻陶瓷的制备

用传统的固相反应烧结法制备了(1-xmol%)BaTiO₃-xmol%(Bi_0.5Na_0.5)TiO₃(BBNTx)高温无铅正温度系数电阻( positive temperature coefficient of resistivity, PTCR)陶瓷。X射线衍射表明所有的BBNTx陶瓷形成了单一的四方钙钛矿结构。SEM分析结果显示随着BNT含量的增加, 陶瓷晶粒尺寸减小。空气中烧结的0.2mol% Nb掺杂的BBNT1陶瓷, 室温电阻率为~10² Ω·cm, 电阻突跳为~4.5个数量级, 居里温度为~150℃。氮气中烧结的0.3mol% Nb掺杂的BBNTx(10≤x≤60)陶瓷, 同样具有明显的PTCR效应, 居里温度在180~235℃之间。随着BNT含量的增加, 材料的室温电阻率增大, 同时陶瓷的电阻突跳比下降。     

Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3系无铅陶瓷的压电、铁电及热释电性能

使用传统的固相烧结法制备了(1-x)Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3无铅压电陶瓷,研究了BaTiO3对陶瓷介电﹑压电﹑铁电及热释电性能的影响。X射线衍射仪(XRD)及扫描电子显微镜(SEM)分析表明,适量的BaTiO3能完全固溶到Bi0.5Na0.5TiO3陶瓷中,当BaTiO3含量为0.05x0.09时,(1-x)Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3陶瓷处于三方四方两相共存状态,形成了准同型相界(MPB)。在MPB处,陶瓷的介电﹑压电、铁电及热释电性能均达到最佳:d33～170pC/N,εr～869,kp～27%,Pr～32.91μC·cm-2,Ec～26.5kV·cm-1,p～2.01×10-8Ccm-2·℃-1,FV～1.81×10-2 m2·C-1,FD～0.82×10-5Pa-1/2。对阻抗频率特性的研究发现,BaTiO3的加入能使材料性能"软化"。研究还发现适量BaTiO3的加入能促使BNT压电陶瓷的退极化温度向高温方向移动,93Bi0.5Na0.5TiO3-7BaTiO3陶瓷在80℃开始由铁电相向反铁电相转变。     

球型Li_2Fe_(0.5)Mn_(0.5-x)V_xSiO_4(x=0-0.1)材料的合成及其电化学性能研究

采用一种简单的喷雾溅射法成功制备出了球型Li_2Fe_(0.5-x)Mn_0.5V_xSiO_4(x=0-0.1)。合成的产物经XRD和SEM分析手段进行表征。此外,还考察了V掺杂量对其电化学性能的影响,结果表明V掺杂量为0.05时能大幅度改善材料的电化学性能。     

(Bi0.5Na0.5)TiO3(BNT)基无铅压电陶瓷研究进展

(Bi0.5Na0.5)TiO3(BNT)基无铅压电陶瓷体系是目前研究最广泛的功能陶瓷材料之一.综述了BNT基无铅压电陶瓷的研究现状,讨论了相关体系的设计方法、铁电性、压电性以及BNT体系的制备方法.分析比较了BNT系压电陶瓷与Pb(Zr,Ti)O3(PZT)压电陶瓷的性能差异以及存在的问题,对BNT基无铅压电陶瓷进行了展望.     

Magnetoelectric and dielectric properties of Ni0.5Cu0.5Fe2O4–Ba0.5Pb0.5Ti0.5Zr0.5O3 ME composites

The (x) Ni_0.5Cu_0.5Fe₂O₄ + (1−x) Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ ME composites have been synthesized by a standard ceramic method. The presence of single phase in x = 0 and x = 1 as well as two phases in x = 0.15, 0.30 and 0.45 composites has been confirmed by XRD. The dielectric constant (ε′) and dielectric loss (tan δ) have been studied as a function of temperature and frequency. These composite materials exhibit maximum dielectric constant with a variation of frequency and temperature. The composite 15% Ni_0.5Cu_0.5Fe₂O₄ + 85% Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ had the highest magnetoelectric voltage coefficient of 0.248 mV/cm Oe at room temperature among the studied composites.     

Exchange biasing of magnetoelectric composites

Magnetoelectric composite materials are promising candidates for highly sensitive magnetic-field sensors. However, the composites showing the highest reported magnetoelectric coefficients require the presence of external d.c. magnetic bias fields, which is detrimental to their use as sensitive high-resolution magnetic-field sensors. Here, we report magnetoelectric composite materials that instead rely on intrinsic magnetic fields arising from exchange bias in the device. Thin-film magnetoelectric two-two composites were fabricated by magnetron sputtering on silicon-cantilever substrates. The composites consist of piezoelectric AlN and multilayers with the sequence Ta/Cu/Mn(70)Ir(30)/Fe(50)Co(50) or Ta/Cu/Mn(70)Ir(30)/Fe(70.2)Co(7.8)Si(12)B(10) serving as the magnetostrictive component. The thickness of the ferromagnetic layers and angle dependency of the exchange bias field are used to adjust the shift of the magnetostriction curve in such a way that the maximum piezomagnetic coefficient occurs at zero magnetic bias field. These self-biased composites show high sensitivity to a.c. magnetic fields with a maximum magnetoelectric coefficient of 96 V cm(-1) Oe(-1) at mechanical resonance.     

Magnetoelectric bending-mode structure based on Metglas/Pb(Zr,Ti)O₃ fiber laminates

A magnetoelectric (ME) bending-mode structure based on Metglas/Pb(Zr,Ti)O(3) fiber laminates has been studied. This bending mode had a fundamental resonance (FBR) of about 210 Hz, which was much lower than that of the longitudinal mode. Near the FBR, the ME voltage coefficient was about 400 V/cm·Oe. Magnetic sensors based on this bending mode had an equivalent magnetic noise floor of ≤ 0.3 pT/√Hz at f = 210 Hz.     

Effect of NiZnFeO4 content on PZT-pZN + NiZnFeO4 magnetoelectric composite

We fabricated and characterized the magnetoelectric (ME) properties of 3-0 ME composite materials comprised of the high piezoelectric voltage coefficient material, 0.9Pb(Zr0.52Ti0.48)O3-0.1 Pb(Zn1/3Nb2/3)O3 + 0.005Mn (PZT-PZN), and the magnetostrictive material, Ni0.8Zn0.2Fe2O4 (NZF). As the ME effect is generated by the product coupling between the piezoelectric properties and the magnetostrictive properties, the NZF content should be optimized for a higher ME coefficient. The dielectric constant and spontaneous polarization (P) were decreased with increasing NZF content before the percolation of the NZF particulates. However, as the NZF content exceeded the percolation content, the dielectric loss was dramatically increased due to the low resistivity of NZF. While the piezoelectric constant was decreased with increasing NZF content, the maximum magnetization was linearly increased. When we combined the piezoelectric and magnetostrictive effects, the ME composite sintered at 1200 degrees C with 20% NZF showed a maximum dE/dH of 27 mV/cm x Oe at a magnetic bias of 1240 Oe.     

Magnetic field-induced strain and magnetoelectric effects in sandwich composite of ferromagnetic shape memory Ni-Mn-Ga crystal and piezoelectric PVDF polymer

A sandwich composite consisting of one layer of ferromagnetic shape memory Ni-Mn-Ga crystal plate bonded between two layers of piezoelectric PVDF polymer film was fabricated, and its magnetic field-induced strain (MFIS) and magnetoelectric (ME) effects were investigated, together with a monolithic Ni-Mn-Ga crystal, as functions of magnetic fields and mechanical load. The load-free dc- and ac-MFISs were 0.35 and 0.05% in the composite, and 5.6 and 0.3% in the monolithic crystal, respectively. The relatively smaller load-free MFISs in the composite than the monolithic crystal resulted from the clamping of martensitic twin-boundary motion in the Ni-Mn-Ga plate by the PVDF films. The largest ME coefficient (α(E)) was 0.58 V/cm·Oe at a magnetic bias field (H(Bias)) of 8.35 kOe under load-free condition. The mechanism of the ME effect originated from the mechanically mediated MFIS effect in the Ni-Mn-Ga plate and piezoelectric effect in the PVDF films. The measured α(E)-H(Bias) responses under different loads showed good agreement with the model prediction.     

Magnetic and magnetocaloric properties of nanocrystalline Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) manganites

Structural, magnetic and magnetocaloric properties of sol-gel prepared, nanocrystalline oxides Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) (cubic, space group Fm3m) have been studied. From the X-ray data, the crystallite size of Pro.7Ca0.3Mn0.5Co0,503 and Pr0.7Sr0.3Mn0.5Co0.5O3 samples is found to be approximately 24 nm and approximately15 nm respectively. High resolution transmission electron microscopy image shows average particle size of approximately 34 nm and approximately 20 nm. Magnetization measurements indicate a Curie temperature of approximately 153 K and approximately172 K in applied magnetic field of 100 Oe for Pr0.7Ca0.3Mn0.5Co0.5O3 and Pr0.7Sr0.3Mn0.5Co0.O3 compounds. The magnetization versus applied magnetic field curves obtained at temperatures below 150 K show significant hysteresis and magnetization is not saturated even in a field of 7 T. The magnetocaloric effect is calculated from M versus H data obtained at various temperatures. Magnetic entropy change shows a maximum near T(c) for both the samples and is of the order approximately 2.5 J/kg/K.     

Enhanced electric field tunable magnetic properties of lead-free Na0.5Bi0.5TiO3–MnFe2O4 multiferroic composites

Strong magnetoelectric (ME) interaction was exhibited at both dc and microwave frequencies in a lead-free multiferroic particulate composites of Na_0.5Bi_0.5TiO₃ (NBT) and MnFe₂O₄ (MFO) multiferroic, which were prepared by sol–gel route. The room temperature permeability measurements were carried out in the frequency range of 1 MHz–1 GHz. A systematic study of structural, magnetic and ME properties were undertaken. The room temperature ferromagnetic resonance (FMR) was studied. Strong ME coupling is demonstrated in 70NBT–30MFO composite by an electrostatically tunable FMR field shift up to 428 Oe (at E = 4 kV/cm), which increases to a large value of 640 Oe at E = 8 kV/cm. Furthermore, these lead-free multiferroic composites exhibiting electrostatically induced magnetic resonance field at microwave frequencies provide great opportunities for electric field tunable microwave devices.     

Magnetoelectric effect of the multilayered CoFe2O4/BaTiO3 composites fabricated by tape casting

This paper presents the structural, ferroelectric, ferromagnetic, resonance and magnetoelectric (ME) properties of multilayered ME composites fabricated using tape casting method. The compositions corresponding to CoFe₂O₄ (CFO) with particle size of ~150?nm and BaTiO₃ (BTO) with particle size of ~100?nm were chosen as ferromagnetic and ferroelectric phases, respectively. Delamination was found at the interface between CFO and BTO layers, which was related to the residual stress due to the difference in thermal expansion coefficient between the two layers. The largest direct magnetoelectric and converse magnetoelectric coefficients of the multilayered ME composite were, respectively, 36?μV/cm?Oe at a bias magnetic field of 2,800?Oe and 1.16?×?10^?3?G/V at a frequency of 30?kHz. In addition, the corresponding interfacial coupling coefficient was calculated to be 3.2?×?10^?5. For the multilayered ME composite, a resonance frequency of 4.96?MHz and a bandwidth of 40?kHz were obtained using capacitance-frequency spectrum method.