Fe@SiO₂软磁复合材料的电子结构和磁性能

Fe@SiO 2 软磁复合材料的电子结构和磁性能 Electronic structure and magnetic properties of Fe@SiO 2 soft magnetic composites first-author corresp 陈仕奇，博士，副教授，从事粉末冶金材料研究；E-mail：929144802@qq.com 陈仕奇，博士，副教授，从事粉末冶金材料研究；E-mail：929144802@qq.com 929144802@qq.com 中南大学 粉末冶金研究院，湖南 长沙，410083 中南大学 粉末冶金研究院，湖南 长沙，410083 Powder Metallurgy Research Institute, Central South University, Changsha 410083, China Powder Metallurgy Research Institute, Central South University, Changsha 410083, China 杨幼平 用化学沉淀法和粉末冶金方法制备Fe@SiO 2 软磁复合材料，采用X射线衍射(XRD)、透射电镜(TEM)等方法和基于密度泛函理论(DFT)的第一性原理计算，研究材料的显微结构、电子结构和磁性能。研究结果表明：Fe@SiO 2 软磁复合材料的涡流损耗 P e 随SiO 2 包覆量的增加而大幅度减小，当正硅酸乙酯(TEOS)的添加量为2 mL时，总损耗 P s 为132.7 W/kg(20 mT和200 kHz时)，最大磁导率 μ m 为55，综合软磁性能最佳。Fe粉表面包覆着一层均匀、致密、完整的半透明SiO 2 包覆层，包覆层与Fe基体之间结合紧密。Fe/SiO 2 界面处Fe—O和Fe—Si共价键的形成使其具有良好的稳定性，其界面黏附功 W ad 约为1.18 J/m 2 。Fe—O共价键的形成归因于Fe 3d电子与O 2p电子在-4.7~-1.6 eV和-7.5~-6 eV的区间内的强杂化；Fe—Si共价键的形成主要归因于界面处Si 2s和Fe 3s电子在低能量区域-9.7~-8.8 eV杂化态的出现。该共价键的形成可有效束缚传导电子，提高表面电阻率，对降低Fe/SiO 2 软磁复合材料的损耗起着重要作用。 Fe@SiO 2 soft magnetic composites(SMCs) were prepared via a chemical precipitation method and powder metallurgy technique. Microstructure, electronic structure and magnetic properties were investigated by X-ray diffraction(XRD), transmission electron microscopy(TEM) and first-principles calculation based on density functional theory(DFT). The results show that the eddy current loss P e of Fe@SiO 2 SMCs substantially reduces with the increase of SiO 2 coating content. The sample coated with 2 mL ethyl orthosilicate(TEOS) exhibits the best comprehensive magnetic properties with total loss P s of 132.7 W/kg and the maximum magnetic permeability μ m of 55 (20 mT and 200 kHz). The semi-transparent SiO 2 coating layer has a uniform, dense, and compact morphology, indicating good adhesion between the SiO 2 and the Fe matrix. The Fe/SiO 2 interface has good structural stability with an adhesion work ( W ad ) of about 1.18 J/m 2 , ascribed to the formation of Fe—O and Fe—Si covalent bonds. The strong hybridization between Fe 3d electrons and O 2p electrons in the range of -4.7 to -1.6 eV and -7.5 to -6.0 eV demonstrates the existence of Fe—O covalent bond. The formation of Fe—Si covalent bond is mainly attributed to the appearance of Si 2s and Fe 3s hybrid states in the low energy region of -9.7 to -8.8 eV. Fe—O and Fe—Si covalent bond can also effectively bind conduction electrons and increase the surface resistivity, which plays an important role in reducing the loss of Fe/SiO 2 SMCs. Fe@SiO 2 磁性能 第一性原理 界面结构 键合特性 Fe@SiO 2 magnetic properties first principles interface structure bonding properties http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681111&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681113&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681112&type= 14.95016479 14.95016479 近年来，5G通讯、风力发电、光伏发电的发展对电子元器件的高频化和小型化提出了新的需求。软磁复合材料(SMCs)在高频下具有磁导率高、涡流损耗低的特性，受到了广泛关注 [ 1 1 - 3 3 1-3 ] 。SMCs的制备工艺过程包括粉末绝缘包覆、压制、热处理等，其中绝缘包覆是提高高频磁性能的关键 [ 4 4 - 5 5 4-5 ] 。 SMCs常用的绝缘包覆剂包括有机类包覆剂和无机类包覆剂。前者包括环氧树脂、硅树脂、聚酰亚胺、丙烯酸等有机高分子聚合物 [ 6 6 - 7 7 6-7 ] ；后者主要为氧化物、金属磷酸盐、硫化物和氮化物等，具有热稳定性好、电阻率高的特点，有利于提高SMCs的综合磁性能 [ 8 8 - 11 11 8-11 ] 。目前研究较多的Fe/氧化物SMCs包括Fe/SiO 2 、Fe/Al 2 O 3 、Fe/MgO、Fe/Fe 2 O 3 、Fe/ZrO 2 等 [ 12 12 - 16 16 12-16 ] 。例如，CHOI等 [ 17 17 ] 制备了Fe/Al 2 O 3 SMCs，其磁导率和损耗分别为12.1和49.3 W/kg (50 mT和100 kHz时)；LI等 [ 18 18 ] 制备了Fe/ZrO 2 SMCs，其磁导率和损耗分别为83和255.2 W/kg (20 mT和100 kHz时)；WU等 [ 6 6 ] 制备了Fe/SiO 2 SMCs，其磁导率和损耗分别为60.6和148.5 W/kg (50 mT和100 kHz时)。一般认为，Fe/SiO 2 SMCs的优良高频软磁性能主要来源于由Si—O共价键连接而成的三维网络状SiO 2 绝缘包覆层，其电阻率可达6.0×10 12 μΩ·m [ 19 19 ] 。SiO 2 作为绝缘包覆剂的SMCs体系还包括FeSi/SiO 2 、FeSiCr/SiO 2 、FeSiAl/SiO 2 等 [ 20 20 - 22 22 20-22 ] ，其在高频下都具有磁导率高和损耗低的优点。例如，LUO等 [ 23 23 ] 制备的FeSi/SiO 2 SMCs的磁导率和损耗分别为38和48.9 W/kg(50 mT和50 kHz时)；任劲松等 [ 24 24 ] 制备的FeSiCr/SiO 2 的磁导率和损耗分别为63和98.6 W/kg (50 mT和100 kHz时)。FAN等 [ 22 22 ] 制备的FeSiAl/SiO 2 的磁导率和损耗分别为90和480.3 W/kg (50 mT和50 kHz时)。 尽管目前SiO 2 等氧化物已被广泛用作SMCs的绝缘包覆层，但大都限于实验研究，对于氧化物与磁性基体界面之间的界面稳定性、键合特性和电子结构等方面的研究还鲜有报道。金属/氧化物作为一种异质界面，界面之间的结合能力决定了复合材料的包覆效果和性能稳定性；界面之间的键合特性和电子结构可反映其绝缘性能 [ 25 25 ] 。因此，研究SMCs基体与包覆层的界面性质对制备高性能SMCs来说是至关重要的。近年来，第一性原理模拟计算方法被应用于金属-陶瓷界面研究，如Cu/ α-Al 2 O 3 [ 26 26 ] 、Fe 3 Si@SiO 2 [ 27 27 ] 吸波材料。基于此，本文作者通过化学沉淀法制备Fe@SiO 2 SMCs并研究其频率特性，采用密度泛函理论(DFT)的 VASP(vienna ab-into simulation package，VASP)软件包，对Fe(110)/SiO 2 的界面黏附功、键合特性和电子结构进行计算，分析Fe/SiO 2 界面性质对Fe@SiO 2 SMCs性能的影响，为制备高性能SMCs提供新理论基础和研究思路。 1 实验和计算方法 1 1.1 　 Fe@SiO 2 复合材料的制备 2 将20 g Fe粉加入到装有200 mL丙酮的三口烧瓶中，机械搅拌10 min，缓慢滴入1 mL表面改性剂KH550和5 mL去离子水，搅拌60 min。继续滴加3 mL氨水调节溶液pH至9~10时添加TEOS(C 8 H 20 O 4 Si)，控制溶液温度为50 ℃并搅拌5 h。最后，用丙酮将粉末清洗3次，并在65 ℃干燥6 h，获得Fe@SiO 2 复合粉末。实验中，TEOS的加入量分别为1、2、3和4 mL，分别对应于4个Fe@SiO 2 软磁复合粉末样品CS-1、CS-2、CS-3和CS-4。 将Fe@SiO 2 复合粉末与质量分数为0.3%的硬脂酸锌混合，然后在1 400 MPa的压制压力下压制成外径为19 mm、内径为13 mm的环形试样。最后将压坯在管式炉中于高纯氩气气氛保护下在500 ℃保温1 h，制备出Fe@SiO 2 软磁复合材料。 1.2 　样品表征 2 相结构由D/max 2550 X射线衍射仪测量，采用Cu靶Kα线辐射，扫描范围选取2 θ 为20°~90°，其加速电压为40 kV，电流强度为250 mA。显微结构和能谱分析(EDAX)由JEOL公司的JSM-6300LV型扫描电子显微镜、FEI公司的TALOS F200X型透射电子显微镜和配套的X射线能谱仪来进行观测和表征。粉末表面官能团采用Thermo Fisher Scientific公司的Nicolet 6700型傅里叶变换红外光谱仪测量。粉末磁化强度 M 随外场磁场强度 H 的变化曲线( M - H 曲线)由Lake Shore 7410型振动样品磁强计在室温下测出。直流磁性能由MATS-2010型软磁直流测试仪测量，交流磁性能测试设备为TD8130型交流磁性能测试仪，有效磁导率和品质因数由TH2826型LCR数字电桥测得。 1.3 　计算方法 2 本文基于密度泛函理论(DFT)的VASP程序包进行计算，且所有计算均采用广义梯度近似(GGA-PBE)和平面波超软赝势。α-Fe为BCC结构，非晶SiO 2 的结构模型见文献[ 28 28 ]。α-Fe、SiO 2 和α-Fe/SiO 2 界面模型的 k 点网格分别为3×3×3、3×3×3和3×3×1。平面波的截断能取500 eV，电子自洽和离子弛豫的收敛标准分别为10 -7 eV和0.05 eV/nm。 2 实验结果与讨论 1 2.1 　 Fe@SiO 2 复合粉末的表征及磁性能 2 图1 图1 (a)所示为Fe@SiO 2 复合粉末的XRD图。由 图1 图1 (a)可见：Fe@SiO 2 复合粉末的相结构均为 <math id="M1"><mi mathvariant="normal">α</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680901&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680898&type= 1.94733346 2.62466669 -Fe主相(JCPDS No. 06-0696)，但在2 θ 为20°~25°之间出现了非晶态SiO 2 所对应的漫散射峰，其强度随着TEOS添加量的增加而增强，表明非晶SiO 2 的包覆量逐渐增多。同时在35°左右出现了微弱的Fe 2 O 3 衍射峰，应是Fe粉在包覆过程中微量氧化所致。 图1 图1 (b)所示为Fe@SiO 2 复合粉末的 M - H 曲线。TEOS的添加量 x 分别为0、1、2、3和4 mL时，复合粉末的饱和磁化强度 M s 分别为210.2、209.1、206.4、198.0和191.9 A·m 2 /kg，表明微量SiO 2 非磁性绝缘层( x ≤2 mL)对复合粉末的 M s 降低较少。 (a) 纯Fe和Fe@SiO 2 复合粉末的XRD图；(b) M - H 曲线 图2 图2 所示为Fe@SiO 2 复合粉末样品CS-1的SEM图。由 图2 图2 (a)可见：原始Fe粉表面光滑，平均粒径为2~5 μm，粉末颗粒之间稍有团聚。Fe@SiO 2 复合粉末表面粗糙，沉积了纳米级包覆层，具有良好的分散性( 图2 图2 (b)和(c))。从 图2 图2 (d)可见：包覆后的Fe粉表面含有O和Si元素。 图3 图3 所示为Fe@SiO 2 复合粉末样品CS-1的红外光谱分析。由 图3 图3 可见：包覆之后的粉末在482 cm -1 (Si—O—Si键的弯曲振动峰)和1 107 cm -1 (Si—O—Si键的非对称振动峰)出现了明显的SiO 2 标志性吸收峰，证明SiO 2 被包覆于Fe粉表面。 (a) 原始Fe粉的SEM图；(b) CS-1的SEM图(低倍)；(c) CS-1的SEM图(高倍)；(d) CS-1的EDAX图 图4 图4 所示为CS-1和CS-4的TEM图。由 图4 图4 可见：Fe粉表面包覆着一层均匀、致密、完整的半透明SiO 2 包覆层。当TEOS添加量较少(1 mL)时( 图4 图4 (a))，SiO 2 包覆层的厚度较小，约为10 nm。当TEOS添加量增加到4 mL时( 图4 图4 (b))，SiO 2 包覆层的厚度显著增加，最厚处可达50~150 nm。从 图4 图4 (c)可见：SiO 2 包覆层无明显的晶格衍衬像，为典型的非晶结构；包覆层与Fe基体之间结合紧密、无孔洞，说明Fe与SiO 2 的界面结合能力较强。 (a) CS-1的TEM形貌图；(b) CS-4的TEM形貌图；(c) CS-4的TEM衍射图 2.2 　 Fe/SiO 2 的界面电子结构 2 首先对Fe/SiO 2 界面原子的结合特性进行测试，发现Fe(110)晶面与非晶SiO 2 中的O终端侨联时，体系最稳定，这一结果与Fe/Al 2 O 3 计算的一致 [ 29 29 ] 。 图5 图5 所示为Fe(110)与非晶SiO 2 中的O终端侨联构建的Fe/SiO 2 界面超胞模型，其中，非晶SiO 2 的结构模型见文献[ 28 28 ]。经收敛性测试，选取Fe(110)原子层为5层，真空层的厚度为1.6 nm。 界面原子的结合强度由黏附功 W ad 来评价。 W ad 为将界面分成2个自由表面所需的可逆功， W ad 越大，界面间原子结合越紧密，其计算公式为 [ 30 30 ] <math display="block" id="M2"><msub><mrow><mi>W</mi></mrow><mrow><mi mathvariant="normal">a</mi><mi mathvariant="normal">d</mi></mrow></msub><mo>=</mo><mfenced separators="|"><mrow><msubsup><mrow><mi>E</mi></mrow><mrow><mi mathvariant="normal">F</mi><mi mathvariant="normal">e</mi></mrow><mrow><mi 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mathvariant="normal">l</mi></mrow></msubsup></mrow></mfenced><mo>/</mo><mi>A</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680940&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680945&type= 45.72000122 6.01133299 其中： <math id="M3"><msubsup><mrow><mi>E</mi></mrow><mrow><mi mathvariant="normal">F</mi><mi mathvariant="normal">e</mi></mrow><mrow><mi mathvariant="normal">s</mi><mi mathvariant="normal">l</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">b</mi></mrow></msubsup></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680958&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680947&type= 6.34999990 4.06400013 和 <math id="M4"><msubsup><mrow><mi>E</mi></mrow><mrow><mi mathvariant="normal">S</mi><mi mathvariant="normal">i</mi><msub><mrow><mi mathvariant="normal">O</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msub></mrow><mrow><mi 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http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680955&type= 9.73666668 4.65666676 为Fe/SiO 2 界面结构的总能； A 为界面面积。经测试，初始界面间距 d 取0.17 nm，对应的 W ad 有最大值，为1.18 J/m 2 。 界面结合强度取决于界面处原子的电子结构与成键状态。 图6 图6 所示为Fe/SiO 2 界面处(010)截面的差分电荷密度图。从 图6 图6 可见：界面原子的电荷进行了再分布。首先，Fe与O原子间存在强的电荷聚集区(红色虚框)，表明Fe—O共价键的形成；其次，Fe与Si原子间也存在弱的电荷聚集区(蓝色虚框)，并且电荷中心更靠近Fe，说明形成了具有离子键特性的弱Fe—Si共价键。Fe与O之间的强共价键和Fe与Si之间具有共价键和离子键特性的化学键都会提高Fe/SiO 2 界面结合强度。 图7 图7 所示为Fe/SiO 2 界面处Fe原子与其近邻O、Si原子的分态密度(PDOS)。从 图7 图7 (a)可见：界面处Fe 3d电子与O 2p电子在-4.7~-1.6 eV和-7.5~-6.0 eV的区间内存在强的杂化现象；从 图7 图7 (b)可见：与Si近邻的Fe原子在低能量区域-9.7~-8.8 eV出现新态，该新态主要由Si 2s电子和Fe 3s电子贡献，标志着Fe—Si共价键的存在。可见，Fe/SiO 2 的界面稳定性来源于Fe—O和Fe—Si共价键的形成。该共价键还可有效束缚传导电子，提高表面Fe原子的电阻率，进而降低材料的涡流损耗。 (a) Fe/SiO 2 界面处Fe原子与其近邻O原子的分态密度(PDOS)； (b) Fe/SiO 2 界面处Fe原子与其近邻Si原子的分态密度(PDOS) 2.3 　 Fe@SiO 2 软磁复合材料的交流磁性能 2 图8 图8 所示为Fe@SiO 2 SMCs的磁导率 <math id="M6"><msub><mrow><mi>μ</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680987&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680985&type= 3.21733332 4.48733330 和品质因数 <math id="M7"><mi>Q</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680992&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680990&type= 2.70933342 3.38666677 随频率 <math id="M8"><mi>f</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681006&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43680993&type= 2.37066650 3.38666677 的变化曲线。由 图8 图8 (a)可见：当TEOS添加量 x ≥2 mL时，Fe@SiO 2 具有良好的频率稳定性，截止频率可达5 MHz以上； Q 及其对应的频率均随 x 的增加而增大，当 x 为2~4 mL时， Q 为36~66。可见，当TEOS添加量 x ≥2 mL时，Fe@SiO 2 的高频应用特性优良。 (a) 不同TEOS添加量的Fe@SiO 2 软磁复合材料的 <math id="M11"><msub><mrow><mi>μ</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681000&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681018&type= 3.04800010 4.06400013 随 f 变化曲线； (b) 不同TEOS添加量的Fe@SiO 2 软磁复合材料的 Q 随 f 变化曲线 软磁复合材料在交流磁化过程中的总铁芯损耗 P s 主要包括磁滞损耗 <math id="M12"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">h</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681028&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681026&type= 3.64066648 3.72533321 和涡流损耗 <math id="M13"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681032&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681030&type= 3.55599999 3.72533321 ，计算公式如下 [ 31 31 - 32 32 31-32 ] ： <math display="block" id="M14"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub><mo>=</mo><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">h</mi></mrow></msub><mo>+</mo><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub><mo>=</mo><msub><mrow><mi>K</mi></mrow><mrow><mi mathvariant="normal">h</mi></mrow></msub><mi>f</mi><mo>+</mo><msub><mrow><mi>K</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub><msup><mrow><mi>f</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msup></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681051&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681049&type= 36.99933624 4.82600021 <math display="block" id="M15"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">h</mi></mrow></msub><mo>=</mo><mi>f</mi><mo>∮</mo><mi>H</mi><mi mathvariant="normal">d</mi><mi>B</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681054&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681053&type= 18.79599953 6.43466663 <math display="block" id="M16"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub><mo>=</mo><mfrac><mrow><mi>C</mi><msup><mrow><mi>B</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msup><msup><mrow><mi>f</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msup><msup><mrow><mi>d</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msup></mrow><mrow><mi>ρ</mi></mrow></mfrac></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681057&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681055&type= 22.01333237 8.55133343 其中： f 为频率； H 为磁场强度； B 为磁感应强度； d 为试样厚度； <math id="M17"><mi>ρ</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681061&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681059&type= 2.03200006 3.38666677 为电阻率； <math id="M18"><mi>C</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681036&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681034&type= 2.62466669 2.62466669 、 <math id="M19"><msub><mrow><mi>K</mi></mrow><mrow><mi mathvariant="normal">h</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681041&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681039&type= 3.89466691 3.72533321 和 <math id="M20"><msub><mrow><mi>K</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681043&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681068&type= 3.72533321 3.72533321 为比例常数。由式( 2 2 )~( 4 4 )可知： <math id="M21"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub><mo>∝</mo><msup><mrow><mi>f</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msup></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681046&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681044&type= 10.49866676 4.82600021 ，高频下的总损耗主要为涡流损耗；提高材料的电阻率有助于降低材料的 <math id="M22"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681079&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681078&type= 3.55599999 3.72533321 ，从而降低 <math id="M23"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681081&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681080&type= 3.38666677 3.72533321 。 图9 图9 (a)和(b)所示分别为Fe@SiO 2 SMCs的最大磁导率 μ m 和总损耗 P s 随频率 f 和TEOS添加量 x 的变化曲线(测试条件为 B =20 mT和 f =10～200 kHz)。由 图9 图9 (a)可见：虽然 μ m 随着 x 的增加而单调减小，由 f =10 kHz和 x =1 mL时的61降低到 f =10 kHz和 x =4 mL时的29，但其频率稳定性更优。由 图9 图9 (b)可见：Fe@SiO 2 SMCs的 P s 随着 f 的增加而快速上升，且随 x 的增加而大幅单调减小，在20 mT和100 kHz的条件下测试时， P s 从Fe的207.1 W/kg降到CS-4的15.6 W/kg。利用 式(4) 式(4) 将 P s 分离出磁滞损耗 <math id="M24"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">h</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681076&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681088&type= 3.64066648 3.72533321 和涡流损耗 <math id="M25"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681086&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681084&type= 3.55599999 3.72533321 (见 图9 图9 (c)和(d))。由 图9 图9 (c)可见： <math id="M26"><msub><mrow><mi>P</mi></mrow><mrow><mi mathvariant="normal">h</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681076&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681088&type= 3.64066648 3.72533321 随着 x 增加而小幅增大，主要是包覆后样品的矫顽力增加所致。从 图9 图9 (d)可见： P e 随着 x 增加而显著减小；在不同频率下 P s 远高于 P e ，表明材料的 P s 主要由 P e 贡献。当TEOS的添加量为2 mL时，材料具有最佳的综合磁性能， P s 为132.7 W/kg (20 mT和200 kHz时)， μ m 为55。测试表明，材料包覆SiO 2 后的电阻率远比包覆前的大，且随着TEOS添加量的增加而提高，当 x 分别为0、1、2、3和4 mL时，电阻率分别为0.2、275.6、335.4、371.3和389.6 μΩ·m。可见，SiO 2 绝缘层可有效增加Fe@SiO 2 SMCs的电阻率，降低涡流损耗。计算表明，Fe/SiO 2 界面处强的Fe—O和Fe—Si共价键的形成，一方面可以提高界面的结合强度，同时还可有效束缚传导电子，从而提高表面Fe原子的电阻率，对于降低Fe/SiO 2 软磁复合材料的损耗起着重要作用。 (a) μ m ；(b) P s ；(c) P h ；(d) P e 3 结论 1 1) 当TEOS添加量 x ≥2 mL时，Fe@SiO 2 SMCs材料具有良好的频率稳定性、较高的 Q 、低的 P e 和 P s ，但 μ m 和 M s 随 x 的增加而降低。当 x =2 mL时，材料的 P s 为132.7 W/kg (20 mT和200 kHz时)， <math id="M27"><msub><mrow><mi>μ</mi></mrow><mrow><mi mathvariant="normal">m</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681110&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=43681109&type= 3.97933316 4.48733330 为55，具有最佳的综合磁性能。 2) Fe粉表面包覆着一层均匀、致密的半透明非晶SiO 2 绝缘层。当TEOS添加量由1 mL增加到 4 mL时，SiO 2 绝缘层的厚度由10 nm增加到50~150 nm。 3) Fe—O和Fe—Si共价键的形成使Fe/SiO 2 界面具有良好的结构稳定性，界面黏附功 W ad 约为1.18 J/m 2 。Fe—O共价键的形成归因于Fe 3d电子与O 2p电子在-4.7～-1.6 eV和-7.5～-6 eV的区间内的强杂化；Fe—Si共价键的形成来源于Si 2s和Fe 3s电子在-9.7～-8.8 eV杂化态的出现。该共价键还可有效束缚传导电子，提高表面Fe原子的电阻率，进而降低材料的涡流损耗。 参考文献 黄伯云 , 韦伟峰 , 李松林 , 等 . 现代粉末冶金材料与技术进展 [J]. 中国有色金属学报 , 2019 , 29 ( 9 ): 1917 - 1933 . 现代粉末冶金材料与技术进展 HUANG Baiyun , WEI Weifeng , LI Songlin , et al . 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Electronic structure and magnetic properties of Fe@SiO2 soft magnetic composites[J]. Journal of Central South University(Science and Technology), 2023, 54(4): 1272-1280. 国家自然科学基金资助项目(51574293)；湖南省自然科学基金资助项目(2020JJ4713) Project (51574293) supported by the National Natural Science Foundation of China; Project(2020JJ4713) supported by the Natural Science Foundation of Hunan Province 2022-06-14 2022-08-11 2023-04-26 2023-05-22 37692169 中南大学学报(自然科学版) 4 54