ZnO陶瓷及其应用

1、2021-7-101ZnO陶瓷及应用第四组 材料1301班压敏陶瓷介绍2021-7-10ZnO陶瓷及应用2压敏陶瓷或称压敏变阻器，指对电压变化敏感的非线性电阻陶瓷（即电阻值与外加电压成显著的非线性关系），其伏安特性曲线如图如图。当电压低于某一临界值时，压敏陶瓷的阻值非常高，几乎为一绝缘体，当电压超过这一临界值时，电阻值急剧减小，接近于导体。2021-7-10ZnO陶瓷及应用3从1931年日本将SiC用来吸收雷击突波以来，已经出现了多种压敏陶瓷电阻器的应用，如有线电话交换机用它消除电火花、硅整流器、彩色电视机用它吸收异常电压、微型电动机用它来吸收噪声及对电机进行过压保护和继电保护等制造压敏半导体

2、 陶瓷材料有SiC、ZnO、BaTiO3、Fe2O3、SnO2、SrTiO3等。其中BaTiO3、Fe2O3利用的是电极与烧结体界面的非欧姆型，而SiC、ZnO、SrTiO3利用的是晶界非欧姆特性。目前应用最广、性能最好的是ZnO压敏半导体陶瓷。2021-7-10ZnO陶瓷及应用4各种变阻器特性比较可见ZnO远优于其他材料ZnO简介2021-7-10ZnO陶瓷及应用5历史起源结构性能制备应用：（压敏陶瓷、掺杂半导体）前景历史起源2021-7-106ZnO陶瓷及应用人类很早便学会了使用氧化锌作涂料或外用医药，但是人类发现氧化锌的历史难以追溯。氧化锌在古代和近代的另一主要用途是涂料，称为锌白。在2

3、0世纪后半叶，氧化锌多用在了橡胶工业。在20世纪70年代，氧化锌的第二大用途是是复印纸添加剂。现在，晶粒微小的氧化锌开始在纳米材料领域扩展应用范围结构结构ZnO的晶体结构纤锌矿晶体结构，其中氧离子以六方密堆积排列，锌离子占据了一半四面体间隙。也有立方闪锌矿结构，以及比较罕见的氯化钠式八面体结构纤锌矿结构在三者中稳定性最高，最常见2021-7-107ZnO陶瓷及应用O2-Zn2+结构结构2021-7-10ZnO陶瓷及应用8ZnO的能带结构ZnO的能带由O2-满的2p能级和Zn2+空的4s能级所组成的。当离子相互靠近而形成晶体时，这些能级就形成能带。满的2p和空的4s之间的禁带宽度约为3.23.4

4、 eV。从禁带宽度看，室温下ZnO应是一绝缘体。 （禁带宽度是指一个带隙宽度(单位是电子伏特（eV)，固体中电子的能量是不可以连续取值的，而是一些不连续的能带，要导电就要有自由电子存在，自由电子存在的能带称为导带（能导电），被束缚的电子要成为自由电子，就必须获得足够能量从价带跃迁到导带，这个能量的最小值就是禁带宽度。绝缘体的禁带宽度一般很宽， 约为3 6eV，半导体的禁带宽度较窄，约为 0.1 2eV。）半导体化ZnO的半导体化有三种情况。1.由于本证缺陷。ZnO晶格结构间隙大，晶格中的Zn很容易脱离原来的位置进入间隙位置，形成Zn空位。 2021-7-109ZnO陶瓷及应用2021-7-10

5、ZnO陶瓷及应用102.强制还原。在高温低氧分压下ZnO发生分解。分解可以形成间隙Zn离子，也可以形成氧空位。半导体化半导体化2021-7-10ZnO陶瓷及应用113.掺杂。若引入高价阳离子，如Al3+，Cr3+，Ga3+，In3+等，这些阳离子在ZnO中形成施主中心。若掺入低价金属离子，如Li+，Cu+，Ag+等，在氧化气氛，Li+置换Zn2+形成受主电导。这种掺杂与气氛有关，如果在还原气氛中，Li2O的掺杂也可以形成施主电导。ZnO压敏瓷的制备2021-7-10ZnO陶瓷及应用12ZnO压敏陶瓷通常是在ZnO中加入Bi、Mn、Co、Ba、Pb、Sb、Cr、Si等金属氧化物，按典型粉末工艺制

6、造，烧结后进行涂Ag等工序。主要的制备方法为掺杂。掺杂可用机械混合的方法，也可用化学方法。同时掺杂制ZnO半导体还可以制造有关热电材料的半导体。ZnO压敏电阻的主要电参数2021-7-10ZnO陶瓷及应用13ZnO压敏电阻的主要电参数2021-7-10ZnO陶瓷及应用14非线性系数图中在大于Jb的某一电流范围内，J和E的对数之间近似于直线关系。用方程lgJ=lgE-A表示，另A=lgC，这J=（E/C）（J为电流密度，E为电场强度，C为常数）为直线的斜率，越大，直线越陡，电阻的非线性特性越强，因此将成为“非线性系数”。ZnO压敏电阻器I-V曲线ZnO压敏电阻的主要电参数2021-7-10ZnO

7、陶瓷及应用15一般来说在一定几何形状下，电流在1mA附近的的值最大，因此常取与1mA电流对应的电压为“压敏电压”，记为V1mA。此外，非线性系数还和温度有关。（77K相较298K的峰值升高且提前。）值与电流的关系ZnO压敏电阻的主要电参数2021-7-10ZnO陶瓷及应用16C值（对照与电阻）定义：当变阻器上流过1mA/cm2电流时，在每毫米上的电压降为该压敏电阻的C值在一定时，C越大，一定电流下所对应的电压值越高，因此常称为“非线性电阻”又因为它取决于材料的成分。结构和制造工艺，所以又常称为“材料常数”ZnO压敏电阻的主要电参数2021-7-10ZnO陶瓷及应用17漏电流压敏电阻正常工作时流

8、过的电流叫“漏电流”，与与电压和温度有关。要使压敏电阻器正常可靠地工作，漏电电流必须尽可能小。一般来说可控制在50微安到100微安之间。在选择压敏电阻的工作电压时，必须根据允许的漏电流值。ZnO压敏电阻的主要电参数2021-7-10ZnO陶瓷及应用18电压温度系数定义：在规定温度范围内，温度每变化一度，零功率条件下测得的压敏电压的相对变化率叫压敏电压的温度系数。用来描述压敏电阻随着温度的上升，压敏电压下降的变化关系。ZnO压敏电阻的主要电参数2021-7-10ZnO陶瓷及应用19流通容量（或称流通能力或通流量）。压敏电阻经过持续交、直流负载和高浪涌电流（浪涌电流指电源接通瞬间，流入电源设备的峰

9、值电流。由于输入滤波电容迅速充电，所以该峰值电流远远大于稳态输入电流）的冲击后， I-V特性会发生蜕变现象。这种蜕变，也称压敏电阻的老化。对于实际应用来说这种老化是不允许的。因此必须对经高浪涌电流冲击后的V1mA下降有所限制，并把下降多少作为衡量压敏电阻承受高浪涌电流冲击能力的尺度。把满足V1mA下降要求的压敏电阻所能承受的某一波形的最大冲击电流叫做压敏电阻器的“通流容量”。通流容量一方面给取决于冲击电流的峰值，一方面取决于冲击电流的持续时间，即取决于消耗的能量。ZnO压敏电阻的主要电参数2021-7-10ZnO陶瓷及应用20ZnO和SiC两种变阻器的特性比较。ZnO和SiC变阻器的特性压敏变

10、阻器的应用2021-7-10ZnO陶瓷及应用21压敏变阻器广泛地用作过压保护，高能流涌吸收，高压稳压等方面。 举例1、过压保护正常工作时，压敏电阻两端电压较小，压敏电阻阻值较大，所产生的漏流很小。压敏电阻l 异常情况发生时2021-7-10ZnO陶瓷及应用22举例2 、稳压方面由于压敏变阻器有高的非线性I-V特性，所以负载两端电压的少许变化就会使流经压敏变阻器的电流Iv产生很大的变化，从而使电压增量几乎全在R0，上的压降所补偿。（猜测：稳压应用的应该始终处于击穿状态）压敏变阻器稳压线路原理图压敏变阻器的应用2021-7-10ZnO陶瓷及应用23ZnO前景展望ZnO前景展望2021-7-10Zn

11、O陶瓷及应用24在一篇研究生论文中发现这个例子ZnO前景展望2021-7-10ZnO陶瓷及应用25最近发展了以某些过渡族元素氧化物和稀土氧化物为主要添加剂的氧化锌压敏电阻器。表现出能量吸收容量大，在大电流时的非线性好，响应时间快，寿命长击穿电压大于200V/mm等特性。适用于做高压电站的浪涌放电器。可见氧化锌压敏陶瓷的应用还是十分广阔的ZnO热电材料2021-7-10ZnO陶瓷及应用26应用背景能源短缺与生态、环护问题越来越深刻影响着人类的生活与发展推动了热电材料的研究。2021-7-10ZnO陶瓷及应用27应用背景2021-7-10ZnO陶瓷及应用28应用背景能源短缺与生态、环护问题越来越深

12、刻影响着人类的生活与发展推动了热电材料的研究。应用应用背景背景2021-7-10ZnO陶瓷及应用292021-7-10ZnO陶瓷及应用30上海超算中心系统设备用电参数超算计算机系统的60%以热能损耗制冷系统占供电系统的用能为37%成为回收的最佳材料1.1. 什么是热电材料什么是热电材料 热电材料（也称温差电材料，thermoelectric materials）是一种利用固体内部载流子运动，实现热能和电能直接相互转换的功能材料。 什么是热电效应什么是热电效应 热电效应是电流引起的可逆热效应和温差引起的电效应的总称，包括Seebeck效应、Peltier效应和Thomson效应。2021-7-1

13、031ZnO陶瓷及应用热电材料热电材料2021-7-1032Seebeck效应效应Peltier效应效应ZnO陶瓷及应用热电器件的工作原理热电器件的工作原理2021-7-10ZnO陶瓷及应用33热电制冷热电发电电子器件散热以及的几乎没有，这方面的学术研究很少。热电材料主要应用热电材料主要应用2021-7-1034ZnO陶瓷及应用热电性能评价热电性能评价2021-7-1035热电热电材料优点材料优点无运动部件、无噪声无运动部件、无噪声易于控制、可靠性高易于控制、可靠性高容易微型化容易微型化寿命长、无污染寿命长、无污染ZnO陶瓷及应用热电材料优点热电材料优点如何提高如何提高ZT值值2021-7-1

14、0ZnO陶瓷及应用36目前，通过相关文献的查阅：目前，通过相关文献的查阅： ZT值值由由量子限制效应得到显着提升（量子限制效应得到显着提升（ Bi Bi2 2TeTe3 3超晶格量子超晶格量子限制限制）；）； 多层的多层的BiBi2 2TeTe3 3/ Sb/ Sb2 2TeTe3 3和和AgPbSbTeAgPbSbTe纳米结构纳米结构合金都合金都表现出了非表现出了非凡的凡的性能，性能，ZTZT值超过了值超过了1.5(650K1.5(650K) )。 在在改进改进ZTZT的道路上，有人认为可以通过引入纳米级的的道路上，有人认为可以通过引入纳米级的成分成分，使使其带来量子限制效果，以提高功率因数

15、其带来量子限制效果，以提高功率因数S S2 2 ；有人认为可以在；有人认为可以在纳米结构内部设计较多界面以用来使热导率比电导率减小得更快，纳米结构内部设计较多界面以用来使热导率比电导率减小得更快，从而达到提高从而达到提高ZTZT值的效果；它们的不同在于各自的散射长度值的效果；它们的不同在于各自的散射长度2021-7-1037随着载流子浓度增加，随着载流子浓度增加， 和和均增加，均增加，却减小却减小目标：目标：合适的载流子浓合适的载流子浓度，尽量提高电导率，同度，尽量提高电导率，同时抑制热导率的增长时抑制热导率的增长热电优值热电优值：seebeckseebeck系数系数：电导率（与载流子浓度和迁

16、移率有关电导率（与载流子浓度和迁移率有关）：热导率（包括声子热导和电子热导）热导率（包括声子热导和电子热导）ZnO陶瓷及应用热电热电材料研究过程中瓶颈材料研究过程中瓶颈 = ne = e/ m*k= ke+kL 掺杂：改变费米能级的位置，优化电输运性能；点缺陷（原子质量波动），增强声子散射低维材料：量子限域效应（超晶格等）晶界散射：引入纳米结构 (纳米线生长)增强声子散射，增强声子散射，降低晶格热导率降低晶格热导率2021-7-1038允许准独立允许准独立的改变的改变S, , ZnO陶瓷及应用改善热电性能的途径改善热电性能的途径传统传统3D材料与低维材料中的热电参数材料与低维材料中的热电参数2

17、021-7-10ZnO陶瓷及应用392021-7-1040将热电材料应用于电子产品高热电优值透明化低维化Low-cost Non-toxic Stable (2000 oC) ZnO thin film Large direct wide band gap (3.37 eV)Large exciton binding energy (60 meV)PropertiesFeatures ZnO陶瓷及应用选用选用Al掺杂掺杂ZnO做热电材料做热电材料2021-7-1041Picture（a）From “ZnO nanowires modified with Au nanoparticles for

18、 nonenzymatic amperometric sensing of glucose”ZnO陶瓷及应用制备垂直于基面生长的制备垂直于基面生长的ZnO纳米线纳米线2021-7-1042Fig. Schematic and equipment of thermal evaporationquartz 0.5 mmAu layer 10 nmZn layer 400nmSubstrate temperature: RT Pressure: 2.210-4 Pa Purity: Zn, 99.99%; Al, 99.99%;Au:99.999% Source: Zn 350 oC; Au, Al

19、:1215 oC, 1390 oC /Zn 350 oC; Au, 1350 oC ,Al:1030 oC quartz 0.5 mmAu layer 10 nm Zn-Al layer 400nmquartz 0.5 mmZn-Al layer 400nmZnO陶瓷及应用制备制备原料与工艺原料与工艺2021-7-10ZnO陶瓷及应用432021-7-10ZnO陶瓷及应用44 Structures Properties Crystal structureMorphologyCompositionInterface structureOpticalRigaku dmax 2400 XRD Zei

20、ss supra 35 SEM, Nanosurf naio AFM Oxford inca EDX High resolution transmission electron microscopy (HRTEM, JEOL JEM 2100) Perkinelmer lambda 750S Uv-vis spectrophotometer Relation Thermoelectric properties Japanese Vacuum Polytechnic Companys ZEM-3Analysis The results of SEM images2021-7-10ZnO陶瓷及应用

21、45(b) (a) (c) 2 m2 m2 mSEM images of the doped ZnO films after oxidizing for 90 min at 600 C from different initial constituents of (a) Au/Zn bilayer, (b) Zn-Al single layer, and (c) Au/Zn-Al bilayer.The results of SEM images2021-7-10ZnO陶瓷及应用46Fig. (a) appears that the morphology is formed by dendri

22、tic nano-columns, which is perpendicular to the substrate. This may because of the catalysis of Au on the ZnO growth. The diameters of the columns are about 285.00 nm and distribute uniformly. The column of surface changes to nanoparticle for the doped ZnO oxidized from the Zn-Al and Au/Zn-Al films.

23、 The particle size (106.58 nm) oxidized from the Au/Zn-Al film is much smaller than that (228.40 nm) oxidized from the Zn-Al film. The difference in the surface morphologies of the films oxidized from the Au/Zn and Au/Zn-Al films indicates that not only Au but also Al plays a key role in the oxidati

24、on growth. Al inhibits the growth of nano-column and Au results in a smaller particle size. Thus, the surface morphologies of the films can be controlled by doping Al and Au.The results of XRD2021-7-10ZnO陶瓷及应用47The peaks of the doped ZnO film oxidized from the Au/Zn bilayer are very weak because the

25、 column structure is perpendicular to substrate. For the doped ZnO film oxidized from the Zn-Al single layer, the peaks exhibit the characters of not only suited for ZnO but also other phases associated with Al, Zn and O. The other phases are related to Al2O3 and ZnAl2O4 . This means that excessive

26、Al has been oxidized to aluminium oxide, which is the dopant that changes the microstructure of the doped ZnO films. Compared to the XRD data oxidized from the Au/Zn-Al and Zn-Al films, the amount of diffraction peaks decreased under the catalysis of Au. In addition, the position of the Al2O3 (101)

27、peak is different. Without the catalysis of Au, the positions of the diffraction peaks shift to small angle. This is because more Al3+ was substituted by Zn2 + in the lattice, and the radius of Zn2+ (0.060 nm) is larger than Al3+ radius (0.036 nm). Lattice distortion and internal stress make the dif

28、fraction peaks shift to a small angle.XRD images of the doped ZnO filmsThe results of Transmittance2021-7-10ZnO陶瓷及应用48For the ZnO film oxidized from the Au/Zn film, the transmittance increased with the wavelength of light and was more than 70% for the infrared light (1700-2000 nm). For the ZnO films

29、 oxidized from the Zn-Al and Au/Zn-Al films, the transmittance is about 22%, because that the transmittance is strongly related to the surface structure, vacancy and Al content in the film. The transmittance of the ZnO film oxidized from the Au/Zn bilayer is much higher than that of other films. Thi

30、s is because the column of the Au/Zn case is perpendicular to substrate and isolated from each other. For the Al doped case, they formed non-transparent aluminum oxide in the films. Since the ZnO film with a small particle size has more grain boundaries to improve the transmittance. As a result,the

31、transmittance of the Zn-Al case is slightly higher than that of the Au/Zn-Al case.Transmittance of the doped ZnO filmsThermoelectric properties2021-7-10ZnO陶瓷及应用49V-I curves measured with (a) and without (b) silver conductive adhesive of the doped ZnO filmsHeating furnaceUpper blockLower blockThermoc

32、oupleThin filmCurrent electrodeSilver conductive adhesive Conductive adhesive Quartz holder Schematic diagram of measuring the thermoelectric parameters.Thermoelectric properties2021-7-10ZnO陶瓷及应用50Electrical resistivity (a), Seebeck coefficient S (b), and power factor (c) of the doped ZnO films afte

33、r oxidizing for 90 min at 600 C from different initial constituents of the Au/Zn, Zn-Al, and Au/Zn-Al films.The results of TEM2021-7-10ZnO陶瓷及应用515 nm5 nm(a)(b)HRTEM images of the ZnO films oxidized from the Zn-Al film (a) and the Au/Zn-Al film (b).The results of TEM2021-7-10ZnO陶瓷及应用52(a)(b)300 nm300

34、 nmAl(c)(d)ZnO300 nm300 nmTEM image (a) and the corresponding surface component mapping of Aluminium (b), Zinc (c) and oxygen (d) of the ZnO film oxidized from the Au/Zn-Al film.Conclusions2021-7-10ZnO陶瓷及应用53The effect of Al2O3 and Au dopants on the structure and thermoelectric properties of the dop

35、ed ZnO films fabricated by oxidation the Au/Zn bilayer, Zn-Al single layer and Au/Zn-Al bilayer was studied. SEM, XRD, UV-vis, ZEM-3 results showed that both growth model and dopants have a great effect on the structure, particle size, transmittance and thermoelectric properties of the doped ZnO fil

36、ms. The morphology of the ZnO film oxidized from the Au/Zn bilayer was formed by the dendritic nano-column which was perpendicular to substrate due to the Au catalysis and was transformed to nanoparticle with doping Al. However, doping excessive concentration of Al decreased the transmittance of the

37、 films. The Au dopant decreased the particle size and inhibited the growth of Al2O3. The mutually independent column and without dopant Al2O3 resulted in a large resistivity of the ZnO film oxidized from the Au/Zn film. While the Al2O3 dopant improved the conductivity of the ZnO films oxidized from

38、the Au/Zn-Al and Zn-Al films, and the values of resistivity were in range of the semiconductor. The values of the Seebeck coefficient basically ascended in magnitude with increasing temperature small pseudo gap. The largest power factor of the ZnO film oxidized from the Zn-Al single layer was 3.9951

39、0-5 W/ (mK2) at 240 C. Therefore, the study provides a method to modify the structure and electrical properties of doped ZnO films.强磁场应用的原理强磁场应用的原理2021-7-10ZnO陶瓷及应用542021-7-10ZnO陶瓷及应用55制备制备原料与工艺原料与工艺The results of SEM images2021-7-10ZnO陶瓷及应用561 m(a)(c)(d)2 mBlackGrayish white2 m2 m2 m(b)Isolated isl

40、ands(f)Point A(e)A SEM images of the Au- and Al-doped ZnO films after oxidation for 3 h at 420 C with and without an application of high magnetic field. (a) Au/Zn 0 T; (b) Au/Zn 12 T; (c) Au/Zn-Al 0 T;(d) Au/Zn-Al 12 T; (e) Enlarged schematic picture of the region in figure 1(b); (f) Energy dispersi

41、ve X-ray spectrometer (EDS) spectrograms of figure 1 (e).The results of XRD2021-7-10ZnO陶瓷及应用57The peaks of the Au/Zn 0 T film are very weak. That the column cant be recognized is because the particles are too small and the crystallization is too weak. For the Au/Zn 12 T film, the peaks exhibit the c

42、haracters of suiting for not only ZnO but also other phase associated with Au. That indicates that Au did not completely enter into the inside of the ZnO crystal lattice. The Au/Zn 12 T films has the strongest (002) peak while an (101) diffraction peak was also observed in the XRD profiles. The resu

43、lts indicate that these films have preferred c-axis orientation. For the doped ZnO oxidized from the Au/Zn-Al bilayer, the diffraction trace of the (002) plane was weakened, while that of the (101) and (100) plane was enhanced. The c-axis preferred orientation of the films becomes indistinct by the

44、high concentration of Al due to the degradation of the film crystallinity. Meanwhile, there are no diffraction peaks from other phase. This indicates that the Zn element was all oxidized to ZnO. With the addition of the Al element, a new diffraction peak was observed in the XRD profile at 42.5, which corresponds to the (006) plane of Al2O3. The inte