《功能陶瓷讲义》PPT课件.ppt

Electronic Ceramics and Their Applications,X.M.Chen(陈湘明)Department of Materials Science E-mail:Web:http:/,Brief Introduction of X.M.Chen,Was born in Hunan 1959B.S.Dept.Mater.Sci.&Eng.,Central South University in 1981PhD Dept.Mater.Sci.&Metallurgy,The University of Tokyo in 1991Research Scientist at Yokohama R&D Labs.,Furukawa Electric Co.Ltd.(Japan),1991-1994Associate Professor,Dept.Mater.Sci.Eng.,Zhejiang Univ.1994-1996Professor,Dept.Mater.Sci.Eng.,Zhejiang Univ.,Since 1996Distinguished Young Scientist Foundation of NSFC in 2000Professor of“Changjiang Scholar Program”2002Member of International Advisory Board of MMA2000,MMA2002,MMA2006Chairman,MMA-2004(Inuyama,Japan)&MMA-2008(Hangzhou,China)Member of Executive Board,Asian Electroceramics Association(AECA).Authored or co-authored more than 140 papers in pier-reviewed international journals,Research Activities in X.M.Chens Group,微波介质陶瓷及其应用(Microwave dielectric ceramics and their applications)中介电常数微波介质陶瓷新体系低介电常数微波介质陶瓷新体系叠层介质谐振器可调谐介电薄膜铁电与介电新材料(Ferroelectric and dielectric new materials)巨介电常数材料(Giant dielectric constant materials)非铅铁电与弛豫铁电陶瓷(Pb-free ferroelectric and relaxor ferroelectric ceramics)微图案铁电薄膜(Micro-patterned ferroelectric thin films)复相与多功能耦合陶瓷(Composite and multifunctional ceramics)磁电复相陶瓷(Magetoelectric composite ceramics)多铁性材料(Multiferroic materials)磁性电介质(Magnetic dielectrics),功能陶瓷的基本概念,与结构陶瓷相对应的概念，主要指具备特定的电、磁、声、光、热等物理性能的陶瓷材料；电子陶瓷是功能陶瓷的主体；电子陶瓷：介电陶瓷(绝缘陶瓷)、铁电陶瓷、反铁电陶瓷、压电陶瓷、热释电陶瓷、半导体陶瓷、电光陶瓷、磁性陶瓷等在电子、通讯、军事、以及家电技术中有着广泛的应用。,功能陶瓷的学科关系,学科基础：固体物理、固体化学、电磁学、材料科学基础相关学科：电子、通讯、仪器仪表等,无机非金属材料,功能材料,功能陶瓷,功能陶瓷现代电子技术的三大物质基础之一,半导体材料,电介质材料(功能陶瓷),光电子材料,微电子学,固体电子学,光电子学,电子材料,Primary Contents,Elements of Dielectrics(电介质)and Ceramic InsulatorsFerroelectric(铁电),Relaxor Ferroelectric(驰豫铁电),Antiferroelectric(反铁电)Ceramics and Ceramic Capacitors(电容器)Microwave Dielectric Ceramics(微波介质陶瓷)Piezoelectric(压电)and Opto-electric CeramicsCeramic SensorsZnO Varistors(变阻器)Conducting Ceramics,Chapter 1 Elements of Dielectrics and Ceramic Insulators,I.Elements of Dielectrics,物质按导电性能的分类,载流子长程运动与位移传导、宏观电流导体：金属、部分非金属半导体：部分非金属单质与化合物绝缘体（无载流子长程运动与位移）：大部分非金属单质与化合物载流子短程运动与位移极化(Polarization)电介质（绝缘体+半导体；通常为绝缘体）,电介质的基本物理概念-极化,极化-正负电荷中心偏移偶极矩(dipole moment)p=Qdx(1.1)极化强度PP=dp/dV=Njmj(1.2)(Nj=number of dipoles of type j;mj=average dipole moment)mj=aj E(1.3)aj-polarizability of average dipole moment;E-local electric fieldP=sp(surface charge density)(1.4),极化机理,at=as+ao+ai+ae(1.5)ae-Electronic(Atomic)Polarization;ai-Ionic Polarization;ao-Orientation(Dipolar)Polarization;as-Space Charge or Diffusional Polarization,电位移D、电场强度E与极化强度P的关系,For case a):E=s/e0(1.6)s-surface charge densityFor case b):E=(sT-sP)/e0(1.7)sT total surface charge density;sP polarazation charge densitySince P=sP and sT=D(electric displacement)e0 E=P-D(1.8)D=e0 E+P(1.9)If the dielectric is linear,P=ce e0 E,so that D=e0 E+ce e0 E=(1+ce)e0 E(1.10)where,ce is electric susceptibility,a tensor of the second rank,介电常数(Dielectric Constant),Since D=sT,QT/A=(1+ce)e0 U/h(1.11)QT=(1+ce)e0 UA/h(1.12)C=QT/U=(1+ce)e0 A/h(1.13)Since vacuum has zero susceptibility,C0=e0 A/h(1.14)If the space between the plates is filled with a dielectric of susceptibility ce,the capacitance is increased by a factor 1+ce.Permittivity e of the dielectric is defined by e=e0(1+ce)(1.15)Dielectric constant(relative permittivity)er=e/e0=1+ce(1.16),An individual atom or ion in a dielectric is not subjected directly to an applied field but to a local field.The internal macroscopic field Em is the resultant of applied external field Ea and depolarizing field Edp,i.e.Ea-Edp.It is assumed that the solid can be regarded as comprising identifiable polarizable entities on the atomic scale.The local field EL(or Lorentz field)differ from Em since the latter is arrived at by considering the dielectric as a continuum.EL=Em+Ep+Ed(1.17)where,Ep-the contribution from the charges at the surface of the spherical cavity(imaging for the moment that the sphere of material is removed);Ed-due to the dipoles within the boundary.,Applied External Field,Internal Macroscopic Field&Local(Lorentz)Field,Clausius-Mosotti Equation,Ep can be shown to be P/3e0,and Ed=0 for certain crystals of high symmetry and glasses.So that,EL=Em+P/3e0=Ea-Edp+P/3e0(1.18)In more general case,it is assumed that EL=Em+gP(1.19)in which g is the“internal field constant”The dipole moment p induced in the entity can be now written as p=a EL(1.20)If it is assumed that all entities are of the same type and have a density N,then P=Np=Na(Em+gP)(1.21)Or P/e0Em=ce=Na/e0/(1-Nag)(1.22)In the particular case for which g=1/3eo,we have the Clausius-Mosotti Equation(er-1)/(er+2)=Na/3e0(1.23),介电损耗(Dielectric Loss),介电损耗(Dielectric Loss),对于理想电介质，极化能适时响应外电场变化，电位移与电场的相位相同(电流超前p/2)不产生能量损耗；而对于实际电介质，极化不能适时响应外电场变化(滞后于电场d-损耗角),而出现介电弛豫 介电损耗。介电损耗的数学描述 E=E0exp(iwt)(1.24)D=D0expi(wt-d)(1.25)利用D=k*E，得 k*=ksexp(-id)=ks(cond-isind)(1.26)其中，ks-静态介电常数(=D0/E0),介电损耗(Dielectric Loss),利用复介电常数的概念 k*=k-ik”=e*/e0=(e-ie”)/e0(1.27)k=kscosd(1.28)k”=kssind(1.29)tand=k”/k=e”/e(1.30)tand即为介电损耗物理意义 极化过程中消耗的能量与储存的能量的比值电介质的品质因数：Q=1/tand,Resonance Effects,In the case of atomic and ionic polarization,the electrons and ions behave,to a first approximation,as though bound to equilibrium positions by linear springs so that the restoring force is proportional to displacement,a damping factor g is included in the equation of motion.(1.31)Solving(1.31)and ignoring the transient term yields(1.32)Since ex(t)is the induced dipole moment per atom,the complex polarization P*is given by(1.33),Resonance Effects,And(1.34)So that(1.35)By equating real and imaginary parts(1.36)(1.37)The above the contributions of ionic and electronic polarization,which are sensibly independent of temperature,the resonance curves are also.,Variation in and with frequency close to a resonance frequency w0.,Relaxation Effects,In contrast with the electronic and ionic polarization processes,the diffusional polarization and depolarization processes are relatively slow and strongly temperature dependent.The diffusional polarization Pd approaches its final static value Pds according the following equation(1.38)where,t is a relaxation time.Integrating(1.38)with initial condition Pd=0 when t=0 gives(1.39)To account for alternating applied field,Eq.(1.38)should be modified to(1.40)where,ers is the low frequency dielectric constant.,Relaxation Effects&Debye Equations,Equation(1.40)can be integrated to give(1.41)By neglecting the transient Cexp(-t/t),we can get(1.42)The Debye Equations are obtained by separating the real and imaginary parts of Eq.(1.42)(1.43)(1.44)The relaxation frequency is w=1/t,Dielectric Dispersion,With increasing frequency,dielectric constant generally decrease,and some peaks appear for dielectric loss.Origins of dielectric dispersion:Rrelaxation process(orientation and space charge polarization)Resonance process(electronic and ionic polarization)Available frequencies for various polarization mechanisms:Space charge polarization:102HzOrientation polarization:106HzIonic polarization:1013HzElectronic polarization:1016Hz,Cole-Cole Distributions,Cole and Cole(1942)modified equation(1.42)by including an exponent a(1.45)The distribution is obtained by plotting er”as a function of er,yielding what is termed the Cole-Cole distribution.Using the circuit parameters,we obtain(1.46)Or(1.47),k”or e”,k or e,C1/e0,(C1+C2)/e0,w0RC2=1,Indicates high losses,RC circuit,Cole-Cole plot,Cole-Cole Plot and the RC Circuit,Physical Meaning of Cole-Cole Plot,The Cole-Cole plot of a material is a measure of the various relaxation times for a specific dielectric material.A very narrow distribution of relaxation times perfect dielectric.This indicates that only one primary mechanism exists for the polarization within the material;A tail in the distribution indicates a large distribution of relaxation time;A large range of relaxation times can indicate multiple polarization mechanisms but also losses due to conduction.A perfect or low loss dielectric would have a Cole-Cole plot that is nearly a semicircle;A poor or high loss dielectric would have a non-bounded increasing er”with increasing er.,Dielectric Strength(介电强度),Dielectric breakdown(介电击穿):All dielectrics when placed in an electric field will lose their insulating properties if the field exceeds a certain critical value.This phenomenon is called dielectric breakdown.Dielectric strength 1.48)Dielectric breakdown mechanismsIntrinsic breakdownThermal breakdownInonization breakdownElectrochemical breakdown,Factors Affecting Dielectric Strength,Composition:amorphous or crystalline nature,presence of mobile ions;Microstructural features:porosity,grain size,cracks,flaws,secondary phases;Measurement parameters:electrode configuration,specimen thickness,temperature,time,frequency,humidity and heat transfer conditions.,Chapter 1 Elements of Dielectrics and Ceramic Insulators,II.Ceramic Insulators,Intoduction,Function of insulator in electric circuits:Physical separation of conductors and the regulation or prevention of current flow between them;Ancillary but important other functions are to provide mechanical support,heat dissipation and environmental protection for the conductors Advantages of ceramic insulators:Materials type used as insulators:linear dielectricsTypical elements of ceramic insulator:ceramic substrates,ceramic packages,Property Requirements to Ceramic Insulators,Dielectric constant;Dielectric loss;Dielectric strength;Resistivity(1.49)Thermal conductivity;Thermal expansion coefficient;Mechanical properties.,Property Criteria for Good Ceramic Insulators,Dielectric constant:not greater than 30;Electric resistivity:not less than 1012 W-cm;Dielectric loss(dissipation factor):not larger than 0.001;Dielectric strength:not less than 5.0kV/mmDielectric loss factor:not larger than 0.03,Table 1.1 Dielectric properties of Ceramic Insulators,Table 1.1 Dielectric properties of Ceramic Insulators,Table 1.2 Thermomechanical Properties of Ceramic Insulators,Table 1.2 Thermomechanical Properties of Ceramic Insulators,Materials Systems for Ceramic Insulators,GlassesPorcelainsSteatite(滑石,MgO.SiO2),Forstrite(镁橄榄石,2MgO.SiO2),Cordierite(堇青石,2MgO.2Al2O3.5SiO2),Spinel(尖晶石,MgO.Al2O3),Mullite(莫来石,3Al2O3.2SiO2),Single oxide and nitrides ceramicsAlumina(Al2O3),Magnesia(MgO),Boron nitride(BN),Aluminum nitride(AlN),Silicon nitride(Si3N4),Property Criteria for Good Ceramic Insulators,Dielectric constant:not greater than 30;Electric resistivity:not less than 1012 W-cm;Dielectric loss(dissipation factor):not larger than 0.001;Dielectric strength:not less than 5.0kV/mmDielectric loss factor:not larger than 0.03,Property Target for Ceramic Substrates,Low dielectric constant:e7Low dielectric loss:tand4x10-4High resistivity:r1012-1014W.cmHigh thermal conductivity;Coefficient of thermal expansion close to that of Si.,作业,就下列问题之一进行专题调研、在独自撰写小论文的基础上，自愿组合成小组(10-11人)、共同准备PP T文件，并推举代表演讲(15分钟)。*1)绝缘陶瓷的材料体系2)陶瓷基板的研究现状与发展趋势*第2周准备论文与讲稿、9/21演讲,