Functional solid state materials Materials History the secret for transmuting base metals into precious gold Electrical properties Optical properties MEchanical properties Alchemist Material Chemist Development of Materials vs Human Society Historical Perspective began to make tools The history of human society can be marked with inorganic NAtural matene ended abe ut 000 ey, ns ago with intron.o of the Stone Age ah Historical Perspecti ron->steel- Advanced materials ammered or cast into a variety of shapes er by alloying, corrode only slowly after a surface oxid The Iron Age began about 3000 years ago an se of iron and steel, a stronger and cheaper a common perso Materials: throughout the Iron Age many new telligent design of new mato g, and performance of materialeng composites. ). Understanding of the relationship among Structure- Composition Properties Types of Materials Let us classify materials according to the way the atoms are Metals: valence electrons the ions togethe A better understanding of heat well, are shiny if miconductors: the bonding is covalent (electrons are shar rogress in the strength to tensity ratio of materials that resulted in a wide variety ucts. from dents materials to tennis racquets. r Waals forces, and usually based on C and H. They lightweight. Examples plastic, rubes(100-1000C), and ar mpose at moder
1 Functional Solid State Materials Electrical properties Optical properties Magnetic properties Mechanical properties “the secret for transmuting base metals into precious gold” Materials & History Stone age Bronze age Iron age Silicon age Alchemist Material Chemist Development of Materials vs Human Society The history of human society can be marked with inorganic materials. Historical Perspective Stone ® Bronze ® Iron ®steel ® Advanced materials Beginning of the Material Science ¾ People began to make tools from stone ¾ Start of the Stone Age about two million years ago. Natural materials: stone, wood, clay, skins, etc. The Stone Age ended about 5000 years ago with introduction of Bronze in the East Asia. Bronze is an alloy (copper + < 25% of tin + other elements). Bronze: can be hammered or cast into a variety of shapes, can be made harder by alloying, corrode only slowly after a surface oxide film forms. The Iron Age began about 3000 years ago and continues today. Use of iron and steel, a stronger and cheaper material changed drastically daily life of a common person. Age of Advanced Materials: throughout the Iron Age many new types of materials have been introduced (ceramic, semiconductors, polymers, composites… ). Understanding of the relationship among structure, properties, processing, and performance of materials. Intelligent design of new materials. Historical Perspective A better understanding of structure-compositionproperties relations has lead to a remarkable progress in properties of materials. Example is the dramatic progress in the strength to density ratio of materials, that resulted in a wide variety of new products, from dental materials to tennis racquets. Structure-Composition-Properties Types of Materials Let us classify materials according to the way the atoms are bound together. •Metals: valence electrons are detached from atoms, and spread in an “electron sea”that “glues”the ions together. Strong, ductile, conduct electricity and heat well, are shiny if polished. •Semiconductors: the bonding is covalent (electrons are shared between atoms). Their electrical properties depend strongly on minute proportions of contaminants. Examples: Si, Ge, GaAs. •Ceramics: atoms behave like either positive or negative ions, and are bound by Coulomb forces. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and carbides). Hard, brittle, insulators. Examples: glass, porcelain. •Polymers: are bound by covalent forces and also by weak van der Waals forces, and usually based on C and H. They decompose at moderate temperatures (100-400°C), and are lightweight. Examples: plastic, rubber
Materials Tetrahedron Life Cycle of Materials Performance engineering materials materials Synthesis cle/r roduct Design Structure and [chemistryl Composition Properties Electric Properties of Crystals pRoperties are the way the material responds to the PMechanical properties- response to mechanical forces, Crystals can be classified by electric properties strength. ete COnductors and magnetic fields, conductivity, et -response electrical E Dielectric crystals Thermal properties are related to transmission of heat Semiconductors SUperconductors aChemical Stability in contact with the environment- corrosion resistance Dielectric Material Dielectric Properties A dielectric material is an insulator in which electric dipoles can be induced by the electric The biggest difference between dielectric field (or permanent dipoles can exist even materials and conductors is that the transfer without electric field), that is where positive ways of electrons are totally different nd negative charge are separated on an pielectric--in manner of induced polarization conductor manner of conduction
2 Materials Tetrahedron Performance Properties Structure and Composition Synthesis and Processing [chemistry & engineering] [chemistry & physics] [engineering] [chemistry] Life Cycle of Materials Synthesis and Processing Engineered Materials Product Design Manufacture Assembly Waste Applications Recycle/Reuse Raw Materials Properties are the way the material responds to the environment and external forces. Mechanical properties ¾ response to mechanical forces, strength, etc. Electricaland Magnetic properties ¾ response electrical and magnetic fields, conductivity, etc. Thermal properties are related to transmission of heat and heat capacity. Opticalproperties include to absorption, transmission and scattering of light. Chemical Stability in contact with the environment ¾ corrosion resistance. Properties Electric Properties of Crystals Crystals can be classified by electric properties: Conductors Dielectric crystals Semiconductors Superconductors Dielectric Properties The biggest difference between dielectric materials and conductors is that the transfer ways of electrons are totally different: Dielectric¾¾in manner of induced polarization conductor ¾¾in manner of conduction Dielectric Material A dielectric material is an insulator in which electric dipoles can be induced by the electric field (or permanent dipoles can exist even without electric field), that is where positive and negative charge are separated on an atomic or molecular level + _ + _ + _
Dielectric Materials Mechanisms of Dipole formation and/or orientation along the external Polarization redistribution so that the surface nearest to the positive apacitor plate is negatively charged and vice versa at the surface, Q ⊙⊙ Q net positive charge at ionic polarization The process of dipole formation/alignment in electric field is called polarization and is described by P=Q7A molecular (orientation) polarization Dipole moments Basic Conception Orientation of dipole moments a Dielectric- material that is electrically insulating or can be made to exhibit an electrie dipole. Permittivity -ratio of the electric displacement in a Capacitance-The ratio of charge to potential on an electrically charged, isolated conductor Voong Dielectric strength-magnitude of the electrie field necessary to produce breakdown Relative Permittivity Dielectric Strength a Very high electric fields(>10 V/m)can excite s The resultant capacitance can then be electrons to the conduction band and accelerate measured due to the dielectric them to such high energies that they can, in turn, free other electrons, in an avalanche process(or C=EAld electrical discharge). The field necessary to start the dielectric constant E=E/ Eo the avalanche process is called dielectric strength the dielectric constant, or relative a The dielectric strength is a measure of how much rmittivity, is the ratio of the permittivity of be applied to a dielectric before electric he material to the permittivity of free space current begins to are across the dielectric (1=8854x1012Fm) ross the dielectric is known as dielectric a Dielectric strength has the units of vim
3 Dipole formation and/or orientation along the external electric field in the capacitor causes a charge redistribution so that the surface nearest to the positive capacitor plate is negatively charged and vice versa. + + + + + + + + - - - - - - - - - - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + Q0+Q’ -Q0 -Q’ region of no net charge net negative charge at the surface, -Q’ net positive charge at the surface, Q’= PA P Dielectric Materials The process of dipole formation/alignment in electric field is called polarization and is described by P = Q’/A electronic polarization ionic polarization molecular (orientation) polarization Mechanisms of Polarization Dipole Moments Orientation of dipole moments Basic Conception Dielectric¾ material that is electrically insulating or can be made to exhibit an electric dipole. ß Permittivity ¾ ratio of the electric displacement in a medium to the intensity of the electrical field producing it. ß Capacitance ¾ The ratio of charge to potential on an electrically charged, isolated conductor ß Dielectric strength ¾ magnitude of the electric field necessary to produce breakdown . Relative Permittivity The resultant capacitance can then be measured due to the dielectric: C = erA/d ß the dielectric constant er= e/ e0 ß the dielectric constant, or relative permittivity, is the ratio of the permittivity of the material to the permittivity of free space (e0=8.854x10-12 F·m-1) Dielectric Strength Very high electric fields (>108 V/m) can excite electrons to the conduction band and accelerate them to such high energies that they can, in turn, free other electrons, in an avalanche process (or electrical discharge). The field necessary to start the avalanche process is called dielectric strength or breakdown strength. The dielectric strength is a measure of how much voltage can be applied to a dielectric before electric current begins to arc across the dielectric Arcing across the dielectric is known as dielectric breakdown. Dielectric strength has the units of V/m
Dielectric material The Relations of Dielectric Crystals na dielectric material is a material that is nonmetallic and exhibits or may be made to exhibit an electric dipole sThe dielectric crystals can d as aA dielectric material is characterized and selected according be to its dielectric constant. Zr. often called the relati permittivity. There are many ceramics and polymers that exhibit dielectric behavio lectric Applications for dielectric materia ferroelectric Dielectric materials to insulate electrical conductors tThe ber in the Dielectrie materials used in capacitor parentheses is the point Communications (radio, radar and microwave groups that the crystal Microelectronics possibly exist Piezoelectricity Piezoelectricity fThe piezoelectric effect was first mentioned in 1817 by the materials, application of external forces produces an electric(polarization) field and vice demonstrated by Pierre and Jacques Curie in 1880 versa tThe direct piezoelectric effect consists of the ability of certain piezoelectric effect and converse piezoelectric effect Some dielectrics have a crystal structure with one polar on of an externally applied force is. mechanical deformation of the crystal lattice APplications of piezoeled causes electric displacement On the other hand, the I polar axis causes a deformation of the crystal lattice gauges et al)The direct piezoelectric effect has been widely when electric charges are being displaced. This is sed in transducers design (accelerometers, force and pressure called converse piezoelectric effect. pIezoelectric materials include barium titanate eccording to the inverse piezoelectric effect, an electric field BaTiOa, lead zirconate PbZrO3 quartz piezoelectric effect has been applied in actuators design. Piezoelectric Effect basics Piezoelectric Effect basic trie charge How to produce piezoelectric effect ly electric field Mechanical deformation produced a Dipole each molecule has a polarization, one end is more negatively charged and the other end is positively a Monocrystal the polar axes of all of the dipoles lie in one a Polycrystal there are different regions within the material that have a different polar axis. a) Material without stress/ charge b) Compress same polarity e)Stretched= opposite polarity d)Opposite voltage= expand tttttttttt e)Same voltage =c DAC signal=vibrate 每y
4 Dielectric Material A dielectric material is a material that is nonmetallic and exhibits or may be made to exhibit an electric dipole structure. A dielectric material is characterized and selected according to its dielectric constant, Σr, often called the relative permittivity. There are many ceramics and polymers that exhibit dielectric behavior. Applications for dielectric materials –Dielectric materials to insulate electrical conductors –Dielectric materials used in capacitors –Communications (radio, radar and microwave) –Microelectronics The Relations of Dielectric Crystals The dielectric crystals can be classified as: dielectric piezoelectric pyroelectric ferroelectric The number in the parentheses is the point groups that the crystal possibly exist Piezoelectricity In some ceramic materials, application of external forces produces an electric (polarization) field and viceversa piezoelectric effect and converse piezoelectric effect: Some dielectrics have a crystal structure with one polar axis. mechanical deformation of the crystal lattice causes electric displacement. On the other hand, the polar axis causes a deformation of the crystal lattice when electric charges are being displaced. This is called converse piezoelectric effect. Piezoelectric materials include barium titanate BaTiO3 , lead zirconate PbZrO3 , quartz. Piezoelectricity The piezoelectric effect was first mentioned in 1817 by the French mineralogist Rene Just Hauy. It was first demonstrated by Pierre and Jacques Curie in 1880. The direct piezoelectric effect consists of the ability of certain crystalline materials (i.e. ceramics) to generate an electrical charge in proportion of an externally applied force. Applications of piezoelectric materials is based on conversion of mechanical strain into electricity (microphones, strain gauges et al.)The direct piezoelectric effect has been widely used in transducers design (accelerometers, force and pressure transducers ...). According to the inverse piezoelectric effect, an electric field induces a deformation of the piezoelectric material. The inverse piezoelectric effect has been applied in actuators design. Piezoelectric Effect Basics Apply mechanical stress Þ Electric charge produced Apply electric field Þ Mechanical deformation produced Dipole: each molecule has a polarization, one end is more negatively charged and the other end is positively charged. Monocrystal: the polar axes of all of the dipoles lie in one direction. ¾¾ Symmetrical Polycrystal: there are different regions within the material that have a different polar axis. ¾¾ Asymmetrical Piezoelectric Effect Basics ß How to produce piezoelectric effect a) Material without stress / charge b) Compress Þ same polarity c) Stretched Þ opposite polarity d) Opposite voltage Þ expand e) Same voltage Þ compress f) AC signal Þ vibrate
Rfall tetrahedra have the sam Piezoelectricity The Piezoelectric orientation or some other Effect vs Crystal mutual orientation that does no o( Greek: piezo"to press") Structure the action of all dipoles adds up 9 Some ionic crystals with polar axis d the whole crvstal becomes show a piezoelectric effect ryor opposite faces of the external pressure causes ACrystals can only be deformation and results in piezoelectric if they are non- centrosymmetric SPhalerite, tourmaline, ammonium chloride and quartz Piezoelectricity AApplication of pressure to a piezoelectric crystal Piezoelectric materials have crvstal structures that lack displaces the crystal ions with respect to each other When the crystal is stressed however it develops a NE variation AThis change of polarization can be detected as a voltage across the crystal and this effect is referred to as piezoelectricity Piezoelectric crys mechanical pulses are to be concerted to electrical pplication of stress to AThe opposite effect to piezoelectricity is ystal, the net polarization is the crystal gives rise to a electroconstriction which is an effect in which an electric field is used to produce a change in the agnitude of the dipole moments dimensions of a piezoelectric crystal: e.g. Mechanical lding the three symmetry vibrations are induced in the quartz with the aid of electric pulses Piezoelectricity Applications of Piezoelectric Crystals . Crystals where electrical polarization generated by mechanical stress -in general, they are Mechanical to Electrical Conversio centrosymmetrIc Phonograph cartridges eStrain shifts the relative positions of the positive and negative charges, giving ri a net electric Microphones Vibration sensors +In 32 crystallographic point groups, 21 Accelerometers possess inversion symmetry elements, plu Photoflash actuators oic has a combination of symmetries 20 groups can be piezoelectric Gas igniter Many crystals with tetrahedral structure units (SiO, ZnO etc ).shearing stress causes distortional train of tetrahedry
5 Piezoelectricity (Greek: piezo "to press") Some ionic crystals with polar axis show a piezoelectric effect. The Piezoelectric Effect vs Crystal Structure If all tetrahedra have the same orientation or some other mutual orientation that does not allow for a compensation, then the action of all dipoles adds up and the whole crystal becomes a dipole. Two opposite faces of the crystal develop opposite electric charges. Crystals can only be piezoelectric if they are noncentrosymmetric. Sphalerite, tourmaline, ammonium chloride and quartz are examples. external pressure causes deformation and results in electric dipole Piezoelectricity Piezoelectric materials have crystal structures that lack inversion symmetry but show NO spontaneous polarization Þ When the crystal is stressed however it develops a NET polarization in an unstressed piezoelectric crystal, the net polarization is equal to zero (arrows indicate the magnitude of the dipole moments along the three symmetry directions of the crystal) application of stress to the crystal gives rise to a net polarization p STRESS P Application of pressure to a piezoelectric crystal displaces the crystal ions with respect to each other and so causes a change in polarization. This change of polarization can be detected as a voltage across the crystal and this effect is referred to as piezoelectricity. Piezoelectric crystal serve whenever mechanical pulses are to be concerted to electrical signals, e.g. in microphones. The opposite effect to piezoelectricity is electroconstriction which is an effect in which an electric field is used to produce a change in the dimensions of a piezoelectric crystal: e.g. Mechanical vibrations are induced in the quartz with the aid of electric pulses. Piezoelectricity Crystals where electrical polarization generated by mechanical stress ¾¾ in general, they are noncentrosymmetric. Strain shifts the relative positions of the positive and negative charges, giving rise to a net electric dipole. In 32 crystallographic point groups, 21 do not possess inversion symmetry elements, plus one cubic has a combination of symmetries, thus, only 20 groups can be piezoelectric. Many crystals with tetrahedral structure units (SiO2 , ZnO etc.),shearing stress causes distortional strain of tetrahedra. Applications of Piezoelectric Crystals ß Mechanical to Electrical Conversion –Phonograph cartridges –Microphones –Vibration sensors –Accelerometers –Photoflash actuators –Gas igniters –Fuses