材料科學(xué)與工程基礎(chǔ)：第2章 材料的結(jié)構(gòu)2

1、組成和結(jié)合鍵1. 組成 廣義：除有機(jī)物和金屬以外。 常見的陶瓷、玻璃、水泥、耐火材料 組分components：硅酸鹽類 氧化物類，氮、碳（不含H）。2. 結(jié)合鍵 bonding type 離子鍵 正負(fù)離子、鍵強(qiáng)度高、緊密堆積、無 方向性， 金屬氧化物，氧化鎂、氧化鋁 共價(jià)鍵 共用電子對、有方向性 如金鋼石、 混合鍵（離子、共價(jià)），大多數(shù)。 混合鍵-離子鍵和共價(jià)鍵之間的過渡。 元素電負(fù)性的大小，。 2.6 Ceramic Crystal StructuresIt can be described by associating each lattice point with a group of

2、 atoms. 晶體結(jié)構(gòu)空間點(diǎn)陣結(jié)構(gòu)基元Crystal Structures2.6 Ceramic Crystal StructuresCation（陽離子）and Anion（陰離子） Ceramic Crystal StructuresCarbonSilicon and oxygen結(jié)構(gòu)基元(原子)p31 離子鍵，無方向性。正離子周圍配位多個(gè)負(fù)離子， 離子的堆積受鄰近質(zhì)點(diǎn)異號電荷及化學(xué)量比限制 堆積形式?jīng)Q定于正負(fù)離子的電荷數(shù)和相對大小離子晶體( Ionic Crystal )2.6 Ceramic Crystal Structures Cation（陽離子）and Anion（陰離子） C

3、ations (metallic ions): are positively charged，because they have given up their valence electrons Anions( nonmetallic ions): are negatively charged, because they have accept valence electrons from cations.Examples:Cations: Na (sodium), Ca(calcium) and so onAnions: Cl (chlorine) , F (fluorine) and so

4、 on.p38(2) The relative sizes of the cations and anions. Factors:(1)The magnitude of the electrical charge on each of the component ions. (Electrically neutral)p38CaF2 (calcium fluoride): Ca2+:two positive charges F-: a single negative chargeThe size or ionic radii of the cations and anions (rC and

5、rA) .The coordination numbers and geometriesp40 配位數(shù) CN 正負(fù)離子半徑比 R/R 負(fù)離子配位多面體2 00.155 線 性 配 位30.1550.225 等 邊 三 角 形40.2250.414 正 四 面 體60.4140.732 正 八 面 體80.7321.000 立 方 體EXAMPLE PROBLEM 3.4Show that the minimum cation-to-anion radius ratio for the coordination number 3 is 0.155SOLUTIONFor this coordina

6、tion, the small cation is surrounded by three anions to form an equilateral triangle as shown belowtriangle ABC; the centers of all four ions are coplanar.This boils down to a relatively simple plane trigonometry problem. Consideration of the right triangle APO makes it clear that the side lengths a

7、re related to the anion and cation radii rA and rC as and Furthermore, the side length ratio AP/AO is a function of the angle as The magnitude of is 30, since line AO bisects the 60 angle BAC. Thus, Or, solving for the cationanion radius ratio,Typical Ceramic Crystal StructureAB type crystal structu

8、resAmBp type crystal structuresAmBnOp type crystal structuresp41AB type crystal structures (1) Sodium Chloride structure (Rock salt structure)(食鹽結(jié)構(gòu)，氯化鈉結(jié)構(gòu)）p41Coordination numbercoordination number = 6(for both cations and anions)StructureFCC, Cl- ions at FCC positions; Na+ at the four octahedral site

9、s.The center of the 12 cube edges Other compoundsMagnesium oxide (MgO) Calcium oxide (CaO),Iron oxide (FeO)Cl- Na+p41（2）Cesium Chloride Structure （氯化銫結(jié)構(gòu)）Coordination numberStructure Simple cubic, Cs+ fill cubic interstitial sites by the Cl- , but not BCCOther compoundsCesium Bromide (CsBr), Cesium I

10、odide (CsI), Titanium Chloride( TiCl), Ammonium Chloride(NH4Cl) Coordination number = 8 (for both ion types)Cl- Cs+p41（3） Zinc Blende Structure (ZnS)（硫化鋅結(jié)構(gòu)）S(001)p42Coordination number coordination number = 4Structure All corner and face positions are occupied by S anions, Zn fill interior tetrahedr

11、al positions. Other compounds Gallium Arsenide (GaAs), - semiconductorsFluorite Structure(CaF2)(氟化鈣結(jié)構(gòu))AB2 type crystal structuresCoordination number coordination number = 8Structure Similar to CsCl, half the center cube positions are occupied by Ca 2+ , F anions locate at the corners.Other compounds

12、Cubic Zirconia (ZrO2), Thorium Oxide (ThO2) Uranium Oxide (UO2), Cerium Oxide (CeO2)p42Perovskite Structure (CaTiO3)(鈣鈦礦晶體結(jié)構(gòu))(a) unit cell structure (b) Ca cation coordination number 12AmBnOp type crystal structuresp43Perovskite Structure (CaTiO3)Structure Ca 2+ cations occupy the cube corner; Ti 4+

13、 cations occupy cube center, O 2- anions occupy the six face centers of the perovskite unit cell.Other compounds Barium Titanate(BaTiO3) (capacitors for electronic applications )p43 立方晶系 Ca2+ 立方體頂角 配位數(shù)12 O2- 面心 配位數(shù)6， Ti4+ 體心 配位數(shù)6 位于八面體間隙 TiO68-八面體 Ti4+八面體中心 Corundum Structure (-Al2O3 alpha alumina)-

14、Al2O3 structure(a) crystal structure (b) close-packed modelCorundum Structure (-Al2O3 alpha alumina)(剛玉)Structure Oxygen anions pack in a hexagonal arrangement; aluminum cations occupy some of the available positions. Application Most widely ceramic material : spark plugs, refractories, electronic p

15、ackaging substrates and abrasives.Covalent StructuresDiamond Cubic Structure （金剛石結(jié)構(gòu)）p48 共價(jià)晶體(Covalent Crystal)： 共價(jià)鍵；有方向性、飽和性， 配位數(shù)和方向受限制（配位須成鍵） 多由非金屬元素組成(A族) N族元素共價(jià)晶體的配位數(shù)為（8N）。 ZnS DiamondStructure Diamond Cubic Structure is a variant of the zinc blende. Carbons occupy both Zn and S positions. Carbon

16、 (in its diamond form) are bonded by four covalent bonds and produce a tetrahedron.Coordination The coordination number for each silicon atom is only four, because of the nature of the covalent bonding. Other matters A (silicon, germanium etc)物理性能天然金剛石金剛石薄膜硬 度，kgf/mm2100009000-10000體積模量，Gpa440-590楊氏

17、模量，Gpa1200接近天然金剛石熱 導(dǎo) 率，W/（cm.K） (300K)201020縱波聲速，m/s18000密 度，g/cm33.62.83.5折 射 率 (590nm)2.412.4透 光 性225nm25m接近天然金剛石電 阻 率，.cm10161012禁帶寬度，eV5.55.5Graphite Structure（石墨結(jié)構(gòu)）StructureThe graphite structure is composed of layers of the hexagonally arranged carbon atoms.Within the layers, each carbon atom

18、is bonded to three coplanar neighbor atoms by strong covalent bonds.The fourth bonding electron participates in a weak van der Waals type of bond between the layers.分子晶體 (Molecular Crystal) : 組元為分子； 范氏力和氫鍵 若僅有范氏力：無方向性、飽和性，趨于密堆, 常還受分子非球性及永久偶極相互作用影響， 有氫鍵時(shí)：有方向性、飽和性，堆積密度低。多晶型(Polymorphism) 一化合物有兩種以上的晶型相

19、互間轉(zhuǎn)變的形式。 液晶(Liquid Crystal)：可出現(xiàn)液晶相的物質(zhì) 溶(熔)點(diǎn) 清亮點(diǎn) 有些物質(zhì)： 晶相 液晶相 液相 長程有序 （中介相） 短程有序 各向異性 各向同性 炭黑 Carbon black炭黑幾個(gè)（3-7個(gè)）芳香組縮合碳環(huán)平面重疊而成的微晶體。顏料和填料，輪胎補(bǔ)強(qiáng)天然氣、油脂等高含碳量有機(jī)化合物進(jìn)行不完全燒潔（碳沒有完全氧化）。碳纖維 Carbone Fiber 結(jié)構(gòu)的基本單元為石墨層片。亂層石墨微晶，微晶（頭-頭）連接形成碳纖維。制備： 原料： PAN纖維 粘膠纖維 瀝青纖維 （主要） 空氣中 預(yù)氧化 200300C環(huán)化 碳化（惰性氣體）脫氫 石墨化 石墨晶體 C60：

20、巴基球，富勒烯，F(xiàn)ullerenes Rohlfing等人1984年發(fā)現(xiàn)， Kroto等人1996年獲諾貝爾化學(xué)獎(jiǎng) 碳同素異構(gòu)體60（或70）個(gè)碳原子組成的空心圓球，如同足球，12個(gè)正五邊形，20個(gè)正六邊形 的32面體 1.455埃 1.391埃 直徑約7.1-10 埃 球體進(jìn)入晶格， a=14.17埃碳納米管： 巴基管 Buck Tube 碳同素異構(gòu)體全部由碳六邊形組成的中空管，單層與多層（同軸套） 圖直徑， 0.6（10個(gè)六邊形圍成）-幾十納米長度， 10-1000納米2.7 Density computation -ceramicIt is possible to compute the

21、 theoretical density of a crystalline ceramic material from unit cell data in a manner similar to metals.General density Equationp45: theoretical density of a crystalline ceramic material. n: number of atoms associated with each unit cell.Ac: the sum of the atomic weights of all cations in the formu

22、la unit.AA: the sum of the atomic weights of all anions in the formula unit.V: volume of the unit cell.NA: Avogadros number (6.021023 atoms/mol)Example problemOn the basis of crystal structure ,compute the theoretical density for sodium chloride. How does this compare with its measured density?rNa+= 0.102nm rCl-=0.181nmSolution Both sodium and chloride ions form FCC lattices. The number of NaCl u