Презентация Crystal defects онлайн
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- Тип файла:ppt / pptx (powerpoint)
- Всего слайдов:43 слайда
- Для класса:1,2,3,4,5,6,7,8,9,10,11
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Слайды и текст к этой презентации:
№3 слайд
![Classification of defects in](/documents_6/7b914d27709b53d912369c879620db7b/img2.jpg)
Содержание слайда: Classification of defects in solids
Zero-dimensional (point) defects
Vacancies, Interstitial atoms (ions), Foreign atoms (ions)
One-dimensional (linear) defects
Edge dislocation, screw dislocation
Two-dimensional (flat) defects
Antiphase boundary, shear plane, low angle twist
boundary, low angle tilt boundary, grain boundary, surface
Three-dimensional (spatial) defects
Pores, foreign inclusions
№4 слайд
![Thermodynamics of defect](/documents_6/7b914d27709b53d912369c879620db7b/img3.jpg)
Содержание слайда: Thermodynamics of defect formation
Perfect → imperfect
n vacancies created
G=Gdef-Gper=H-TS
H=n Hi
Hi: enthalpy of formation of one vacant site
S=Sosc+Sc
Sosc: change of oscillation entropy of atoms surrounding the vacancy
Sc: change in cofigurational entropy of system on vacancies formation
№13 слайд
![AgCl Ag in interstitial](/documents_6/7b914d27709b53d912369c879620db7b/img12.jpg)
Содержание слайда: AgCl
Ag+ in interstitial sites.
(Ag+)i tetrahedrally surrounded by 4 Cl- and 4 Ag+.
Some covalent interaction between (Ag+)i and Cl- (further stabilization of Frenkel defects).
Na+ harder, no covalent interaction with Cl-. Frenkel defects don’t occur in NaCl.
CaF2, ZrO2 (Fluorite structure): anion in interstitial sites.
Na2O (anti fluorite): cation in interstitial sites.
№26 слайд
![Electromagnetic Radiation and](/documents_6/7b914d27709b53d912369c879620db7b/img25.jpg)
Содержание слайда: Electromagnetic Radiation and the Visible Spectrum
UV 100-400 nm 12.4 - 3.10 eV
Violet 400-425 nm 3.10 - 2.92 eV
Blue 425-492 nm 2.92 - 2.52 eV
Green 492-575 nm 2.52 - 2.15 eV
Yellow 575-585 nm 2.15 - 2.12 eV
Orange 585-647 nm 2.12 - 1.92 eV
Red 647-700 nm 1.92 - 1.77 eV
Near IR 10,000-700 nm 1.77 - 0.12 eV
If absorbance occurs in one region of the color wheel the material appears with the opposite (complimentary color). For example:
a material absorbs violet light Color = Yellow
a material absorbs green light Color = Red
a material absorbs violet, blue & green Color = Orange-Red
a material absorbs red, orange & yellow Color = Blue
E = hc/ = {(4.1357 x 10-15 eV-s)(2.998 x 108 m/s)}/
E (eV) = 1240/(nm)
№27 слайд
![Color in Extended Inorganic](/documents_6/7b914d27709b53d912369c879620db7b/img26.jpg)
Содержание слайда: Color in Extended Inorganic Solids: absorption
Intra-tomic (Localized) excitations
Cr3+ Gemstones (i.e. Cr3+ in Ruby and Emerald)
Blue and Green Cu2+ compounds (i.e. malachite, turquoise)
Blue Co2+ compounds (i.e. Al2CoO4, azurite)
Charge-transfer excitations (metal-metal, anion-metal)
Fe2+ Ti4+ in sapphire
Fe2+ Fe3+ in Prussian Blue
O2- Cr6+ in BaCrO4
Valence to Conduction Band Transitions in Semiconductors
WO3 (Yellow)
CdS (Yellow) & CdSe
HgS (Cinnabar - Red)/ HgS (metacinnabar - Black)
Intraband excitations in Metals
Strong absorption within a partially filled band leads to metallic lustre or black coloration
Most of the absorbed radiation is re-emitted from surface in the form of
visible light high reflectivity (0.90-0.95)
№29 слайд
![Cr Gemstones Excitation of an](/documents_6/7b914d27709b53d912369c879620db7b/img28.jpg)
Содержание слайда: Cr3+ Gemstones
Excitation of an electron from one d-orbital to another d-orbital on the same atom often gives rise to absorption in the visible region of the spectrum. The Cr3+ ion in octahedral coordination is a very interesting example of this. Slight changes in it’s environment lead to changes in the splitting of the t2g and eg orbitals, which changes the color the material. Hence, Cr3+ impurities are important in a number of gemstones.
№32 слайд
![Tunabe-Sugano Diagram Cr The](/documents_6/7b914d27709b53d912369c879620db7b/img31.jpg)
Содержание слайда: Tunabe-Sugano Diagram Cr3+
The Tunabe-Sugano diagram below shows the allowed electronic excitations for Cr3+ in an octahedral crystal field (4A2 4T1 & 4A2 4T2). The dotted vertical line shows the strength of the crystal field splitting for Cr3+ in Al2O3. The 4A2 4T1 energy difference corresponds to the splitting between t2g and eg
№40 слайд
![Charge Transfer in Sapphire](/documents_6/7b914d27709b53d912369c879620db7b/img39.jpg)
Содержание слайда: Charge Transfer in Sapphire
The deep blue color the gemstone sapphire is also based on impurity doping into Al2O3. The color in sapphire arises from the following charge transfer excitation:
Fe2+ + Ti4+ Fe3+ + Ti3+ (max ~ 2.2 eV, 570 nm)
The transition is facilitated by the geometry of the Al2O3 structure where the two ions share an octahedral face, which allows for favorable overlap of the dz2 orbitals.
Unlike the d-d transition in Ruby, the charge-transfer excitation in sapphire is fully allowed. Therefore, the color in sapphire requires only ~ 0.01% impurities, while ~ 1% impurity level is needed in ruby.
№42 слайд
![Cu Transitions The d](/documents_6/7b914d27709b53d912369c879620db7b/img41.jpg)
Содержание слайда: Cu2+ Transitions
The d9 configuration of Cu2+, leads to a Jahn-Teller distortion of the regular octahedral geometry, and sets up a fairly low energy excitation from dx2-y2 level to a dz2 level. If this absorption falls in the red or orange regions of the spectrum, a green or blue color can result. Some notable examples include:
Malachite (green)
Cu2CO3(OH)2
Turquoise (blue-green)
CuAl6(PO4)(OH)8*4H2O
Azurite (blue)
Cu3(CO3)2(OH)2
№43 слайд
![Anion to Metal Charge](/documents_6/7b914d27709b53d912369c879620db7b/img42.jpg)
Содержание слайда: Anion to Metal Charge Transfer
Normally charge transfer transitions from an anion (i.e. O2-) to a cation fall in the UV region of the spectrum and do not give rise to color. However, d0 cations in high oxidation states are quite electronegative, lowering the energy of the transition metal based LUMO. This moves the transition into the visible region of the spectrum. The strong covalency of the metal-oxygen bond also strongly favors tetrahedral coordination, giving rise to a structure containing isolated MO4n- tetrahedra. Some examples of this are as follows:
Ca3(VO4)2 (tetrahedral V5+) Color = White
PbCrO4 (tetrahedral Cr6+) Color = Yellow
CaCrO4 & K2CrO4 (tetrahedral Cr6+) Color = Yellow
PbMoO4 (tetrahedral Mo6+) Color = Yellow
KMnO4 (tetrahedral Mn7+) Color = Maroon
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