StructureOfSolids-Me - STRUCTURE OF SOLIDS STRUCTURE Types of solids based on structure Types of solids based on bonding UNIVERSE HYPERBOLIC

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STRUCTURE OF SOLIDS STRUCTURE OF SOLIDS Types of solids based on structure Types of solids based on bonding
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UNIVERSE PARTICLES ENERGY SPACE FIELDS STRONG WEAK ELECTROMAGNETIC GRAVITY METAL SEMI-METAL SEMI-CONDUCTOR INSULATOR nD + t HYPERBOLIC EUCLIDEAN SPHERICAL GAS BAND STRUCTURE AMORPHOUS ATOMIC NON-ATOMIC STATE / VISCOSITY SOLID LIQUID LIQUID CRYSTALS QUASICRYSTALS CRYSTALS RATIONAL APPROXIMANTS STRUCTURE NANO-QUASICRYSTALS NANOCRYSTALS SIZE
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AMORPHOUS CLASSIFICATION OF SOLIDS BASED ON ATOMIC ARRANGEMENT QUASICRYSTALS CRYSTALS Ordered + Periodic Ordered + Periodic Ordered + Periodic There exists at least one crystalline state of lower energy (G) than the amorphous state (glass) The crystal exhibits a sharp melting point “Crystal has a higher density”!!
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AMORPHOUS CLASSIFICATION OF SOLIDS BASED ON ATOMIC ARRANGEMENT QUASICRYSTALS CRYSTALS ADDITIONAL POSSIBLE STRUCTURES Modulated structures Incommensurately Modulated structures Liquid crystals
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THE ENTITY IN QUESTION GEOMETRICAL PHYSICAL E.g. atoms, clusters etc. E.g. spin, magnetic moment ORDER ORIENTATIONAL POSITIONAL PROBABILISTIC OCCUPATION
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ORIENTATIONAL POSITIONAL PROBABILISTIC OCCUPATION Perfect Average Perfect Average Positionally ordered Probabilistically ordered A B Probability of occupation: A 50% B 50%
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When primary bonds are 1D or 2D and secondary bonds aid in the formation of the crystal The crystal structure is very complex Factors affecting the formation of the amorphous state When the free energy difference between the crystal and the glass is small Tendency to crystallize would be small Cooling rate → fast cooling promotes amorphization “fast” depends on the material in consideration Certain alloys have to be cooled at 10 6 K/s for amorphization Silicates amorphizes during air cooling
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COVALENT CLASSIFICATION OF SOLIDS BASED ON BONDING IONIC METALLIC Molecular CRYSTALS Non-molecular COVALENT IONIC METALLIC Molecule held together by primary covalent bonds Intermolecular bonding is Van der walls
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METALLIC Positive ions in a free electron cloud Metallic bonds are non-directional Each atoms tends to surround itself with as many neighbours as possible! Usually high temperature (wrt to MP) → BCC (Open structure) The partial covalent character of transition metals is a possible reason for many of them having the BCC structure at low temperatures FCC → Al, Fe (910 - 1410ºC), Cu, Ag, Au, Ni, Pd, Pt BCC → Li, Na, K , Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Fe (below 910ºC), HCP → Be, Mg, Ti, Zr, Hf, Zn, Cd Others → La, Sm Po, α-Mn, Pu
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CLOSE PACKING A B C + + FCC = Note: Atoms are coloured differently but are the same FCC
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A B + HCP = A + Note: Atoms are coloured differently but are the same HCP Shown displaced for clarity Unit cell of HCP (Rhombic prism)
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Note: diagrams not to scale Atoms: (0,0,0), ( , )
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a CV 4 6 = a CV 12 6 = a VC CF h 3 2 = + = 632 . 1 3 2 2 2 = = = a h a c IDEAL c/a h
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This note was uploaded on 09/27/2010 for the course ME 9421 taught by Professor Pknag during the Spring '10 term at Indian Institute Of Management, Ahmedabad.

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StructureOfSolids-Me - STRUCTURE OF SOLIDS STRUCTURE Types of solids based on structure Types of solids based on bonding UNIVERSE HYPERBOLIC

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