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Crystalline & Amorphous Solids

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Published in: Physics
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Notes On Solid State phy-Crystalline & Amorphous Solids.

Akhilesh K / Lucknow

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Qualification: M.Sc (NIT Rourkela - 2019)

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  1. A solid consists of atoms, ions, molecules acked closely together, and the forces that old them in place give the distinctive properties of the solid. dhg Q Ionic, Covalent , metallic, van der Waals How they differ from each other ? The way in which the outer electrons of the structural elements are distributed. notes by akhil sir Soli4 st?te physics is devoted largely to the
  2. Crystals & CRYSTALLOGRAPHY AjYhÉfc;s crystal? A crystal consists of building blocks or structural units arranged in patterns that repeats itself in three dimensions. The building blocks may be a single atom or group of atoms or molecules or clusters. e. Crystallography is concerned with/ the description and classification of all possible ty#es of crystal structures and the determination of the actual structure, of the crystalline solids. notes by akhil sir
  3. SöJji1s on of their structure Eyre classified into two groups. Ill) cry31Éj111rve or i) Crystalline Amorphous dhE verilo±ljc is, a representative unit is repeated at Tegular any all directions in the crystal. Most of the solids are crystals. In non-crystals, whether it is solid, liquid groups are arrayed gases the atom
  4. CrySEilljne Solids SPECIFIC FEATURE OF CRYSTAL •UtlISc o c range order Leu Whe position of structural unit remains invariant for a long range. has sharp melting point. 4 It is anisotropic (properties changes _Mith respect to the direction ) e.g ( diamond, rock salt, quartz ) •Sharp peak can be seen under XRD. notes by akhil sir
  5. Mono-crystalline / single crystal]ljne Mono-crystalline crystalline single crystals the periodically extends through out the material ( example quartz) i)Perfect crystal & ii) Impurity 000000 0 crystal Poly-crystalline or crystallites ( many) •In poly-crystalline crystals the periodicity does exit throughout the crystal but it is interrupted at Grain Boundaries. notes by akhil sir
  6. Amorphous Solids They may be regarded as supercooled liquids whose stiffness may be due to exceptionally high viscosity Example: etc. SPECIFIC FEA TURES OF AMORPHOUS MA 4 It is a)short range order. •it is isotropic. •It has a broad melting point . Diffused peaks can be seen under XRD. notes by akhil sir
  7. • Boron trioxide(B203) which occur both in Crystalline & Amorphous forms • In both the cases every boron atom is surrounded by three oxygen atoms. This represent the short range order. But in crystalline form in addition to short range there exist also long range order. • Amorphous form is analogous to liquid which is sypported by X ray.
  8. Amorp oussoi s oe I Its ortmgeor erin elrstruc ures, owever, tinction between the two kinds of order is nicely exhibited in boron trioide (B203), which can occur in both crystalline and amollhous foms. In each case boron atom is surrounded by three oxygen atoms* which represents a short-range order, In a B203 crystal a long,range order is also present, as shown in a two.dimensional representation in Fig, 10, l. Amorphous b203, a vitreous or "glass/' substance, lacks this additional reg, Illality Crystallization from the vitreous state is so sluggish that it ordinarily does not oc- cur, but it is not unlmown, Glass may devitrify when heated until it has not quite be, gun to soften, and extremely old glass specimens are sometimes found to have crystallized. notes by akhil sir
  9. Boron atom Oxygen atom notes by akhil sir
  10. The analogy betirveen an amotphous solid and a liquid helps in understanding both states of matter. The density of a given liquid is usually close to that of the corre sponding solid* for instancq which suggests that the degree of packing is similar. This inference is supported by the compressibilities of these states, Furthemoret x-ray dif, fraction indicates that many liquids have definite short-range structures at any instant, quite similar to those of amorphous solids except that the groupings of liquid mole- cules are continually shifting, A conspicuous example of short.range order in a liquid occurs in water just above the melting point, where the result is a lower density than at higher temperatures because H20 molecules are less tightly packed when linked in crystals than when free to move. notes by akhil sir 10
  11. T e onds in an amorphous solid vary in strength because of the lack of long-range order, When an amorphous solid is heated* the weakest bonds break at lower tem- peratures than the others, and the solid softens gradually In a crystalline solid the bonds break simultaneously, and melting ha; a sudden onset. Metallic "glasses" have been made frÖm mixtures of metals whose atåms differ greatly in size, which prevents them from forming the ordered stmtures of crystals when cooled from a molten state, One such metallic glass has half the density of steel but twice its strength* and is had but cm be deformed without breaking. Its gradual softening when heated make the material exceptionally easy to shape, notes by akhil sir
  12. notes by akhil sir 12
  13. • Bond in amorphous solid vary in strength because lack of long range order. When amorphous solid is heated, the weakest bonds break lower at temperature than the others, and the solid softens gradually. • In crystalline solid the bonds break simultaneously, and melting has sudden onset. notes by akhil sir
  14. Plyzure Uf Whose differ largely in size. This prevent atoms a order from molten state. \half the density of steel but twice It has strength. It is hard but deformed without -freaking. Its gradual softening when heated make the material exceptionally easy to shape. notes by akhil sir 14
  15. • The way of filling up points in a space lattice by the atoms is known as Basis. The specific lattice when combines with the basis generates a unit cell. Specific lattice + basis = crystal structure Unit cell is defined as the basic structural part in the composition of materials. It is analogous to brick used in the construction of buildings. It fills all the space under crystal translation. It may be i) monatomic ii) Diatomic, iii) multi atomic. notes by akhil sir 15
  16. repeat jn a space, a crystal js obtained. -rhe Of the crystal js as Of a repeating -rhe \ SDI L]rrje NJ/ Of a prjrnjtjye cell js LFV3C •crb\/ CC)r) a .gjyer) At ar)cl norrnal 'to three lines clrayy notes by akhil sir this way is the new primitive 16
  17. Primitive and Non-primitive unit Cell -c smållest unit cull jn be for IE Ube MUIume unit célL Tt one atom or one JlÉjÜjoe 1 point pe cell simple cube( sc) If—the unit cell contains more than, one lattice point, then it is called non- primitive unit cell. Example: bcc(2), fcc(4) notes by akhil sir
  18. CRYSTAL SYSTEM ( 7 crystal systerns & 14 Bravajs Ihasve ufjjt célls various geometries. The geometries in terms of ilhejf ao Ibo C antJLllar dimpnsions u, ß and Y. Dimensions a, b and c are along x, y, and z axis respectively and angles u, ß and y are between xy, yz, and zx axes respectively. Bravias has neiäSSified 14 spacé
  19. All crystals fall into one of the seven crystal systems, according to the way in which their symmetry elements restrict the shape of the unit cell. Symmetry is primary, the relationships between unit cell edge lengths and angles are secondary and arise from the symmetry. Cubic, trigonal, tetragonal, hexagonal, orthorhombic, monoclinic and triclinic. notes by ElkhJjl 3jr 19
  20. i i i c 1 at - ara3gc angks al _3 tocs 900 angles a axes = 600 an 90 ISOMETRIC (CUBIC) c b agbßc an 900 ORTHORHOMBIC HEXAGONAL c b a 4b/c angle between a&b and = 900; angk c&a > 900 MONOCLINIC notes by akhil sir c 1 al -a2'c all an#s 900 TETRAGONAL c b agb.c all ar*s 900 TRICLINIC 20
  21. ? ß ? ? ? 90 ? by ElkhJjl 3jr trigonal

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