Chapter 7Introduction to Crystallography7.1 Periodicity and lattices of crystal structure7.2 Symmetry in crystal structures7.3 X-ray diffraction of crystals7.4 Quasi-crystal, liguid crystal and amorphous
Chapter 7 Introduction to Crystallography 7.1 Periodicity and lattices of crystal structure 7.2 Symmetry in crystal structures 7.3 X-ray diffraction of crystals 7.4 Quasi-crystal, liquid crystal and amorphous
CrystallineSubstances:e.g.,Diamond and TableSaltDiamonds
Diamonds Crystalline Substances: e.g., Diamond and Table Salt
7.1periodicity and lattices of crystal structure7.1.1 The characteristics of crystal structure1.Afewdefinitions:Solids canbe divided into twoprimary categoriescrystalline solids and amorphous solidsCrystallineSolidsarebuiltfromatomsormoleculesarranged in a periodic manner in space, e.g., rock salt anddiamond.Amorphous Solids possess short-range order only.Theyare not related through symmetry, e.g. glass, rosin, amberglass.>Short-Range Order:Fixedbond lengths and angles> Long-Range Order:Associated with a lattice point
7.1 periodicity and lattices of crystal structure 7.1.1 The characteristics of crystal structure 1. A few definitions: • Solids can be divided into two primary categories, crystalline solids and amorphous solids. • Crystalline Solids are built from atoms or molecules arranged in a periodic manner in space, e.g., rock salt and diamond. • Amorphous Solids possess short-range order only. They are not related through symmetry, e.g. glass, rosin, amber glass. Short-Range Order: Fixed bond lengths and angles Long-Range Order: Associated with a lattice point
Crystalsare solids that are built from atoms ormolecules arrangedin a periodic mannerin spaceCrystallinevs.AmorphousofSiO2Quartz:(Crystalline)C.N.:Glass:(Amorphous)BothShortandLongRangeOrderShortRangeOrderOnlySi= 4Oxygen0=2SiliconOShort range order: fixed bond lengths and anglesduetothe bonding nature of constituent atoms
Crystals are solids that are built from atoms or molecules arranged in a periodic manner in space. Short range order: fixed bond lengths and angles due to the bonding nature of constituent atoms. C.N.: Si = 4 O = 2
2.Fundamental characteristicsof crystal Spontaneous formation of polyhedral shapesaF+V=E+2DodecahedronIcosahedronCube20facesand 12verticesNo5-foldaxisisallowedinasingle crystal!TetrahedronOctahedronb)Uniformity: periodic distribution of atoms/molecules
2. Fundamental characteristics of crystal a) Spontaneous formation of polyhedral shapes F + V = E + 2 b) Uniformity: periodic distribution of atoms/molecules No 5-fold axis is allowed in a single crystal!