3 - ECE331_Wi06 Crystal Structure If atoms bonded together...

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1 Lu ECE331_Wi06 Crystal Structure If atoms bonded together in a regular 3-D pattern they form a CRYSTAL.- Long range order Each type of atom has a preferred arrangement depending on temperature and pressure (most stable configuration). These patterns known as SPACE LATTICES. Each repeating unit or building block is known as the UNIT CELL. Define UNIT CELL then can define location of all atoms in crystals. There are 7 types of CRYSTAL SYSTEMs (Tab 3.2, C. p40) and 14 standard UNIT CELLs. Lu ECE331_Wi06 Unit Cells
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2 Lu ECE331_Wi06 Metallic Crystal Structures MOST metals crystallize into one of three densely packed structures. BODY CENTERED CUBIC – BCC FACE CENTERED CUBIC – FCC HEXAGONAL CLOSE PACKED - HCP Lu ECE331_Wi06 Atomic Packing Factor (APF) A parameter to describe how dense the atoms are packed in a unit cell. APF = volume of atoms in a unit cell/ total unit cell volume
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3 Lu ECE331_Wi06 Crystal Density number s Avagadro' - N cell unit of Volume - V (g/mol) Weight Atomic - A cell
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3 - ECE331_Wi06 Crystal Structure If atoms bonded together...

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